Earth a 4.5 billion year old Planet still evolving as continents shift and Clash volcanoes erupt glaciers grow and reced the Earth's crust is carved in numerous and fascinating ways leaving a trail of geological Mysteries behind in this episode investigators are exploring the driest place on Earth the atakama desert in Chile this Barren landscape is 50 times drier than Death Valley now scientists are piecing together the puzzle of how this desert was [Music] made from raging volcanoes to colossal mountains oceans the clues they uncover all also provide a window into the formation of the Earth itself Earth is a blue planet engulfed by water but in this desolate chunk of Northern Chile you won't find a single drop wedged between the Pacific Ocean and Coastal volcanoes to the west and the Andes to the east is atak karma the driest desert in the world 600 miles long and narrow on average just 100 m wide it's the same size as Iowa now scientists are on a mission to find out how it was made the investigation begins in the Sleepy town of [Music] kiaga a rare green Oasis its only Lifeline is a stream trickling 300 miles from the Andes to the Pacific it is home to the official government rain gauge so geologist John Houston has come here to find out how dry the driest place on Earth really is this is a plomer it measures the rainfall and every day ah okay for Marissa Vera a government scientist it's a job with few surprises how much rainall has this instrument recorded in the last 15 years less than 1 mm a year less than 1 mm a year yes was it every year it rains only 3 years that's incredible exactly so less m a year on average it rains 3 100s of an inch a year it would take a century for atak Karma's rainfall to fill a coffee cup how does this compare with other deserts here we have a cylinder and I'm going to show you the difference between the amount of rainfall perom here and the amount of rainfall in other deserts so if I fill this jar up right up to about there that is roughly grainful that you get in the Sahara now if I pour most of that away we get to that level that represents what we have in the Mojave Desert 5 in in per them if I pour all that away except for that little drop in the bottom there and that's the equivalent of what we have here in the heart of the atakama desert that is such a small amount of rainfall that it means it's the driest place on Earth in his quest to find out why atakama gets so little rainfall Houston leaves the Oasis behind and heads into the desert by the side of the Pan-American Highway a road which runs the length of the continent he discovers the first clue well here we are at the traffic of Capricorn this is one of the most important latitudes in the world and it is absolutely critical in explaining why the atakama desert is in this location here most of the world's deserts straddle one of two special [Music] latitudes in the southern hemisphere the Tropic of Capricorn runs through atakama and Africa's Namib and Kalahari deserts in the north the Tropic of Cancer runs right through the vast Sahara at these particular positions on the planet the air is extremely dry this instrument is called a whirling hygrometer what this does is to measure the relative humidity of the air and the reading on here gives us a relative humidity of 10% that's really low really low um there aren't many places in the world where you get a relative humidity as low as [Music] that back in the early 1700s scientists discovered why tropical air is so dry European ships sailing to America relied upon the trade winds to power their Crossings but English meteorologist George Hadley was mystified why they blew Westward when they should blow directly north his studies would lead scientists to understand how air circulates around the [Music] Earth at the equator moisturer air gets heated by the Sun and Rises as this hot wet air flows away from the equator it quickly sheds its water as Rain by the time it reaches the two Tropic latitudes the air has lost nearly all of its moisture resulting in no rain on the land below the mystery though is why atakama gets so much less rain than any place else scientists hope to Crack the Case by figuring out how atak Karma first formed on the hunt for Clues Houston travels deep into the true desert this closely guarded location was discovered during routine mapping by geologists back in the 70s but the huge significance of their find wasn't realized until 1998 this band of Boulders is the single most important clue to atacama's Beginnings it's a delicate rock called gypsum a simple Test shows how fragile it is if I pour a little bit of water on top of that you will see that it very rapidly falls apart What's Happening Here of course is that when I'm putting water on this you see it dissolve I mean it's just going to fall apart the survival of as a solid rock tells scientists there hasn't been any Heavy Rain since the rock formed so the next step was to date it and figure out when this place became dry gypsum can't be directly dated but by analyzing fossils in the surrounding rocks the awesome age of the desert was revealed atakama is a staggering 50 million years old this gypsum here is an extremely special gypsum if there had been any rainfall greater than 2 in in any one year this would have dissolved and have been washed away what that means is essentially that the atakama desert is the oldest desert in the world for more than 15 million years while dinosaurs thrived and became extinct the Himalayas formed and humans evolved atakama has been a desert gypsum also holds the key to how this desert was made it's a chalky mineral which forms not in deserts but in water gypsum exists in a dissolved state in Shallow warm tropical Seas as the water is evaporated Away by heat it solidifies the existence of this one little rock is a key piece of evidence which reveals that before atakama became a desert it was a [Music] seabed this really ins significant looking piece of rock indicates that all this desert was once underwater so this gypsum in this location in the atakama desert is absolutely critical to understanding the whole history of the atakama desert in the investigation so far scientists have pieced together evidence of how and when the desert first formed at a Karma's location near the Tropic of Capricorn means air is dry and no rain falls fossils found in the surrounding gypsum Rock reveal the age of the desert gypsum a rock that forms only in water reveals atakama was once underwater now as scientists explore the mystery of how atakama evolved from ocean floor to Pure desert they unearth explosive evidence in the investigation of how the driest place on Earth was made 150 million years ago the atakama desert was a seabed covered by ocean waters but today some areas in the desert are 2 miles above sea [Music] level in the journey to find out how this happened scientists take the investigation to the Eastern edge of the [Music] desert this strange landscape is the largest geyser field in the southern hemisphere we're up at the Alo geyser field you can see around us that there's plenty of hot springs and Geyers there's plenty of steam around and this is cuz the air is cool and the water is hot and so you have a lot of steam and and bubbling Springs the boiling water is being heated deep underground the geers and the hot water that you find up at El tatio are indications that you have a body of hot rock underneath us and another indication is you have a bunch of volcanoes surrounding this Basin the Earth here is violently alive molten rock erupts onto the surface forming volcanoes the fiery volcanoes and the boiling geysers are evidence of a turbulent process happening deep beneath the desert here the Pacific ocean crust is being forced underneath South America much like a spatula going underneath a pizza this geological process is called subduction you have the Pacific Plate colliding with the continental crust and the Pacific Plate is actually heavier and it slides underneath the continental crust and as it does so it Heats because it gets to a depth of about about 60 miles and it becomes molten this crucial depth is called a melting Zone hot molten rock then thrusts upward to form the active volcanoes that ring the eltio geyser field this process gives scientists a hint to what lifted the desert out of the ocean more clues are found on the opposite side of the desert geologists know that these Coastal Hills were also once volcanoes today they're completely dead but modern dating techniques show that they first erupted over 195 million years ago it's a crucial piece of evidence which reveals when the Pacific Plate first began to force its way beneath South America at that time the desert indeed all of Chile was under water over time the melting Zone was pushed further and further Inland first igniting the coastal volcanoes as the melting Zone passed beneath the desert it Formed new crust thickening and raising the land the atakama desert slowly [Music] emerged 50 million years ago this same process began to raise the Andes today the melting zone is 140 Mi Inland and the molten rock it produces ignites volcanoes and fuels ELO's geysers but as it passed under the atakama desert it also left behind this chuki kamata the largest open pit copper mine in the world volcanic processes concentrated the copper ore here but it was the desert's unique climate that locked it in place this area of Northern Chile produces some of the largest and most important copper deposits in the world and this is largely due to the very dry climate most of the erosion on the earth's surface is caused by water so here where there's so little rainfall and there's very little surface water there's not very much erosion and so the copper deposit has actually remained intact as a result this Barren Wilderness is one of the most valuable pieces of land on the [Music] planet the mystery of how a desert can rise from the SE can be solved geysers provide evidence that molten rock exists deep underground the existence of active volcanoes shows the movement of one continental plate under another extinct volcanoes show this process began at the coast and pushed Inland raising the desert above the ocean the next step is to try and figure out what turned the this ancient sea Flor into the driest place on earth a quest that spans 200 years of history and solves the riddle of what brought these penguins to the edge of the [Music] desert the atakama desert is intriguing because it is the driest place on Earth deserts by their very nature are dry but atakama is unique it's 50 times drier than Death Valley in California and it's not because it's hotter atakama averages around 80° fah during the day whereas temperatures in Death Valley regularly soar above 110 the search for what turned this strip of land from a regular desert into to the world's driest place begins out on the Open Sea one of the curious things about the atakama is that we actually see here penguins penguins obviously like cold water and that's really confusing when you think of on Shore we have really hot conditions in fact the temperature of the water here is about 55° F whereas on land the temperature is something like 80° [Music] F these penguins were first described by explorer Alexander Von humbold over 200 years ago while traveling along this Coast he was puzzled by the huge variety of marine life measuring the temperature of the water gave him an explanation it was 20° colder than expected perfect for sea life like penguins centuries later meteorologists began to wonder if this chilly belt of water called the humbled current after the Explorer was the reason atakama became the driest place on Earth the hanbul current comes all the way up from Antarctica bringing with it cold water and it is this cold water which creates this dull gray day that we see here with a fog overlying us it causes the air above it to cool forming a thick Bank of cold cloud and fog which clings to the shore hot dry air descends at the Tropic here that hot air sits on top of the cold heavy rain clouds holding them down meteorologists call this an inversion layer trapped at 3,000 ft the clouds can't rise up and shed their rain on the High Altitude desert the inversion layer prevents any moisture that may accumulate close to the sea from moving Inland so that is one of the reasons why this hum current actually contributes to the dryness of the atakama desert that we see just over [Applause] [Music] there but is it this inversion layer created by the humbled current that has turned atakama into the driest desert in the world in the desert's Northern tip in a desolate place called kada Aroma geologist Laura evenstar is looking for Clues to solve this riddle she's trying to put a date on when the desert became so very dry other deserts like the Mojave don't get much rain but when they do it's dramatic storms bring heavy rains and flash floods but not here in the cabada aroma which is now totally dry one way to date the last time there would have been enough rainfall to cause a flash flood is to try to find out how long the rocks have been lying there undisturbed what we have here is a a miniature demonstration of what goes on if we start having large amounts of rainfall so this is our rainfall here and what we can see is that when we start raining on our desert surface it will pick up the boulders and move them around and then when there's no water here the boulders just sit still and don't move the surface of cabada Aroma is strewn with rocks so she's cracking them open to reveal evidence of exactly when water last flooded the landscape what we do is we have to knock a bit off and then we examine it and have a look at whether it's got a very dark color and hopefully we can be able to see some of the black minerals which is what we're looking for the tiny black crystalline minerals are [Music] pyin they're crucial evidence because like microscopic geologic clocks their chemistry changes when exposed to Cosmic radiation over time the sun is only producing a tiny bit of the radiation which will hit this rock the majority of it is coming from all the stars you see in the night sky what it does to the rock is basically uh just bakes it a bit like a really bad suntan so it just comes down hits it and Cooks it as The Rock gets cooked by cosmic rays the pyroxenes break down and produce a gas called helium 3 we can record how much helium 3 is within this rock and the more we have the longer that it has been exposed to Cosmic or uh solar radiation helium 3 gas is only produced in microscopic quantities so evenstar takes her samples to a lab 7,000 M away in Glasgow [Music] Scotland so what we do uh using a laser is we shoot the laser into one of the wells and vaporize our [Music] crystals and that's releasing the helium 3 then the helium 3 is going to go through all this complicated machinery eventually run through the mass spectrometer by analyzing this data she can figure out the last time the boulders were moved the oldest age sample we've actually recorded has been 23 million years so what this means is that within certain areas of the atakama desert these Boulders have been sitting there and not moved by water for 23 million years soat desert is