The Secrets of Death Valley Uncovered | How the Earth Was Made (S2, E9) | Full Episode | History

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 behind and there is   nowhere more mysterious than death valley the  hottest and driest desert in the united states this is a place where even 700 pound  rocks appear to move by themselves it's the lowest point in the u.s and right  here the earth's crust is thinner than almost   anywhere else on the planet death valley  is a dynamic laboratory for investigators   who uniquely read rocks like x-rays to reveal  the inner workings of the earth and its history adding to the continuing story  of how the earth was made death valley is the largest  national park in the lower 48 states   more than three times the size of rhode island  straddling the border of california and nevada and   surrounded by towering mountain peaks 140 miles  long and up to 15 miles wide with temperatures   reaching a scorching 134 degrees fahrenheit this  is one of the most inhospitable places on earth but for geologists death  valley has a unique attraction   here they can witness the interplay of  the earth's most titanic geological forces   when you look at death valley really you're  looking at a battle a battle between processes   that are occurring on the earth's surface  and we can see the record of those forces of   nature locked into the rocks death valley has  an archive that is almost unrivaled worldwide to uncover death valley's earliest history brave  is hunting for its oldest rocks he is searching in   one of its most remote spots in the extreme south  of the valley in the isolated alexander hills   this is one of the oldest rocks in  death valley it's 1.2 billion years old   and given the color of this rock and the fact that  it's quite soft it can powder when i scratch it   these are all clues that tell  me that this is a limestone   the limestone is a major clue to revealing  the way this arid desert used to look   if we think about the type of environments   that limestones can be deposited in the first that  comes to mind is an underwater in a marine setting there is only one way to form limestone it is made  from the tiny bones and shells of sea creatures   they die and sink to the sea floor  where the weight of further layers   on top of them crushes them slowly into solid rock   and prave has discovered other startling  evidence that death valley had a watery past   fossils are a major clue they are vital in  the type of evidence that a geologist will use   these are some very nice examples of the type  of fossils you can find in these ancient rocks   and you can see here these curving  surfaces outlining what looked to   be large cabbages that are sliced in half  these were algae known as a stromatolite   ironically these marine fossils have  survived in the death valley desert   only because there is so little water  that might otherwise have washed them away   but they would have originally looked like this  when they flourished in the death valley waters as   the limestone formed more than one billion years  ago these tell us that the environment when this   rock formed would have been a shallow sea if i'd  been here when these rocks were first being formed   i'd be sitting in my swimming trunks about waist  deep in water very much like the bahamas today   the stromatolites are some of the earliest signs  of life on our planet to discover what happened   over the next one billion years prague studies  evidence in the surrounding hills the different   bands of colors and the rock layers and the hills  represent ancient seas that covered the death   valley area the seas would deposit a layer of  limestone move back across the land another layer   of limestone would be deposited and so we have a  history of the seas moving across the death valley   region from the time of the stromatolites to these  rock layers now more than a million years later geologists wanted to figure out what dramatic  geological upheaval could have turned death   valley from a shallow sea to the baking hot  desert of today and brave has found clues   in a rock that is entirely different from the  marine limestones he has studied up until now this is a nice example of a  rock type called a granite   and it forms those veins that  are in the hillside behind me you can think of these like the fingers of my hand   they're fed upward from a much more larger  massive area of granite sitting underneath   the granite tells scientists the reasons  why death valley's ancient seas vanished   today it is solid rock but it was once  hot molten magma from deep underground only one force of nature has the awesome power   and 2000 degree fahrenheit heat to melt  rock into magma and fire it to the surface volcanoes the seas here didn't just drain away  they were pushed back by these mountains of fire it was only in the 1960s with the realization that  earth's continents were drifting around the planet   that scientists figured out why the  volcanoes erupted under death valley the theory of plate tectonics revealed  that around 100 million years ago   an ancient oceanic plate began sinking  under north america pushing up the land heat from the collision powered a coastal chain  of volcanoes erupting on the land and finally   driving away the seas submerging death valley  this landscape would have been very explosive   a hostile type of setting and that then set  the stage for what was to become death valley still surviving in the valley  to this day is the ghost town   evidence of another substance far rarer than  granite that the volcanoes brought to the surface gold although gold occurs naturally  in more than 30 different u.s states   the golden death valley was concentrated in veins  in the rock as magma solidified near the surface   it made it worth mining and millions of years  after its formation it sparked the death valley   gold rush it's a wonderful example of a gold mine  shaft it's the