one of the oldest undisturbed surfaces in the world these Boulders were there before humans even started to exist they are incredibly old even start has discovered that there are places in the desert which have been bone dry for 23 million [Music] years this date is a crucial clue in the investigation because it coincides with the birth of the humble current South America was once joined to Antarctica but roughly 25 million years ago these continents split a channel opened freezing water began to circulate round the pole and thundered North along the coast this cold current formed an inversion layer trapping Coastal rain clouds and starting atacama's slow transformation into the driest place in the world but the humbled current is not the only culprit ironically the quest to find out how the desert became so dry comes up against one of the wetest places on Earth on the other side of atakama is the Amazon on but the heavy rainfall from the rainforest doesn't get anywhere near the desert the reason why is in plain sight between the Amazon and the atakama desert lies the vast Andes mountain range geologic evidence suggests the Andes finally grew high enough some 10 million years ago to prevent any rain from reaching the desert it's called a rain shadow effect and it's the final factor which drove atakama to become the driest place on [Music] Earth the evidence for what Turned atakama so incredibly dry is mounting the humbled current creates a weather system that allows no rainfall helium 3 in Rock shows that the process of desiccation began 23 million years ago ago the rising Andes 10 million years ago made it drier still the investigation would seem to be conclusive atakama has been a Barren essentially rainless landscape for millions of years but then something happened to blow that conclusion wide open Tiny shards of stone reveal that an ancient civilization once lived here but how could people live in the world's driest desert the atakama desert is by far the driest place on Earth and by piecing together the evidence scientists believed it had been so for millions of years [Music] yet at a remote site called guanacos paleo ecologist clao lore made an intriguing discovery which paints a more complex picture this is a an extraordinary find and this was probably a little knife or a scraper that's been broken off and discarded it's actually probably still cut to the untrained eye it looks like a simple Rock Shard but lore can see it's been worked into a tool and he's found hundreds of them they're clues that reveal ancient humans once lived here this was not just a temporary residence this was something where people were living and working and banging away at rocks and making artifacts and living off this landscape using the resources at hand [Music] as water is essential for life it seems impossible that any kind of plant animal or human life could survive here Lor suspects that some regions of this 57,000 squ mile desert were once much wetter not millions of years ago but during the time humans walked the Earth in 1997 he set off on a mission to hunt for evidence today he's retracing that Journey changes in the climate can be seen in the Rocks so lore examines the cliff layer by layer he finds a crucial piece of [Music] evidence this is actually where the interesting part of the story comes in this chalky rock is called diatomite it's made from the crushed remains of fossilized algae microscopic life forms which only live in fresh water what this rock is telling us is that we had basically a wetland whereas you look at the landscape across the day and we see that it's basically about as dry as you can get sometime in the past there was water on the surface of the desert Lor's next task was to find out when radiocarbon dating is one of the most accurate methods of dating but using this method means sampling something organic so Lori combed the desert for Clues the way we work is basically poking our heads into every little hole in crevice that we can find when we found this place we couldn't believe our eyes he accidentally and luckily stumbled upon the most important piece of evidence in this investigation at the back of the cave was a vast [Music] Nest it's made from the feces of thousands of generations of tiny mammals the size and shape of the pellets told lore those animals were chinchilla rats and it also contained the critical clue he was searching for organic material when we found the site one of the most exciting discoveries that we made was the fact that it's full of grasses now look across the landscape today and tell me where those grasses are and we immediately knew that we were talking about some major vegetation change this grass looks as fresh and crisp as if it was collected yesterday but when Lor carbon dated grass from the nest what he found was amazing the grass was more than 11,000 years old what I have in my hands here is been ecosystem this is about as clear an indicator you can get better than anything else you can think of that water increas in the pass in this area The Nest reveals strong evidence that plants and mammals did exist here and they weren't alone underneath the thick layer of Nest is another layer rich with tiny handmade tools if we look around you know we can find actually evidence of this past occupation U there's just full of little shards here on the floor some regions of atakama have been constantly dry for 23 million years but this evidence shows that other regions like guanacos were very different 11,000 years ago it's a fossilized snap snapshot of a diverse ecosystem briefly bursting into life grasses grow and wetlands flourish in this wetter time tiny mammals Thrive and breed while game like vuna and llamas meant humans could live in this rich and fertile environment so it's wonderful to know that by looking at something as mundane as a a Rodin Nest you can actually find clues that enabl you to understand the past human colonization of the AMA desert which is no mean feet in itself given the fact that it's such a harsh climate today the date of The Rat's Nest gives scientists a possible theory of where the water came from 11,000 years ago the last Ice Age was at an end the global climate was changing more rain fell high in the Andes flowing down to the desert in rivers in some places groundwater pooled forming Wetlands others remained Untouched by water as they had for millions of years but just a thousand years later the climate changed again Rivers dried up grasses died rats and humans disappeared now every drop of groundwater has been sucked down into the parched Earth lore demonstrates how deep that water is today so just to give you an idea of how much change has gone on since the wedland was formerly at the surface here's a little experiment that we can do this is a well and I'll drop this it'll Rock and we're going to count and we're going to see how long it takes for that rock to hit the water so that takes almost 4 seconds to reach the water that's well over 200 ft below the surface is where the water table is today it's about as dry as it gets it's a it's what we call absolute desert no plants no Wildlife nothing no surface running water whatsoever the investigation of this driest place on Earth took a surprising turn tools show humans lived here diamite reveals the climate was once wetter rats dung and grass dates a diverse ecosystem to 11,000 years ago yet this extraordinary desert has more secrets to tell not just about life in one of the most extreme environments on our planet but also about life on other planets today scientists suspect atakama is the driest it has ever been so they in investigating whether there's any source of water left here at all and NASA scientist Alfonso deila knows that if there's water there's a chance there could be life here too but when he first arrived the signs didn't look good when I came here for the first time I drove for a couple of thousand miles and when I got uh back to my base camp I realized that I didn't have have a single insect smashed against my windshield uh that has never happened to me anywhere else in the world and I think that's a very good example of uh how hard this environment is for life since the 1960s NASA scientists have been hunting for bacteria life in the desert's thin soils yet they found nothing until 2005 when they came across a strange white landscape [Music] by chance one of D vila's colleagues picked up a rock smashed it open and discovered something completely unexpected yeah you can see very nicely uh a Green Layer inside the crust under the microscope the significance of this pale green blur zoomed sharply into Focus to our surprise we saw a green microorganisms living inside the rock so that came as a big surprise uh because nobody was expecting microorganisms in the middle of the driest place on Earth completely by accident hidden inside a rock they discovered life this mineral is sodium chloride otherwise known as halite it's a very common mineral in the arama desert and it's also very common mineral in kitchens around the world as this is exactly the same salt we use to spice our foot salt can preserve food by killing off bacteria but here strangely it was harboring a colony of green microbes to find out how they survive Dila laid out a series of sensors that measure measure humidity his research shows that although on average the air in the desert is around 10% humidity on rare occasions it rises as high as 75% this momentary increase in water vapor is the only source of water and it's this water that gives rise to life the distinctive property of salt is its capability to extract water vapor from the atmosphere and forms a liquid solution inside the rock as moisture from the air is sucked into the salt the microbes allow the rock to bring the water to them life is actually very robust it's uh very flexible and it can really adapt to some of the most extreme condition I that we see on [Music] Earth NASA believes this discovery in the atakama desert can reveal something about life on Mars in 1976 the Viking Lander detected water in Mars's thin atmosphere in 2008 NASA's Mars Odyssey Orbiter found evidence of salt on the planet's surface now when humans finally get to Mars they won't be looking for life in the thin Martian soils but inside the Rocks unfortunately it's going to be a long time until we see humans Walking on Mars until then we come to the atakama desert uh and we study these type of rocks which likely hold the clue to understanding life on Earth and also to understanding the potential for life in other planets in our solar system so it's possible that an accidental Discovery in the driest place on Earth will one day lead scientists to crack open a martian Rock and discover little green alien [Music] life the investigation into how the driest place on Earth was made has revealed an awesome Earth story spanning 150 million years gypsum a rock which forms in water shows the desert was once a seabed hot geysers show that immense volcanic activity Under the Desert raised it above the ocean tiny pyxine crystals revealed the first areas of the desert which became completely dry 23 million years ago rat nests reveal a small pocket of life that bloomed in the desert at the end of the last ice age tiny green organisms in salt show that even here life clings on today this place is unique on Earth absolute perfect desert and the investigation into how it Formed has shed light on another chapter in the story of how the Earth was [Music] made Earth Earth a 4.5 billion year old Planet still evolving as continents shift and Clash volcanoes erupt and Glaciers grow and recede the Earth's crust is carved in numerous and fascinating ways leaving a trail of geological Mysteries behind in this episode an investigation into California's San Andreas fault the greatest fault line on Earth 800 M long this ugly scar on the landscape has spawned earthquake after earthquake but for now it waits quietly deep under our cities building up stress to strike once again the San Andrea's fault is one of the most dangerous geological features on Earth [Music] California's greatest cities and millions of her citizens live in constant Peril since records began there have been 13 large earthquakes along the San Andreas fault the water lines have ruptured their there's no water coming out of the fire hydrant and now America's geologists her Rock detectives are warning of a potential disaster the major damage has been done in the fall of 2008 more than 300 scientists calculated what a major earthquake would do to Southern California we've been conducting a special study of a magnitude 7.8 earthquake on the southern Sant Andreas fault large enough to potentially damage tall buildings fire will be very significant the definitive scientific report presented to politicians was codenamed ShakeOut it forecasts thousands of deaths and billions of dollars of damage in the city of Los Angeles which makes it crucial to investigate the most important question when will the next big earthquake hit the San Andreas Fault us the latest preparations for disaster are the climax of an investigation that started more than 100 years ago in the aftermath of the great San Francisco Earthquake of 1906 the earthquake struck on a Wednesday Just Before Dawn the ground shook violently for 40 5 Seconds igniting fires that raged unchecked for the next 4 days 28,000 buildings a tenth of the entire city were destroyed and more than 3,000 people one in every hundred of the population were killed with a magnitude of 7.8 it's in the top 20 of North America's strongest ever earthquakes the scale of the great San Francisco earthquake shocked the nation but no one understood what had made the city [Music] Shake Native American myths explained earthquakes as shocks from a battle between Waring Spirits Latter-Day explorers couldn't understand the shocks that destroyed their mission buildings one Spanish missionary wrote the Earth shook around me from explosions under the ground 300 years later and science has still made little progress refugees in the ruins of San Francisco still blamed earthquakes on mysterious underground explosions so just 3 days after the earthquake the state of California asked one of the world's most famous geologist S Andrew Lawson from California State University to investigate what had destroyed the city he and a team of 25 scientists began collecting damage evidence in the City and surrounding Countryside there were roads that had buckled rail tracks that had Twisted the most startling evidence of all that came near the town of bolinus in Maron County to the north of San Francisco this picket fence had an 8T Gap in the middle before the earthquake it was a solid boundary fence dividing two Fields but when he recreated what had happened Lawson realized that the land had jolted apart and torn the fence in two plotting the evidence on a map around San Francisco revealed a surprising pattern because connecting the dots drew a straight line and at every point the Earth moved in the same way on the coast to the north Inland to the South this line of weakness was the culprit they were searching for South of San Francisco the suspect line ran underneath a lake the lagona de San Andreas so now the earthquake perpetrator at last had a name Professor Lawson who a decade earlier had identified cracks in the earth here as a harmless Rift now rechristened it the San Andreas Fault in modern day San Francisco the buildings the roads and the railways have long since been repaired but if you know where to look evidence of the 1906 Quake can still be found geologist Charlie Paul follows in the footsteps of Lawson's team seeking signs of the Havoc from 1906 he finds it on the Cliffs at muscle Rock 12 Mi South of San Francisco The Cliff is not here by accident there's a very good reason why this Cliff is here half a mile or so of the shore face apparently fell off in the 1906 earthquake and if you look down below us there's a big rotated block um that's near near the present day Shoreline and it is just in Board of the San Andreas fault the San Andreas fault is uh about a quarter of a mile offshore here and of course that's one of the major crustal Junctions um on this side of North America modern computers can now Trace how damage waves spread out across the city and that pinpoints where the Quake originated along the San Andreas it was offshore about 2 miles out to sea from the Golden Gate Bridge so to continue tracking the fault the investigation must head out to see Marine geologists use remote operating Vehicles mini submarines to map the seafloor what You' see is subtle variations in the topography or topography that would not naturally line up so there might be a line on the ocean floor that is higher or lower on one side and you can use various techniques to determine that this actually is a fault instead of some other process running South across the seabed the San andreus finally runs out of ocean and hits the land this broken line of rocks stretching in from the sea marks where the San Andreas hits land 12 miles south of San Francisco yeah we're here at muscle Rock and we're essentially standing on the San Andreas fault right now and uh if there was an earthquake I don't know what would happen right here but I wouldn't want to be here this Pacific Coastline where Cliffs crumble slowly into the sea is the boundary between two of the Earth's massive continental plates separated by the San Andreas fault two vast separate blocks of the Earth's crust lie directly alongside each other here the continent of North America lies slightly on top of the adjacent section of crust which holds the Pacific Ocean the join can be seen where these lower darker rocks are overlaid by light colored sedimentary rocks these rocks typ differ by by uh more than 100 million years in Age Two Rock bodies that uh are not similar in any way have been brought together the fault line was exposed to geologists when the cliffs collapsed here in the 1906 earthquake but back then nobody understood how and why the two different types of rock were next to each other until around 40 years ago when the answer was finally revealed by the theory of plate tectonics the theory showed that the Earth's crust consists of separate moving plates on which the oceans and continents [Music] sit around 200 million years ago the heavy Pacific ocean plate collided with North America and started sinking underneath the lighter continent professor geophysics Mark zobac studies that process called subduction in his laboratory at Stanford University for many millions of years prior to the existence of the San Andreas fault the Pacific Plate was subducting beneath North America the oceanic plate was diving down and uh that process went on for well well over a 100 million years so a tremendous amount of activity was occurring as the Unstoppable force of one plate met the immovable object of the other they were forced to change direction about 20 million years ago the play motions were such that the Pacific Plate had to start sliding North with respect to North America and now you know the the principal motion is this sliding process between the two plates and 20 million years ago the San Andreas fault was born it was the moving plates that crushed different types of Rock together just as here at muscle [Music] rock at last the investigation knows what it is dealing with the San Andreas fault is 800 M long emerging from the seabed north of Point Arena in Northern California and running down to the sultan sea in the South the evidence is coming together Clues from the 19 1906 earthquake such as the picket fence that was torn apart prove that the land was moving connecting the dots identifies the straight line of the San Andreas fault and muscle Rock uncovers different plates of the Earth's crust on either side of the fault line but investigators still need more information about how often the San Andreas has spawned earthquakes in the past it might help them answer the all important question when will the San Andreas strike again to discover when the San Andreas fault will strike again the investigation needs to know about ancient earthquakes that have struck along the fault [Music] line but there's an immediate problem here in California it's a particular Challenge and some of the earliest written records were from the missions and from the early explorers so only dating back into the 18th century here other parts of the world we have an earthquake history going back Millennia the investigation moves 350 Mi South of San Francisco to a desert where the San Andreas may have been active for thousands of years there's Cru cral evidence here about earthquakes from ancient times this Creek used to flow straight across the San Andreas fault here but several earthquakes formed a Natural Dam where the San Andreas fault wedges up here in front of me that created a small pond and now we're looking at the dry sediments of that pond that record the history of earthquakes and that tells us quite a great deal about the past behavior of the San Andreas fault some of the clues are so small that HUD nut's detective work gets him down and Dusty among tiny cracks inside the fault sometimes we can find out about the past behavior of the San Andreas Fault by looking at the tiniest details at the bottom of this small ancient Pond mud sediments collected above a fine line of Pebbles then an earthquake shifted the land upwards on one side of the vertical fault line so this layer was originally flat and then in a subsequent earthquake it was broken like this along this tiny fracture strand of the San Andrea's fault but finding proof that this is the sight of an ancient earthquake is only part of the story hudnut needs to know how long ago it happened the bare rock layers are no help in dating his find but just above the fracture line of the Rocks he has found the evidence he needs here a bush was burned by a prehistoric wildfire and that remnant of carbon is why you see this black stain on the side of the trench wall the key to unlocking the age of the Rocks is carbon 14 known as radiocarbon its molecular structure means that carbon 14 is a more unstable isotope than other forms of carbon it's absorbed by growing plants then radioactively decays at a known rate after the plant dies so measuring carbon 14 in vegetation burned in a wildfire reveals how long ago those plants died and dates The Rock in which the carbon is found and through this we can reconstruct the evidence of the past earthquakes radiocarbon dating has proved that earthquakes have been happening along the line of the San Andreas for thousands of years the particular small earthquake investigated by hudnut for example is around 32,000 years old it happened at a time when the last woolly mammoths were dying out in North America the investigation moves to an even more remote desert spot the kizo plane 160 Mi north of Los Angeles here lies a dried up riverbed which takes an unusual course coming down off the hills the creek bed takes a sudden sharp turn to its right a few hundred ft later it makes an equally odd 90° turn to the left the creek crossed the line of the San Andreas fault but early geologists were mystified why did it Bend in this way the scientific Pioneers were limited to studies on the ground nowadays hudnut has an advantage he can take to the [Music] air the San Andreas Vault where it cuts through the cizo plane it almost looks like a scar and it was caused by repeated earthquakes in the past along the long line of Hills marking the course of the San Andreas hudnut spots the puzzling bends that he's seeking oh if we could swoop along the fault through here that would be awesome oh there's a great angle see that right angle uh offset Channel with the elbow in it right there that's a classic one right there HUD nut's aerial view of the creek bed shows that the river once flowed straight on across the fault but little by little a series of earthquakes along the San Andreas dragged the creek away from its original course recreating how the land had moved showed hudnut that the two parts of the creek had traveled more than 300 ft apart so if you imagine the North American Plate is fixed and the Pacific Plate is moving to the Northwest the Wallace Creek site records that offset because the channel was straight across the fault but it's been offset through time earlier investigators had already radio carbon dated the land on each side of the F tier revealing that it took 3,000 years to change the Creek's position so knowing the distance and the time it took to do it lets hudnut calculate the average speed with which the two land masses are moving past each other 300 ft in 3,000 years one foot per decade just over an inch a year but this was never a steady sliding 1 in a year movement the reality was a series of sudden small jumps whenever tension built up enough between the two moving plates to overcome friction between the rocks and rip the land apart with an earthquake it's an important moment for the investigation knowing how fast the land is moving not only reveals the stress that's building up but also the risk of an earthquake the San Andreas fault is giving up its Secrets Clues from a long dried up Pond reveal the sight of ancient earthquakes carbon from a prehistoric fire provides the dates and bends in a riverbed prove how fast the plates are moving along the San Andreas but now the investigation has a new mystery to solve if the land along the San Andreas is moving 1 in every year causing earthquakes then why has one small town along the fault line never had [Music] any the investigation has discovered how fast the land is stretching and straining along each side of the San Andreas fault which should help establish when that ever increasing stress will snap the land apart in the next major earthquake but there's a problem one part of the fault line just doesn't fit the pattern the small town of Hollister is unique along the San Andreas fault system it's never had an earthquake and the investigation is going to find out why Hollister has a population of 37,000 and nothing here is quite the way it should be there are plenty of Clues suggesting that the land must be moving here sidewalks with cracks in curbstones way out of line and walls that are bent out of shape walking through the polister we can see anything that man has built that was laid out in a straight line may have a jog in it every year it changes a little bit and it's a progressive thing the clues add up to one clear conclusion even without any earthquakes the Earth in this town in the heart of the San Andrea system still slides imperceptibly slowly and effortlessly along in in one sense the damage that you see here associated with the creeping is is clearly sort of under control but as a geologist if you start playing that out for tens of thousands or hundreds of thousands or millions of years the consequences of that become enormous for many years the creeping ground that moved without earthquakes remained an unsolved [Music] mystery but then the investigation moved 100 m South to another small community where the land also creeps [Music] along the village of Parkfield has a population of just 37 people and a bridge which spans right across the San Andreas fault the bridge separates the Pacific Plate on one side from the North American Plate on the other and the bridge railings have started to bend I'm right now on the Pacific Plate on the west side of the San Andreas fall and you know the the San Andreas comes off the flank of that hill and right across that field right under the bridge and then right over by the corner of that building or that fence post and then on off to Middle Mountain the movement here around the bridge is strikingly similar to the slow creeping ground of Hollister but there is one important difference here in Parkfield every couple of decades or so this Village does have earthquakes they're just little Tremors but they're big enough to be recorded on earthquake monitoring seismographs that's why the village proudly boasts of being the earthquake capital of the world but it's perhaps more accurately called the earthquake study Capital because scientists are fascinated by the fact that earthquakes here follow a predictable pattern elsewhere earthquakes always strike without warning the toll of death and destruction made worse because nobody knew they were coming so scientists are desperate for any clues that might help predict when an earthquake could happen and here in Parkfield the earthquakes happen with astonishing regularity on average every couple of decades or so minor Quakes happened here in 1857 1881 1901 1922 1934 and 1966 after the 66 earthquake investigators set up a network of monitoring instruments to see if the fault gave any warning before the next earthquake arrived they expected it sometime between 1988 and 1993 but it was late and months of waiting stretched into years but still the scientists waited until finally in December 2004 the long awaited earthquake arrived and was caught on film from a now slightly worn and damaged camera the earthquake movie may not have seemed that impressive but the instruments collected a mass of information the data didn't after all help with earthquake prediction but it did pick pinpoint where the earthquake started underground which told investigators where to look next deep down under the Parkfield Countryside starting slightly to one side of the fault the aim was to angle in and stab into the very heart of the San [Music] Andreas after 3 years of drilling long cores of rock were extracted from the exact spot where where the earthquake occurred this was the first time that team leader geologist Mark zobac had ever seen rocks from the center of the San Andreas what we're looking at here are cores from the active San Andreas fault from a depth of about 2 miles so for the earth science Community uh these are like moon rocks as we were trying to exume these cores we had a great deal of drilling difficulty the San Andreas fault was literally fighting back back after 9 weeks of attempting to recover the cores in the middle of a huge lightning storm almost a scene directly out of Hollywood with the thunder and lightning these cores came to the surface and so it was a tremendous feeling of satisfaction um the lightning and thunder just made it that much more dramatic and we're all wearing gloves we didn't want any oil from our fingers to affect