eureka mine high up in the panama   mountains associated with trying to find gold  in the granites that were intruded into these   rocks 100 to 200 million years ago the gold  would have been in veins these fingers would   have been injected up into these rocks and the  gold would have been concentrated in these veins   the gold rush here lasted just a few years  miners often had to remove a ton of rock to   recover only one tenth of an ounce of gold  enough to produce just a single wedding ring today all that remains are  empty tunnels and ghost towns   it's interesting to consider that the frenzy of  activity mining gold was actually a direct result   of the kind of volcanic activity  100 to 200 million years ago   geologists investigating the battle  that raged in death valley between   fiery volcanoes and ancient seas  have found important evidence stromatolite fossils are proof that death valley  was once submerged by the waters of a shallow   sea veins of granite could only have formed  in the fiery heat of the volcanoes that burst   to the surface around 100 million  years ago and drove that sea away   the volcanoes built up the land that was to  become death valley into peaks as high as   the cascades mountain range but deep beneath  the earth's surface awesome geological forces   were about to destroy those peaks stretch the land  apart and transform the mountains of death valley   into the lowest point in the u.s a billion years  death valley remained a flat plain under the sea around 100 million years ago erupting  volcanoes formed high mountain ranges   but then the real geological mystery began the  land here must have undergone an extraordinary   transformation because today in death valley those  high mountain ranges have vanished incredibly the   one-time mountains have sunk below sea level  to become the lowest point in north america yet all around the valley snow-capped peaks  still soar up to 11 000 feet into the air the investigation digs deep under the landscape  to discover what vast geological forces could have   caused that huge difference in height between  two places just 20 miles away from each other   there are a lot of mysterious aspects about death  valley it's a unique landscape because the valley   floor itself is is very deep it's below sea  level and the mountains rise up very steeply on   either side clues to the power  of these underground forces   lie all over the valley if you know where to  look many of the rock layers were originally   deposited on the ancient flat seabed they  can still be seen as horizontal layers   but other nearby layers aren't horizontal  at all they tilt downwards into the ground miller finds a further clue of earth's power  in the unusual shape of this cinder cone   a mound of ash and debris lying on death  valley's floor it looks like it's two   cinder cones but in fact it's really just one  that's been pulled apart along a big fault zone   this has moved some 700 feet in some 700 000 years  so that's about a foot per thousand years which   sounds like it's really really slow but if you  look at it over a great length of geologic time   you get quite a lot of slip and give it  even longer time it'll be offset even more   miller's next challenge is explaining what is  making the fault line move for that she studies   other ancient rock formations whose jagged  outline has given them the name turtlebacks   the turtlebacks are crucial to understanding death  valley's early origins they have so much of the   record here if you're willing to  spend time to try to unravel it the real clue lies in the  rock's distinctive texture   if you just take a look at this rock closely you  can see that it's very kind of strung out very   stringy it tends to be a pretty fine grained this  texture tells miller where these rocks came from   we see evidence that these rocks were deformed  just like if you take a piece of plastic and   where to heat it up you could bend it it's the  same thing with rock and so these rocks formed   at high temperatures and pressures within the  earth's crust at depths of about 10 miles or so   and they have since been brought to  the earth's surface concluded that   some overwhelming underground force must have  raised the turtleback rocks to the surface   and stretched them out like warm toffee as  death valley formed the final explanation   of what happened here once again came back  to the way continents drift around the globe as the collision of the plates that had forced  ancient volcanoes to the surface slowed down and   ceased the high mountains that once dominated the  land were slowly pulled apart and tilted downwards gradually as the underlying crust grew thinner  and thinner a deep basin formed between the   mountain ranges death valley is the most extreme  example of what such stretching forces can do   by measuring seismic waves scientists discovered  that here the continental crust is just 16 miles   thick this might sound like a lot but it is far  thinner than almost anywhere else on the planet   around the globe the earth's continental crust  averages 25 miles thick it's strongest beneath   the himalayas at 43 miles thick enough to support  the weight of massive mountains such as everest the turtleback rocks also offer miller evidence  as to when death valley's stretching started dating these rocks reveals that the deformation  started here around 13 million years ago although   death valley did not take on its final shape  immediately death valley is really young   when you look at the whole geologic  time scale modern death valley is   probably three or four million years old at the  most the stretching started before that but death   valley itself is a very recent feature scientists  know that the process is far from finished   they've found irrefutable evidence in the alien  death valley landscape known as bad water basin   i'm standing here at bad water which is the lowest  point in the western hemisphere