the core and the the rule was that you touch the core as little as possible obviously I'm not going to wait for you guys oh look at this beautiful Rock the reality was we couldn't help ourselves and uh um it was just such a remarkable thing to be actually looking at the San Andreas fault uh for the very first time that that we all got to touch it a little bit buried within the rock cores they found a vital clue about the way that land slips along the San Andreas they found serpentinite serpentinite is an unusual rock type it was originally formed uh at the base of the ocean crust and ex zoomed up onto the continent but the reason that serpentinite is so interesting is that serpentinite is very easily altered to Tel it allows the rock to slide at very low Force levels it's tal and powder is very slippery Tal's crystallin structure of soft sliding flat PL makes it one of the slipperiest Rocks known to science so T could well be um a key mineral in in deciding how the fault is actually working in in central California we see that the secret of the slipping San Andreas vault is actually the Rocks themselves the talc explains the tiny earthquakes of Parkfield nobody's yet drilled to investigate the rocks at Hollister but science scientists suspect the tal is present there too cracks in the walls show the land Creeps in Hollister and a bend in the bridge reveals the same creeping ground in a nearby Town rock cores extracted from the fault contain serpentinite leading investigators to the softest and slipperiest mineral talc which lubricates some parts of the fault the investigation is having success but one crucial question remains to be answered what will the San Andreas fault do next the investigation into the San Andreas fault is trying to predict when and where its next major earthquake will strike so far the only certain prediction is the far distant future of the San Andreas look 20 million years ahead if the plate movements continue to follow their pattern Los Angeles will end up becoming a suburb of San Francisco but predictions on a shorter time scale are more difficult if you were to ask the question can we predict earthquakes my answer would be no because I know what your question really meant is you can we predict that an earthquake is going to occur on a certain fault at a certain time that we can specify in the future and we cannot do that but there are many things we can predict we can predict which vaults are likely to produce the big earthquakes we can predict how big the earthquakes are likely to be and we can even predict the probability of the earthquake occurrence over some period of several decades predictions are most crucial where the San Andreas runs to the south of LA here in the Coachella Valley desert geological evidence of earthquak stretches back 1500 years and more and they follow a regular pattern major earthquakes strike here with monotonous regularity every 200 years but the latest one is long overdue there hasn't been an earthquake here for more than 300 years that's a concern because parts of the San Andreas fault system run straight from here towards the city of Los Angeles The Faults will transmit earthquake shocks in a straight line towards California's biggest city geologist Yuri fialco regularly monitors how the ground moves on either side of the fault line he lines up his GPS equipment precisely over a series of metal pegs fixed into to the ground this information is crucial for estimating how fast the fult slips at depths and what is the rate of accumulation of strain in the crust in other words how close the crust is brought to failure by uh slip of the faulted depths the repeated Ultra precise measurements reveal that land here on the surface hardly moves at all this is a problem because deep underground the stresses and strains are still building up the fault is moving at depths at a fairly high speed and this deformation is growing and growing and growing with Time Miles underground the Deep fault is moving at more than an inch a year which tells fialo that in the centuy since the last quake the surface should have shifted 300 in 25 ft or more but it hasn't so sooner or later something's got to give and fialco knows what that something will be the Rocks themselves and one example is this type of rock which is called Granite this is in fact the rock out of which most of the Earth crust is made a microscope reveals the crystalline structure of the Granite the crystals make the Rocks tough but they have a hidden weakness the bonds between them may suddenly crack under stress basically once this material solidifies uh it is able to uh um crack and be uh sheared on the fold surface and the brittle behavior of these rocks is what lies behind the physics of first Quakes granite rocks underly all of the San Andreas fault but right here the Rock's under greater stress than anywhere else because it's so many centuries since a major Quake occurred and now we're over the 300E limit and so it means that uh The Strain the amount of strain that has been accumulated on the fault at this point is very close to the maximum strain that this fault has ever seen through its uh geological record and this is a fold that is capable of generating great destructive earthquak fialco believes the coming Quake could be the big one that people have been talking about for years and the effects could be horrific because of the population density of Southern California when the last huge Quake occurred 300 years ago Los Angeles was just a tiny Spanish mission Community with fewer than 100 people now it's America's second largest city with almost 11 million people living in the earthquake vulnerable metropolitan area people who live in California probably experience a small or a moderate size earthquake every year few things moving in your house but it's really actually kind of fun there is no major destruction um people just go on with their life uh much bigger events on the other hand are quite a bit different story with the threat to Los Angeles becoming ever clearer the investigation is nearing its conclusion data from repeated GPS measurements in the desert reveal evidence that stress is building up while examination of the rocks of the crust show they may not take the strain for much longer all the evidence points towards a potentially huge earthquake building up in Southern California and New experiments suggest the coming Quake could be far worse than anyone had ever imagined there is new urgency in the investigation into the San Andreas fault as revealed by recent evidence compiled by 300 of America's most respected scientists they warn that Los Angeles will be devastated if a major Quake strikes along the southern section of the fault line while there hasn't been a major Quake for hundreds of years even small ones can still be deadly like the Northridge Earthquake which struck this LA suburb in 1994 rupturing along an offshoot of the main San Andrea's fault the Quake was only a magnitude 6.7 considered moderate on the scale of earthquake measurement but it still killed 72 people and injured 12,000 more and new evidence suggests Mother Nature might have a lot more in store for Los Angeles scientists have long known that earthquakes generate several distinct sets of waves they travel at different speeds each spreading damage and destruction out from the epicenter modern city buildings in earthquake prone areas like California are engineered to cope with such waves Now new research by geophysicist Professor arid rosakis suggests that the San Andreas may offer a new and even more deadly threat rosakis researches how earthquakes rupture along straight line faults just like the San Andreas where it approaches Los Angeles he creates his own mini earthquakes representing the San Andreas Fault by a hairline crack in a thick transparent block this special material shows up internal stress lines when it's lit by a laser and the earthquake is triggered by a tiny explosion 3 2 1 zero the load has dropped and the explosion was big enough that we even have a crack an ultra high speed camera capturing 10 million frames a second reveals a startling and newly discovered phenomen phenon this Frozen picture reveals stress lines speeding along the mini San Andreas in the milliseconds after the explosion the cone to the left of this Frame is a previously unrecognized type of shock wave racing along the rupture line from the earthquake Center on a microscopic scale it looks and moves exactly like the sonic boom produced when a supersonic aircraft such is Concord breaks the sound barrier because we also see M cones lines that are emitted from the Rapture tips as from the tips of moving airplanes and just like a sonic boom it can be dangerous in the same sense that we hear the sonic boom uh from the Concord you're going to feel the sonic boom from the Rapa the danger comes because many highrises just aren't built to cope with extra stress from this newly discovered type of shock wave so if you are an old building for example uh you'll take one W you will accumulate some damage and uh very soon after that you will get very strong ground shaking because of other types of waves coming also the highspeed ruptures that Rak is called super Shear happen where faults run in a straight line which might help explain a 100-year-old mystery surrounding the great San Francisco Quake the natural disaster which launched the entire San Andreas investigation the overwhelming damage in San Francisco has long seemed surprisingly out of proportion to the 7.8 magnitude of the quake and there's a particularly straight section of the San Andreas approaching San Francisco so many scientists now believe that the damage was greater than expected because the 1906 Quake had traveled at Super sheer speed of Greater concern to Modern Emergency Services is not what happened a century ago but what could happen tomorrow because there is a similar straight section of faulted ground heading straight towards Los Angeles and if a super sheer earthquake develops on that line then the consequences could be disastrous all of the investigation warnings about the San Andreas came together in the fall of 2008 with the biggest earthquake drill ever held in California if this earthquake would have happened in reality there's would have been buildings coming down we know that there would be no water now in certain areas that's what this exercise is all about but what are the real chances of Los Angeles soon being hit by a massive earthquake frighteningly the best scientific consensus now warns that there's a 99% chance of a major quake in Southern California within the next 30 Years to better understand the threat to La the geologists produced their study jointly with experts in charge of the city's disaster planning and none of them doubt that the big Quake is coming it really isn't even a question of if anymore the shaking is going to be severe for 2 to 3 minutes and then it's going to stop and then you're going to have that moment of silence that often happens before you start hearing the car alarms and all those other sounds that you have in a disaster like this the study estimates that a major earthquake in the LA metro area would cause 2,000 deaths 50,000 injuries and2 billion of damage you're going to have configration developing tens of blocks will be on fire the water lines have ruptured there is no water coming out of the fire hyd that's the kind of nightmare scenario that we're looking at this Spectre of disaster to California's people and cities motivates the search to unravel the secrets of the San Andreas fault all the evidence is finally in the damage reports from the 1906 disaster show the false 800 mile path the different types of rock at muscle Rock provide clues to how the fault was created 20 million years ago the river bends prove how fast the land is moving the mineral to explains why some parts slip without major Quakes the brittle granite rocks reveal a threat to Los Angeles and recent lab experiments uncover new and more dangerous earthquake shock waves but one goal has eluded The Rock detectives who study the greatest fault line on Earth when will the sleeping San Andreas come to life once again it could be any time the only certainty is that nothing is certain in the ever evolving story of how the Earth was made Earth a unique Planet restless and dynamic continents shift and Clash volcanoes erupt glaciers grow and reced Titanic forces that are constantly at work leaving a trail of geological Mysteries behind one of these Mysteries is centered here in the Grand Canyon in Arizona close to a billion tons of rock have been carved out of the ground ground the canyon left behind could hold all the river water on Earth and still be less than half full for more than a century scientists have debated how and when this vast Chasm was created and now geologists are uncovering fresh evidence of how the Grand Canyon fits into the ever evolving story of how the the Earth was made the Grand Canyon one of America's most spectacular natural wonders a canyon 18 M across at its widest point 277 M long and more than a mile deep it is so vast that it can even be seen from space although Hell's Canyon in Idaho is almost half a mile deeper and Australia's Caper T Valley is nearly a mile wider the Grand Canyon Remains the most famous of them all and it also holds one of geology's greatest Mysteries just how did the Colorado River only a tenth the size of the Mississippi form such a large Canyon the answer has eluded scientists for more than a century because many of the clues they normally rely on have been swept away by the river's water over millions of years or buried by landslides or destroyed by volcanoes it seems like we should understand perfectly how the Grand Canyon formed the problem is we've lost a tremendous amount of evidence it's like a murder mystery where most of the evidence is lost and so the best we can do is piece together the evidence that we have even so slowly but surely this geological icon is giving up its most ancient Secrets the Canyon's richly colored layers offer scientists one of the most complete geological records on Earth the first concept you have to get your mind around as you're thinking about the Grand Canyon is that the stories told by the rocks are exceedingly old millions and billions of years carlstrom and his team are setting out on a grueling geology field trip along the Colorado River it won't be an easy ride because this 1450m long river packs a punch more than 800 million gallons of water can flow down the Colorado every hour more water every second than the average US household uses in a year carlstrom is investigating the ancient history of the land that was here before the Grand Canyon even existed and for that he needs to identify its oldest rocks he is following in the footsteps of pioneer Explorer John Wesley Powell in 1869 he was the first man to successfully ride the Colorado through the entire length of the canyon all of us who work in the canyon as scientists admire John Wesley Powell immensely for his Pioneer and scientific exploration of the Grand Canyon and the questions that he framed are still questions that we work on today one of Powell's discoveries was these intimidating black rocks at the very facee of the canyon well we're deep in the Grand Canyon right by the Colorado River you can see these spectacular black rocks actually John Wesley Powell called them uh ugly black rocks because for him these hard rocks made bad Rapids and that was harder on his trip but for those of us who are interested in the early history of Grand Canyon these rocks are the Bonanza Powell had no way of dating these rocks now identified as Vish new shist all he could conclude from their appearance was that they had once been molten deep underground but carlstrom has an advantage modern instruments that can accurately date the rocks by measuring radioactive decay and the first step in figuring out what happened here in the ancient past is to record when these rocks were created these rocks are about 1 .7 billion years old it's less than half of the age of the Earth so we have a great story here in the Grand Canyon of the last Almost 2 billion years of Earth history but carlstrom needs more information and these ugly black rocks hold another crucial clue to what this land looked like before the canyon was cut they can tell him not only when they were formed but also precisely how deep in the earth's cross trust they were made these tiny Stones embedded throughout the ancient Boulders are literally Jewels garnets that only form under immense pressure the sort of pressure that's found when layers are crushed by the weight of millions of tons of rock on top of them the Silver Bullet clue is the garnet these garnets are the key to understanding the amount of Rock Rock above us by analyzing the chemical structure of the garnet in particular its calcium content investigators can determine how much weight of rock was crushing down upon it at the moment it was made in simple terms if you analyze the garnet and you see higher calcium uh content of the garnet it means you're deeper into a mountain B more rocks above you so we take these garnets back to the laboratory we cut a very thin section we put them under an electron micro probe and the scientific result after this analysis is that we were 6 mil deep beneath the surface of the Peaks which were above us and that's a long ways so nearly 2 billion years ago before the canyon evolved ancient mountains 6 m above sea level stood here towering Peaks as high as the modern Himalayas over the next 500 million years these mountains were worn Away by the Relentless forces of erosion over Millennia the freezing and thawing of ice cracked open the rock of the mountain slopes wind and water carried the rock debris down towards the oceans leaving behind a flat and featureless plane with no sign at all of a canyon geologists learn to visualize the way that this place looked in the past knowing how to read the texture of the rock the kind of rock it is the fossils that are in it geologists can it's like a detective story you can uncover what this place looked like billions of years ago this is now desert country more than 300 mil Inland and yet these shells encased in solid rocks are ocean fossils in this one Cliff you can find fossil shells that look like you'd be picked up on the seashore today they die they fall to the bottom of the seafloor and they get trapped and die in the mud at the bottom of the ocean at the time that they're being deposited shells like these come from shallow tropical waters and Inland Sea that first arrived here half a billion years ago and covered the flat low-lying plain but that did not happen just once many different layers in the walls of the Grand Canyon tell carlstrom that over hundreds of millions of years this land has been submerged by the Sea not just once but at least eight times the last time this part of Arizona was under the sea was around 80 million years ago as we go higher in the layers in the Grand Canyon we have different age Seas which are depositing different kinds of rocks different environments different fossils that live at the different times this chapter of seas coming in and seas going out is itself hundreds of millions of years each sea deposited different types of material that hardened to become Solid Rock some sediment was sand that became buff colored Sandstone some was mud that hardened into darker Shale while the calcified remains of marine organisms were crushed into light colored Limestone and yet the dominant color is red that comes from Iron locked within all the Rocks over millions of years the iron rusts into a distinctive red Hue for the geology detectives descending into the Grand Canyon is like traveling back in time the C calcium content inside Garnet gemstones reveals that nearly 2 billion years ago mountains the size of Mount Everest stood where the Grand Canyon is now sea fossils exposed in the cliffs show that as late as 500 million years ago the land was the Muddy Bottom of an ancient Inland Sea the next puzzle for geologists is uncovering which awesome forces trans formed that unremarkable flat land into this breathtaking natural wonder of the world from 1.7 billion years ago to 70 million years ago the landscape of Western Arizona has undergone a series of extraordinary changes ancient mountains have given way to prehistoric Seas which have withdrawn to reveal a low-lying flat plane stretching as far as the eye can see the Magnificent Gorge of the Grand Canyon does not yet exist but over the next 20 million years this landscape was to undergo immense changes that would create a unique High plateau and set the scene for the formation of the canyon ancient fossils of sea animals tell geologists that this land was once under the waves of an inland ocean but that leads to yet another mystery the investigation needs to figure out why these undersea rocks are now high in the air thousands of feet above sea level it's surprising to go up a mile above sea level and you find a clamshell or what looks like a clam clamshell and you say I that's what I see when I go down to the ocean so why is it here a mile above sea level it's clear that this region underwent a type of geological disturbance that pushed up the entire seabed geologists discovered in the 1960s that collisions between separate plates of the Earth's crust could force land up into the air it happens all over the globe and usually deforms the land into tilted mountain ranges but this Arizona uplift was unique after all the flat layers are deposited in that sea level there was a major uplift event called the larid orogy which lifted these rocks without tilting them still flat lifted them up to high elevation because the land Rose straight up like being in an elevator it formed a high smooth Plateau the sea that had been there drained back toward the Northeast but as of yet there was no Grand Canyon the Colorado River the force that cut the Canyon from The Rock had yet to [Music] arrive geologists from the very early days from the late 1800s are quite comfortable with the knowledge that the Colorado River has carved the Grand Canyon the high Plateau was surrounded by even higher mountain ranges New Rivers began flowing from the mountains out across the plateau it's essential for the investigation to establish when the Colorado River in particular arrived because only then could it begin to carve the canyon until a few decades ago some investigators thought this ancient riverbed called Hindu Canyon provided the answer they believed that Hindu new Canyon's creation 50 million years ago marked the arrival of the Colorado River and the beginnings of the Grand Canyon but in 1969 the discovery of these Pebbles turned everything that geologists thought they knew about the canyon on its head it turns out that to explain how the Grand Canyon got there is very much more complex than people thought so the early geologists thought it was simple but now we realize there's a lot more to the story and it's kind of a detective story you start out with a few Clues and you put the clues together and then finally you get the satisfaction of saying well you know I figured this out before anybody else did figuring it out before anyone else was just what Young did in 1969 when he was a 24-year-old geology graduate student at Washington University his professors sent him to investigate Hindu Canyon but when young arrived at the dusty riverbed he discovered that it had nothing to do with the Colorado or the Grand Canyon itself his Discovery flew in the face of all the established geological theories and revolutionized thinking about the Canyon's history the evidence young had uncovered was the alignment of pebbles in the bed of the river if you look at these Pebbles you can see that the the Pebbles are flowing or the Pebbles are oriented in this direction which is a stable direction for water flowing to my right if the Pebbles had been oriented this way the water would have flipped them over so when we find Pebbles that are oriented this way that tells us that the water was flowing to my right it is a crucial clue the Colorado River could never have flowed to Young's right it has always run in the opposite direction towards the the Pacific Ocean the river here 50 million years ago was not the Colorado and it did not cut the Grand Canyon Young's findings meant scientists had to rethink all their ideas about when the Colorado had arrived on the plateau and about the age of the canyon they started examining evidence from another less ancient site this is Muddy Creek near Lake me Arizona just a few miles Downstream from where the Colorado River exits the Grand Canyon [Music] today the underlying rocks prove that this was once the site of a vast freshwater lake the upper part of the mudy creek formation is this nice Limestone which formed in a freshwater lake uh the water would have been very clean there would have been lots of plants and animals living in the water and as they sank to the bottom the calcium carbonate in their shells would form this Limestone which is typically what forms a limestone Rock the limestone is the calcified remains of the creatures that once lived in this Lake then 5.5 million years ago the animals all disappeared there were no shells to make fresh Limestone the only explanation is that the animals died 5.5 million years ago because that was the date when the Colorado River arrived here the river would have been carrying masses of dirt and rock sediment from the fledgling Grand Canyon the water would have been too muddy and dirty and Limestone does not form in dirty silty muddy water it's just incompatible the animals and plants that live in such a lake can't exist if there's a lot of silt and M mud in the water so the muddy death of the lake gave geologists a confirmed date for when the Colorado arrived in Arizona and commenced its excavations the Grand Canyon was born a mere 5.5 million years ago the investigation has reached a significant Milestone it has discovered the age of the canyon the angles at which Pebbles lie in ancient riverbeds reveal that the Grand Canyon is far younger than geologists had previously ever suspected the Limestone discovered at Muddy Creek reveals the date that the Colorado River arrived on the plateau and the true age of the canyon 5.5 million years old now geologists had a new mystery to solve discovering why the Colorado River took the path it did some 5.5 million years ago and why it carved a canyon of such remarkable Dimensions the investigation into the history of the Grand Canyon has uncovered a 1.7 billion year old landscape that has evolved from ancient mountains through to the Colorado Plateau 5.5 million years ago the Colorado River began carving out the Grand Canyon from this Plateau the question scientists now had to answer was what happened at that time to cause the river to dig deep and carve out the canyon it is a debate that has been going on for more than a century and which continues today I got interested in the Grand Canyon when I went to school and uh started studying and I heard about the different ideas associated with the Grand Canyon and was just blown away when I found out we did not understand how the Grand Canyon formed something as iconic as a Grand Canyon wasn't understood just seemed crazy to me and so basically decided to dedicate a large portion of my life to trying to figure it out one theory is that several ancient Rivers merged and their combined cutting power started digging out the canyon another assumes that the river cut down into the plateau as the land uplifted around it but John Douglas has his own Theory one that has gained respect among many leading geologist since he first published his ideas in 2000 what Douglas calls his spillover theory seems to work well on paper spillover is incredibly easy all it means is the colar river uh poured into a basin when it poured into that Basin it had to form a lake this Lake was huge all that Lake had to do was rise and then spill across the plateau it poured down cutting rapidly and over time you would have ended up with the beginnings of Grand Canyon very quickly at his college campus in Phoenix Douglas is building a scale model experiment to see if his spillover theory actually works in real life he sculpts tons of dirt into a model of the Colorado Plateau running faucets represent the flow of the Colorado River into the ancient Lake now we have our large lake the water's getting higher it's getting ready to spill across we have a tiny little trickle of water pouring down off the lake that little tiny trickle of water doesn't seem like much but over time that little bit of water flowing down that steep slope is going to gain energy it's going to start cutting making waterfalls that work their way back one water fall has now reached the lake you can see that we have just released a significant amount of water much more water than was previously pouring down now we have huge Canyon cutting landslides are sloughing off the side of the canyon walls the water flushing it Downstream the lake you can see that it's starting to shrink in size that lake is getting lower and right there you can see that we've cut our own small scale version of the Grand Canyon Douglas's experiment proves that the spillover theory Works in miniature but he needs evidence to show that it could have happened on an infinitely bigger scale Douglas sets out in search of a lake large enough and old enough to be the source of his spillover flood he has a prime suspect in mind this is the site of the ancient Lake bidahochi 100 Mil to the east of the Grand Canyon and a clue here on the old lake bed reveals how deep this Lake once was these green Clays which indicate deep lake water this is the classic evidence for the giant Lake necessary for the Overflow explanation of Grand Canyon these green deposits are only created in one specific environment to have Green Lake Clays you need deeper water where there is little oxidation I think that's indication that the color River has arrived in this Basin that it's made its way from the Rocky Mountains to this location and this is it basically stopover point before it eventually spills across to form the grand Canon establishing the depth at this point lets Douglas work out how large an area was once covered by water he compares the depth of the water with the Contour height lines of the surrounding Countryside and that shows that Lake bahoi once spread over 20,000 Square mil and contain more than 3,000 cubic miles of water that makes it bigger than Lake Michigan Douglas needs to date the age of this Lake for his spillover theory to work it has to be older than the Grand Canyon more than 5.5 million years he unearths the proof he needs in these deep water fossils okay these fossil shells are freshwater molus uh maybe as young as 6 million years old the dates match up the lake was here at the right time to have spilled over and begun cutting the Grand Canyon dating the fossils helped confirm Douglas's belief but his search for more evidence continues in reality we're never going to know how it Formed to 100% certainty unless someone builds a Time Machine by doing this kind of work all you're trying to do is increase your level of confidence on on your ideas build up your case build up your evidence building up his evidence is exactly what Joel Pon is doing he is using the very latest technology to prove exactly how fast the Grand Canyon was carved he has found the evidence he needs right here at the very start of the Grand Canyon here at least fairy there are all of these gravels that are evidence of Where the River has been in the past and the path that has taken during incision and amongst the gravels sometimes you see these great lenses of sand and we can use the sand to get an absolute date on these [Music] deposits as the Colorado River carved out the canyon it deposited more and more of the gravel and sand debris at this spot newer layers buried older layers over millions of years and geologists now have instruments that can measure how light has affected individual atoms within the sand that reveals precisely when each sand layer was originally buried away from the light of the Sun for the technique to be accurate it's essential that the sample is not exposed to daylight so here we can uh take a metal tube and we can hammer it into the sand outc crop and in the metal tube then we'll get a sample of the sand and it'll stay out of sunlight and then we take it back to a dark room laboratory and remove the sand uh still sheltered from light and then we can analyze the optical properties of it to get an absolute age um and in this case the absolute age would tell us when the river was at this point in the [Music] landscape back at the lab Pon Compares multiple sand samples each from a different depth in the canyon deposits discovering the age of each individual layer of sand lets him estimate how rapidly the river has been cutting down through the Rocks here at Le fery we can use this last half a million year history along with our absolute dates and all the information we get and uh and the rate of Canyon cutting here is about 1,000 ft per million years that's 1T in every Thousand Years a little more than 1 in every Century it proves that the entire 5300 ft deep Grand Canyon could have been cut in a little more than 5 5 million years in geological terms the mere blink of an eye the investigation is assembling evidence on how the Grand Canyon was created green clay deposits support the theory that an ancient Lake was big enough to spill over and Trigger the Canyon's creation deep waterer fossils prove that the lake existed 6 million years ago the right time to have overflowed and cut the Grand Canyon but proving how the canyon cutting began is only part of the investigation this is one of the widest and deepest canyons in the entire world and to discover how it grew so large geologists will have to examine some of the most dramatic and dangerous features the canyon has to offer the landscape of Western Arizona has transformed from ancient mountains to prehistoric Seas to a flat uplifted plain just 5.5 million years ago the Grand Canyon was cut through this Plateau it happened so fast that geologists had to think again about the awesome power of the Colorado River it cuts through Rock not by the water wearing it away you could pour water over Rock for a long time and nothing would happen it's the tools that the river carries the river carries Boulders and sand and those bump against each other and they eat away at the Rock every day the Colorado can carry almost 500,000 tons of rock and debris enough material to fill more than 100 Olympic swimming pools that is 5 tons every second so investigating River erosion is never an easy task because the powerful flow of the Colorado River has scoured and washed away many of the clues that The Rock detectives need they looked for evidence in the hundreds of Rapids that disrupt the river's progress the swirling Rapids are created when flash floods sweep Boulders into the river from the many smaller side Canyons the river has to focus a lot of energy at these points to deal with all of the boulders that are coming in the more coarse Boulders and more resistant material that the river has to fight against to accomplish its incision the uh the steeper it gets as the water flows over the Rapids it cuts deep into the Bedrock below at this set of Rapids alone the river drops 10 ft and there are a lot of Rapids on this section of the Colorado so it put all these Rapids together in a string through Grand Canyon and that gives you the the overall sort of unusually steep uh Grand Canyon profile of the river going through it gravity and simple physics are at the heart of how the Colorado has carved so much Rock so quickly 5.5 million years ago the Colorado River was flowing over the Steep edge of the plateau that had been pushed up thousands of feet above sea level the river ran rapidly over the Steep downward slope and swept rough Rocky debris along in its wake an incision formed digging back into the edge of the plateau the power of the river to in size as it dropped off that huge escarpment must have been really great and so the river quickly incid there and that very steep drop off of incision would have worked its way back Upstream through the Grand Canyon region it's sort of a waterfall that a few million years later has spread itself out through the length of the river it is this steep drop off between the Colorado Plateau and the land beneath it that fuels the Colorado's incredible erosive power the river begins its life high in the Rocky Mountains in Colorado for every mile that it travels the River Falls 10 ft by contrast the Mississippi River a rer moving 10 times as much water as the Colorado meanders across a flat landscape with no steep slope to drive it the Mississippi can't carve any Canyon but the Grand Canyon is not just steep it's also [Music] wide and here on the south rim at the heart of the national park the true m Majesty of the Grand Canyon is revealed this is where the canyon is at its widest as much as 18 miles from rim to rim this landscape appears Serene now but its unique beauty was forged by violent forces Grand Canyon often times we just associated with the car River the car river is what cut the Grand Canyon it it it formed the initial gash to allow the river to flow across but what makes Grand Canyon Grand is really its width and all the layers of rock that are exposed and that uh isn't only solely tied to the Colorado River what's happening is this rock that's exposed it's being beaten on by rain and the rain gets in there and it weathers a rock and it weakens it and then because this is so incredibly steep gravity will act on that material transporting it deeper down into the river flushing it back out and that process just repeats over and over again to allow the cannon to get wider over time we we have classic rockfalls that are cascading down onto the Black Rock in the far distance those events are indications that this is actively ongoing uh Canyon widening and retreating um from these processes the fall of these rocks is not a gradual process this is erosion at its most violent very few people are ever going to see Grand Canyon actually change like I've spent numerous nights in Grand Canyon I've only heard one or two rocks ever fall but change will happen and when it does happen it happens very rapidly the Rocks fall because both harder and softer rocks are layered one on top of the other in the canyon walls the harder layers are made of limestone and Sandstone these rocks don't weather easily but the softer Shale beneath is made of mud that expands when it rains causing the the Shale to crumble away those weaker rocks they weather and Retreat back and they undermine the resistant Cliff rocks above that will then fail as dramatic rockfall Landslide events allowing the canyon to increase its width The Rock Falls are merely the first step towards increasing the grand Canyon's enormous width without the help of an accomplice the entire Canyon would fill up with debris without the C River you could not have the Grand Canyon as wide as it is by flushing that material Downstream it like it wipes it all clean to allow a whole new material to build up again and once you repeat that over and over again it allows the canyon walls to retreat back and the entire Canyon just grows these guys continue to March and push and move all that material down stream the mystery of how the Grand Canyon grew so deep and so wide is being solved the Colorado Rapids demonstrate how the steepness of the riverbed helps carve the canyon so quickly rockfalls on the canyon walls reveal how weaker rocks rapidly widen the canyon Across The Plains of Arizona but this is far from the end of the Grand Canyon story in just the last million years the canyon has been transformed by other overwhelmingly powerful Natural Forces geologists have established that over 1.7 billion years the Grand Canyon emerged from ancient ient mountains and prehistoric Seas to become one of North America's geological icons this is a rare look at one of the most remote and secret parts of the Grand Canyon a series of small cone-shaped mountains line the Canyon's Edge and there are flows of black rock running down from each rim they come from a remarkable era just 725,000 years ago when the piece of the canyon was shattered by volcanoes this is toro point in a remote area known as the Arizona strip one of the most isolated places in the continental US few people other than geologists ever see this area although it boasts some of the Canyon's most stunning views The Rock detectives come to see how explosive volcanic eruptions have Chang the canyon in the comparatively recent geological past this black rock that seems to have spilled over the rim of the canyon is an ancient lava flow what was once boiling hot rock forever Frozen in Time Howell talked about a river of molten magma pouring down into a river of of melted snow and he talked about how dramatic it must have been the boiling and seething and the steam and and uh it it must have been amazing you you would picture red hot um Lava like you would see in Hawaii pouring down the canyon walls and coating them and then once it reached the river it would uh you know it would immediately uh create just giant clouds of [Music] steam the extensive lava flows erupting from as many as one 100 cinder cone volcanoes had a dramatic effect on the Colorado River Running below Crow believes that on at least eight occasions the volcanic eruptions created huge lava dams that blocked the river completely well behind me here is is one of many balt remnants um they're the remains of lava flows that poured down the canyon partially filling it and then subsequently the Colorado uh River has has removed all but a few little chunks the lava dams brought even the powerful Colorado River to a halt for a [Music] while in time the dams were no match for the Colorado the rising pressure of the Damned river behind them eventually became too much and they shattered [Music] this explosive episode has left its mark on the Canyon's walls today the cones appear to be extinct and lifeless although some geologists believe that the volcanoes might not be finished quite yet the last eruption that sent lava pouring into Grand Canyon probably occurred uh about a 100,00 years ago there is evidence for a uh an eruption on the on the rim that didn't actually make it into Grand Canyon that's a thousand years old so there's uh there's you know I think a a good chance that that in the future there may be eruptions here as well the grand Canyon's future has yet to be written but investigators Now understand the story of its past the calcium in the garnet discovered at the base of the canyon reveals the ancient beginnings of this landscape an immense mountain range limestone rocks show that the canyon was only formed 5.5 million years ago green Clays that can only form in deep water prove that a huge Lake bigger than Lake Michigan could have been the trigger for this Canyon carving and rock falls from the crumbling Cliff faces of the Canyon Rim are evidence of how the canyon grew to the shape it is today geologists have been studying the canyon since the mid 1800s yet even after More Than A Century of Investigation the story is still far from finished the landscape is evolving and it's going to be changing um through the geological future and so the story about the geology and the fascinating questions here is not one that's over and it's going to continue to evolve as scientists continue to do work here the dynamic geological phenomenon of the Grand Canyon is a place where the vast fiery forces within the Earth's crust do battle with the inexorable power of water the result a natural wonder whose walls record nearly 2 billion years of our planet's turbulent geological history [Music] Earth a unique Planet restless and dynamic continents shift and Clash volcanoes erupt glaciers grow and recede Titanic forces that are constantly at work leaving a trail of geological Mysteries [Music] behind this episode explores the Yan Valley a magnificent 3,000 ft deep Canyon traveling through time scientists are unlocking deep Secrets trapped inside these Granite walls these rocks have literally been to Hell and back Frozen drenched and battered by Earth shattering forces one more chapter in The Incredible story of how the Earth was was [Music] made in the foothills of the mighty Sierra Nevada California lies a valley like no other on earth yede a 7mile long 1 M wide Granite Canyon here lie some of the most awe inspiring geological features on the planet half America's most iconic Peak yane Falls the the highest unbroken waterfall on the continent and El Capitan one of the biggest sheer cliffs in the world the Europeans discovered this astonishing Valley only 150 years ago these sheer walls and Granite Cliffs High waterfalls was a Marvel to them as it is to us ever since it shot to fame Yus has been shrouded in mystery it's almost as if there was a higher power at work that basically said that looks really good right about there and then just put a little bit of grass right there and put some Oak like an oak Woodland right through there and that's it that's perfect because it doesn't seem like anything was halfhazard it seems like this was designed to overwhelm and leave people asru Yan's unique design has intrigued scientists for centuries I think when you see something that's this dramatic you just have questions and the question is how did this happen how do you get monoliths these huge stone structures that are just Rising thousands of feet off the valley floor how does that come to pass and for over a hundred years people have been trying to answer that question The Story begins in 1870 when amateur geologist John mure went hunting for the answer founder of the Sierra Club he funded his obsession with the valley by hering sheep and writing articles about yean he wrote that no Temple made with hands can compare with [Music] yane mure scoured the landscape for Clues as to how this unusual box-shaped Canyon formed and came up with a radical seemingly far-fetched theory he believed that the world's climate was once extremely different and the Lush Canyon where the Merced river flows was filled by a gigantic Glacier thousands of feet thick M proposed that as this River of ice slowly flowed downhill over thousands of years it gged a deep Canyon and sliced vertical Cliffs into the granite walls but that controversial idea brought him into conflict with a fearsome opponent the admired California state geologist Professor Josiah Whitney Josiah Whitney did not have much respect for John Mir because Josiah Whitney was a state geologist and at at that time John mer was hurting sheep certainly he's thinking what does this man know about this range how dare he Whitney believed that this unusually Square steep-sided Valley could only have been formed by a sudden cataclysmic event he was adamant that giant cracks in the earth caused the valley to pull apart and dramatically sink cleaving steep Cliffs as it fell This Bitter Whitney mure conflict raged on for decades but now scientists are hoping to figure out this complex puzzle once and for all the first stage of the investigation is to understand how the Rocks themselves were created the canyon is made almost entirely of yede granite one of the hardest rocks in the world to understand how this formed scientists must travel back in time time to the beginning it's 250 million years ago and the landscape is very different dinosaurs roam the land and dominate the skies an incredibly rare remnant of that time has been discovered Northwest of the valley at Mount Hoffman this patch of softer reddish rock is the oldest in the park [Music] it's sandstone and it once covered the entire region this rock is very different than most of the Rock in yed it's much darker in color it's got a different texture this was originally a sedimentary rock that was deposited in layers on an ancient Shore sand and sludge compacted together and over millions of years formed this Sandstone this tranquil landscape was transformed by an earth shattering event deep deep below the surface and the evidence lies here in the Rock here we have this older layered sedimentary rock you see the many layers and banding which continues across over into here but strangely this section of granite is cut right through the sedimentary rock and split this section in two how this unusual rock formation formed can be explained by a simple experiment using sand and wax this red wax here represents the granite the sand represents sedimentary rock and right now I'm heating it to see what's going to happen when the wax melts actually I start to hear some of oh here it goes we're actually getting a little bit of the wax pushing up through the sand and the molten wax is lighter and so it's pushing its way up through the sand which represents the sedimentary rock yep there's some more it proves that the only way Granite could have cut through this Sandstone is if it was originally molten and able to flow like a liquid molten rock forms deep within the Earth Rises up through the crust in this case forced its way through a crack expanding it open and then Cooling and solidifying to form this band of granite this band of granite tells scientists that y's Cliffs were once molten and heated to 1800° f 95% of the Rock in Yus is granite and I can see with a naked eye all the crystals in here they're fairly large and that tells me that this rock cooled very slowly scientists were now on the hunt for what was generating all this molten rock the investigation LED them to mount Gibbs another unusually colored mountain in the northern reaches of the park it lies above a layer of granite and is made from reddish gray [Music] rock strangely these rocks were also once molten here I have a rock from Mount Gibbs and I can see that most of the crystals are very very small most of them I can't even see these small crystals tell an incredible story when molten rock cools quickly in the open air crystals don't have time to grow what that tells me is that this is a volcanic rock that was spewed out at the surface it is 200 million years ago volcanoes shattered the Tranquil West Coast the Earth explodes with molten rock for the next 100 million years lava pours thick and fast onto the land covering the sandstone in volcanic rock 10,000 ft High it stretches for 400 miles along the coast North America's greatest mountain chain the mighty Sierra Nevada is forming and the area that would become yusan is caught right in the middle of it but some of this Rising molten rock never makes it to the surface trapped beneath the blanket of mountains it cools slowly creating a giant chamber full of solidifying granite 2 miles below the surface 400 m long 60 M wide and 5 m deep it stretch es along the entire spine of the Sierra Nevada mountain range y's immense Granite monoliths were forged in a fiery furnace 2 miles below ground 100 million years ago I would have been standing in a vast chamber of molten rock with rock Rising thousands of feet above me scientists investigating how the rocks at yeus formed have found bands of granite evidence y's rocks were once molten and volcanic rocks proof that the granite formed deep beneath the Earth but scientists were still mystified yeeman Granite is so strong it's unlike Granite anywhere else on Earth for hundreds of years they tried to solve the mystery while the answer was actually staring them in the face 250 million years ago ye's landscape was a peaceful Coastal [Music] plane now the investigation moves to 100 million years ago the land that would become Yee is in turmoil volcanoes dot the skyline spilling mountains of lava onto the land and in tunb beneath 2 miles of volcanic Rock lies y's molten Granite the next 10 million years is a critical period for the rocks of yede something unique is happening to the Granite making it tough enough to hold up Cliffs 3,000 ft High the search for the secret of Yus granite's immense strength LED scientists to the biggest steep-sided Granite Block in the world the mighty El Capitan twice the height of the Empire State Building over 3 billion cubic feet of rock Rises into the [Music] air El Capitan is the largest Granite monolith in yede National Park 3,000 ft a pure Granite it's one of the biggest cliffs in the world when I look up at something like this I really want to hang onto the rock because I feel like I'm going to fall backwards with vertigo amazing elcapitan is the ultimate big wall climb once considered impossible to conquer it's a treacherous Ascent up a vertical near featureless rock face with only a handful of roots to the summit sheer Granite walls are normally unstable and over time get pulled down by erosion so it was a mystery how rocks could hold up Cliffs this big scientists are sampling the rocks to find out but the ye Granite doesn't give in without a fight these y granates are really hard you can work up quite a sweat trying to collect a bag full of this stuff buried within this rock is the secret to Yus granite's success oh finally well one clue to why these rocks are so tough is given by this sample right here these are really large crystals large crystals make a rock really strong they kind of weld together and they're Flawless and they give a rock a lot of strength but it was a mystery how these tough crystals got so large and created such Flawless rocks this is in contrast to normal Granite which when it cools forms a hard rock with a fatal flaw riddled with cracks these rocks are vulnerable to erosion if you take anything and it's very hot and you cool it quickly it'll shatter Granite bodies that cool quickly and form a lot of cracks that weaken the rock body and make it unable to support 3,000 ft Cliffs if you walk up to a typical granite and look at it you'll find cracks a foot apart 2 feet apart you walk up to El Capitan you might have to go 100 feet or more between cracks in the Rock clearly something different happened here 100 million years ago ELC Capitan is really just one large uniform essentially f L piece of granite and that makes it very difficult for erosion to deal with for many years it was a puzzle what had caused yeman Granite to form so differently but the secret had been staring scientists in the face one of the things you can see is a clue as to how this landscape form in that dark diagonal splotch that's called the North American wall because that dark blob looks like with some imagination a map of North America and you can kind of see Baja California sticking down on the left side there in Alaska up to the Northwest and it's made up of a much darker finer grained Rock like this this dark Granite is not just a map of North America it's a window into the unique events that happened inside the Yus Granite when it was buried deep beneath the Earth and it's a younger body of granitic rock that filled a crack with within the main body of ELC Capitan Granite 100 million years ago the main body of granite cools and begins to harden beneath the Earth but then fresh molten rock invades a crack and injects it with a blast of heat the granite now takes 10 times longer to cool huge robust crystals form and reeal the defective cracks time after After Time Fresh molten rock invades old remelting and Welding the yede granite creating gigantic shatterproof blocks which now Tower thousands of feet into the air given that these are obviously very strong rocks it it puts the Whitney Mir controversy in an interesting light because Whitney wanted the rocks to have broken and for the valley to have fallen down in between a couple of major cracks Mir wanted the whole thing to be carved by glaciers and both of those seem really difficult given how strong these rocks are and yet behind me here is a 3,000 ft deep valley something carved [Music] it in the search to understand why yemane Granite is so strong scientists have found large granite crystals welded together to form a tough tough Flawless Rock and the North America wall evidence that yeus Granite was reheated Time After Time creating huge faultless blocks 100 million years ago ye's Granite lies buried beneath a volcanic mountain range 2 mi High Rivers slice into this soft volcanic roof gouging and washing it away then 60 million years ago when dinosaurs are no more the featureless lump of ye Granite is finally exposed to the elements but ye's Ultra tough granet defies attack for another 50 million years it remains unscathed it would take a catastrophic event to Chisel the 3,000 ft Canyon out of one of the toughest rocks on Earth Yan's mered River me Anders in a 3,000 ft Canyon but 250 million years ago no vast Canon stood here Yee is a flat Coastal plane it is blasted by volcanoes and its Granite is buried beneath 2 miles of volcanic rock when the Yus Granite is finally exposed it is a shallow runof-the-mill River Valley for a staggering 15 million years it defies the destructive powers of erosion if scientists were going to solve the mystery of how y sem Valley formed they'd have to investigate the pivotal moment 7 million years ago when a 3,000 ft Canyon was suddenly chiseled into the granite one of the toughest rocks on earth a clue to what Almighty Force overpowered the yean granite lies high up on the exposed Cliffs strange deep cracks running for hundreds of feet through the rock y's granates are strong but they're not always strong I'm standing on a fin of rock between two deep fissures these cracks run right across the yosd landscape and they clearly formed after the granite formed and if I look at their orientation they all go to the Northeast strangely yane Valley is also oriented along the same Northeast southwesterly Direction perhaps these cracks were the remnants of a cataclysmic rock splitting event as Josiah Whitney had predicted a respected Yale educated scientist he passionately believed Titanic forces beneath Yee had pulled the land apart causing it to collapse along gigantic Faultline cracks could it be that the argument was swinging in the bombastic Whitney's favor and M's glacial theory was the rambling of an ignorant Shepherd after all scientists searching for the answers as to how these giant cracks formed used modern technology to take a closer look at the ground beneath the Sierra Nevada they did not find evidence of Whitney's cataclysmic rifting Valley but discovered a catastrophic event which had ramifications on a far greater scale seismic evidence has revealed that the Earth's crust is made of layers the lighter outer shell forms the land but fastened beneath is a dense anchor of sturdy Rock and beneath the Sierra Nevada scientists discovered something extraordinary a huge section of this lower crust 200 M long and 40 m wide is missing this model represents the Sierra Nevada as it looked 10 million years ago so the top here represents the mountain range the bottom there it represents the lower crust sometime in the past 10 million years part of that lower crust disconnected from the mountain range and dropped away the end result is that there was uplift of the Sierra Nevada because they were being held down by those dense rocks so there was uplift of the Sierra Nevada but because most of the route fell away to the east the whole mountain range ra rather than bobbing straight up tilted to the West 7 million years ago a huge chunk of the lower crust suddenly drops away the entire mountain chain snaps along its spine and tilts upward finally here is a force capable of overcoming Yan's Ultra tough Granite as it snaps the enormous pressure cracks the solid Granite along the entire length of the mountain range but it was a mystery how these cracks could give rise to a 3,000 ft deep Canyon scientists realized some other Force must have attacked the weakened vulnerable Granite the hunt was on for an accomplice and 5 miles Downstream of Yus at El Portal they find it Rapids here Yan's Meandering Merced River has transformed into a raging torrent at times 1,000 cubic feet of water gush through this narrow Gorge every second creating treacherous waves and turbulent [Music] edies so this is the Merced River about 5 miles Downstream of Yus Valley it's extremely powerful it's a series of Rapids and and Cascades over these Boulders and there's a lot of energy being expended by this river right now scientists realized This ferocious Force combined with the rock weakening cracks even had the power to cut into y's Granite the erosion of the river is focused right along the riverbed and so it will cut down like a saw blade into the Rock about the width of the river so as it does that it will come down and steepen the valley walls those those walls will become unstable and there'll be landslides into the river the river will wash away the material and uh you'll be back to that vshape scientists realized if the mered river created this deep v-shaped Canyon then it could also have cut a deep y Valley 7 million years ago as the Sierra Nevada tilts upwards the mountain slope gets three times steeper and the Western flowing mered river surges with a torrent of water like a saw blade it zigzags along the path of weakened cracked granite in less than 5 million years it cuts a 3,000 foot v-shaped Canyon running straight through the heart of yeus scientists investigating how ye's deep Canyon formed have discovered strange cracks in the Rock proof that the uplifting Sierra Nevada weakened the granite and Rapids Downstream evidence that the Merced River cut a deep v-shaped Yus Canyon but one part of the riddle remained unsolved Yan's unique box-like shape some other extraordinary force had caused the canyon walls to collapse and the valley floor to flatten the controversy about how this strange Canyon formed raged [Music] on yede has had a turbulent past 200 million years ago its Coastal plane is Shattered by volcanoes and then 7 million years ago the meret river suddenly carves a deep v-shaped Yus Valley for the next 4 million years the river runs in this narrow Canyon but then yane is radically transformed again about 2 and A2 million years ago when our ancestors were beginning to evolve in Africa the vshape valley that was here began to evolve into the present valley floor which is flat and is bounded by these vertical sheer rock walls on its side it was during this second extraordinary stage of Cliff formation that the most iconic Rock in America formed Half Dome this natural wond unique shape has intrigued people for centuries its enormous Granite Dome is over 3 billion cubic feet in size as large as 1,000 football stadiums and its striking Northwest Face is a 2,000 ft vertical drop in 1870 amateur geologist John mure had a radical theory about how half doome and y's other vast Cliffs formed he believed that thousand of years ago the Earth's temperature had plummeted and the valley had been filled with ice you know one thing that's important to keep in mind about about John miror he didn't come up with his idea overnight he was trekking hiking walking going up to the tops of mountains and the entire time he was doing this he was listening he was seeing he was feeling he was touching and so he was slowly letter by letter word by word learning the language of yane mure knew from research in the Europe European Alps that glaciers were capable of gouging out Solid Rock as these great rivers of ice flow downhill they press down on the canyon walls with a weight equal to 200 trucks per square yard ripping out chunks of rock and causing the valley walls to get steeper in general glaciers transform a v-shaped valley that we see is characteristic of a river into a uset valley by focusing their erosion on the Valley walls rather than on the valley bottom until it has reached this U shape at which point it can then continue to erode as that U shape mure knew that as a glacier flows it grinds and polishes the Bedrock with rough shards of rock lodged at its base as they melt and disappear glaciers leave behind u-shaped valleys and distinctive scratch marks mure proposed that giant rivers of ice also once flowed through yusan Valley he hunted high and low for evidence of glacial scratch marks and eventually found a small 20ft square patch of Rock 30 ft from the valley floor the granite has scratches on its surface each one of these scratches is associated with a rock embedded in the sole of a glacier I can imagine mure claiming that this is irrefutable evidence of glacial occupation of the valley floor but if glaciers plowed down the valley why weren't there millions of scratch marks on the cliffs if mure was correct this is a picture of what happened 2 and 1/2 million years ago the temperature plummets yemane Valley fills to the brim with a gigantic Glacier only the tallest mountains Peak above the Sea of Ice for thousands of years the glacier grinds away at the granite walls scratching the cliffs and undercutting a peak that will become Half Dome when it Retreats the glacier leaves precarious slabs of overhanging rock the unstable rock face crashes to the valley floor cleaving the Great Northwest Face of Half Dome in the same way subsequent smaller glaciers cut away at the base of the valley for 2 million years cleaving sheer vertical Cliffs and removing all traces of glacial scratch marks but there was still one glaringly obvious problem with M's Theory and Archen enemy geologist Josiah Whitney pounced on it if glaciers had carved the valley why was Yus uniquely box-shaped and not u-shaped like a classic glacial Valley Whitney attacked M's Theory and stubbornly declared this square flat bottomed Valley could only have formed if the bottom had fallen out Whitney hypothesized that instead of being carved by glaciers that this was a fault-bounded valley with the valley walls being faults down which the Block in between the valley walls has dropped in Whitney's Theory the flat valley floor would be the top of the Dow dropped Block in the quest to unravel the mystery of Yan's flat bottomed Canyon scientists are investigating the valley floor the kind of sediment that I see in this Cut Bank are coarse grains Pebbles and sand the same kind of rocks and sediment that the present stream can carry in contrast to that the deposit I see at my feet is very fine grain light fine grain sediment like this is easily carried by flowing water but when a river hits a body of Still Water its energy levels slump and it dumps its load this is the kind of sediment that we would expect to see on the floor of a lake further research has found similar strin sediments all over yede it's proof that 10,000 years ago an ancient Lake drowned this entire Valley starting at the head of the canyon it stretched for 5 miles through the landscape but it was a mystery how Lake yede had formed scientists scoured the valley looking for answers and near the base of elcapitan at the farthest end of the valley they stumbled upon an insignificant looking Ridge it's an important clue to how Lake Yus and the valley formed this mound is made of an unusual collection of rocks and it runs from one side of the valley to the other given this Arc of a ridge is just down from elcap one might expect that it could have been caused from a rockfall but if you look around that's not the case clearly even in this local area we have rocks that came from at least three different places no doubt up the valley this pink Rock came from one portion of the valley this gray Granite came from another place and this particular one we can see the distinctive Feld spars associated with the cathedral Peaks Granite this strange distribution of rocks means that the ridge could not have formed from a catastrophic Rock fall some something else just as epic must have created it this is a Glacial Marine the remnants of a glacier which once filled the valley it's the conclusive evidence mure had hoped for morain form as glacial ice rips fragments of rock from the valley walls carries them like a conveyor belt several miles Downstream and dumps the rubble at the mouth of the glacier scientists realize this Ridge was also key to solving the mystery of how Lake yane and the flat bottomed valley floor formed it wasn't just a merine it was a giant [Music] Dam it's 2 and 1/2 million years ago and Glaciers grind through the valley 10,000 years ago the temperature rises and the glacier Retreats a huge huge Marine is dumped at the valley mouth damning back the icy meltwater the entire Valley floods creating an enormous Lake Yus Mountain Streams spill into this still water and dump ton after ton of fine sediment the lake chokes with silt creating Yan's distinctive flat bottomed valley floor we know from seismic evidence collected in the 1930s that it's 2,000 ft thick that's enough sediment to cover New York City by a foot and beneath this Lake of sediment they found the evidence that had always eluded mure a U-shaped Basin the Hallmark of a classic glacial Valley it was indisputable evidence that M's intuitive observations and seemingly far-fetched Theory were correct and the final nail in the coffin for Whitney's theory of a cataclysmic rifting Val Valley scientists trying to understand how the Steep Cliffs and flat bottom Valley formed have found scratch marks evidence that the sheer Cliffs were carved by glaciers and a glacial merine proof that an ancient Lake yede filled with sediment and created the flat valley floor for over 2 million years the glaciers Whittle away at yusan then 10,000 years ago the GLA Retreat for good leaving the one M wide Canyon we know today but strange dangerous forces are still exerting their powers on ye's landscape with catastrophic [Music] consequences yemane Valley has been sculpted by torrential water and thick slabs of ice but today another hidden force is shaping This Magnificent landscape it's 652 p.m. July 10th 1996 yeus is hit by a catastrophic rockfall within minutes a huge dust cloud of pulverized Rock engulfs the Valley News spreads that happy Isles the busiest Trail in the valley has been decimated y is in a state of emergency when I got here the devastation was really in full force I saw trees that were just everywhere the were ambulances and Chaos just was everywhere people were running around screaming and the whole area looked like a bomb had gone off 880,000 tons of rock had suddenly dislodged from The Cliff face the weight of 1600 trucks basically fell down it hit and then exploded and they created a wind blast as strong as a tornado the wind blast uprooted trees a half mile away from the Impact Zone we can have about 3,000 people go up and down that trail in one day and so we did not know how many people were trapped under the trees and tragically a young man was pinned by a tree and was killed and a young woman was trapped under a tree and is paralyzed a deadly mysterious force is continually at work in Yus causing the surface layers of the ultra tough Yus Granite to peel away in huge chunks one large rockfall occurs every week in the park and yet up to 4 million people visit Yus each year getting perilously close to these potentially unstable Cliffs to disc discover what's causing ye's incredibly tough Granite to fall down researchers have dotted vibration sensors and solar powered seismic stations all over yusei's Cliffs enabling them to listen to The Rocks this computer allows me to see what's going on all the time for example if I throw this rock at the cliff over there I just created a mini rockfall and take a look and these spikes are the rock hitting the cliff and then tumbling down this is a mini rockfall that happened right here so the station will pick up rockfalls that happen that are small right here but it'll pick up larger ones in other places this seismic listening device has pinpointed a recent rockfall behind Half Dome it's a chance for Valerie Zimmer to investigate why yusei's rocks are falling down and all the evidence indicates another cataclysmic event has occurred [Music] oh look at this all these trees have been knocked over like their toothpicks these rocks range from the size of a house to just dust analysis of the seismic data shows this was a massive rockfall one of the biggest in the last 20 years it shook the ground so hard it was the equivalent of a magnitude 2.4 earthquake if you look up on that mountain the amount of rocks that came down you know you look up high it doesn't look like a big area but it's deceivingly large it's probably the size of maybe 40 houses alog together strangely immediately above the scarred rock face a new dome is forming mysterious domes are forming all over the valley the most famous Half Dome glaciers cleaved its vertical face but its Dome top has been shrouded in mystery a strange underlying force is sculpting these Peaks into domes causing the rocks to Tumble [Music] down north of yeus on the Dome at Olstead point it's possible to get close enough to investigate why the surface layers of granite are shattering these stones are all over the place I see these layers running parallel to the surface they're almost like the layers of an onion and the layers are starting to peel off in fact look right here this one is coming apart the outer surface of the rock has fractured into layers running over the summit and down the sides of the Dome these are weaknesses in the Rock it's obvious that there must be some sort of force that's causing the rock to break in this way and peel apart like an onion the only Force capable of fracturing the ultra tough yeus Granite like this originates deep within the earth 100 million years ago the yean granite is beginning to form submerged beneath 2 miles of volcanic rock it's squashed and squeezed from every direction over the next 40 million years the volcanic roof erodes away way the immense downward pressure is removed leaving these Titanic forces out of balance the surface of the exposed yeus Granite is now an Avenue through which this pent up pressure can be released the granite is still being squeezed from the sides and from the bottom but at the surface it's free to move what happens is these layers start to open up parallel to the surface the release of this ancient pressure causes the surface of the Granite to fracture into onion layers which then peel away and so when the tops of those mountains fall off you're left with rounded domes but it's not just the Granite Peaks that are affected it's the cliffs too these layers will also form if the ground surface is vertical like a cliff creating vertical fractures alongside the cliff these vertical fractures allow the rock to then slide out and create rockfalls and this is one of the major contributing factors to rockfalls in yede y's catastrophic rockfalls are the legacy of its prehistoric birth beneath the earth 100 million years ago the gradual release of this ancient pent up pressure has created an untamed and dynamic landscape rockfall is a natural process and is part of the ongoing evolution of yean National Park I always get a little bit tickled when people ask me questions like like what are you going to do to prevent future Rock Falls it's a constant reminder that this is a wild place and that there's nothing we can do or should do to tame it in any way shape or form but it's something that after I'm long gone will continue to happen for the last 150 years scientists have been figuring out how This Magnificent Valley formed they found volcanic rocks proof that the molten GR cooled deep beneath the Earth large crystals evidence that yeus Granite cooled slowly creating tough faultless Rock Rapids Downstream show that the mered river cut a deep v-shaped Canyon and rocks carried by a glacier conclusive evidence that ice carved y's steep Cliffs and flattened its valley [Music] floor yede a valley of giants is a geological Masterpiece the unique strength of its near perfect Granite has created some of the most imposing and iconic Landscapes on planet Earth one where the deep Earth forces that created it are continuing to shape its future living proof that the Earth is never at rest