it's 282 feet   below sea level we're actually standing below  sea level about the depth of a football field this floor has been sinking it's about  a tenth of an inch per year which is   about half of the speed at which your fingernail  grows continual stretching of the earth's   crust has turned bad water into one of the  lowest spots on any continent on the planet   yet its true depth is even lower still the surface  that we see here is the present-day surface   but what one has to realize is that beneath  our feet we can go down through sediment that   represents ancient periods of time when death  valley was a surface that goes down three miles   you would need to drill down  through the sediment to a depth   equivalent to 11 empire state buildings end  to end before you hit the crustal bedrock the total volume of material in this basin would  bury new york to the depth of nearly a mile the valley floor is constantly being covered with  sediment cascading from the surrounding mountains   but it can never fill up completely the sediment  is coming in at a rate that is less than   the rate of sinking of death valley itself  so that we're always maintaining a surface   here on the valley that is sitting below  sea level and is continuing to sink   through time this constant movement shows  earth's geological forces at their most dynamic   and makes death valley unique the allure is that  nowhere on earth do we see continental crust   being pulled apart at this rate or this  magnitude the investigation into death   valley's creation has established how it sank  to become the lowest point in north america the turtleback rocks were deformed  by the powerful tectonic forces   pulling the mountains apart  to form a wide valley floor the still sinking landscape of bad  water currently 282 feet below sea level   is proof that the crust here  is still being stretched today   but the sinking of death valley is just one  part of the story geologists still need to   investigate how one of the hottest places on  earth was shaped by the power of moving ice 1.2 billion years ago death valley  was submerged by ancient seas   around a billion years later volcanic  mountains drove the seas away thirteen million years ago the continental  crust started stretching apart here   and by three million years ago death valley  was one of the lowest points on earth the clue that showed investigators  what happened next was the discovery   in the valley of a little-known but  highly valued white crystalline rock when one thinks of prospectors in the death valley  region one often thinks of them hunting for gold   and for silver but there was one mineral that was  much less glamorous much less sexy and exciting   and that was borax but it was actually known as  the white gold of the desert in 1880 borax was   a rare but in demand mineral used in antiseptics  and detergents one impoverished couple desperately   trying to make a living in death valley was  aaron and rosie winters they heard from a   passing prospector that they could make good money  from borax if they could find it they learned from   their fellow prospector the then secret method of  testing rock for borax anxious to keep potential   profits for themselves the couple waited until the  dead of night to perform the test in death valley   you burn the mineral to see if the powder that  we have in front of us here contains any borax   now what the winters did is to add sulfuric acid  to borax bearing mineral we'll add some alcohol   the winters probably used cheap whiskey back  in 1880 and the flame should burn hopefully a   green color if borax is there and as we can  see the flame is green in color and in 1880   the winters knew that they would become  wealthy because they had borax from these   humble beginnings a whole industry grew in death  valley it made the winter's fortune and also gave   scientists a priceless clue in their quest to  understand the geological history of death valley because borax deposits like these can only be  found in the beds of ancient freshwater lakes   the sea water that once covered this valley  had long gone a billion or more years earlier   but the presence of borax proves that fresh  water must have flooded into the area when ice   age glaciers started to melt from the surrounding  mountains around two hundred thousand years ago   as the glaciers melted rivers  flowed towards the lowest point   death valley gradually a vast lake spread  out across the flooded valley floor the valley's catchment area was huge its rivers  drained more than nine thousand square miles   an area bigger than new hampshire the water  pouring in from the surrounding mountains   leeched minerals such as borax from the  rocks and deposited them on the lake bed in a lot of the lake beds this mineral borax would  appear as a kind of a white fuzzy mineral it's   actually called cotton ball the borax proved  that a lake existed here geologists called it   lake manley after one of the pioneers william  l manley who had named death valley in 1849 but they had no evidence to  tell them its depth and its size a solution to this puzzle is  revealed in this small hill   with a road cut straight through it near the  valley's edge at a spot called beady junction   it's very fortunate to have a road cut right  through this gravel deposit so in the exposure   we can see very well rounded pebbles we  can also see some crude layering in the   gravels and they're stacked in against  each other and we call that shingling   the shape and the smoothness of the stones  tells caskey exactly how these pebbles got here   the way their stack tells us that the direction of  water flow that laid these pebbles down like this   was from the right to the left so we know that  this had to be wave action that strong evidence   that this is a beach environment by looking at the  height of this pebble beach above the valley floor   caskey calculates the dimensions of the lake from  this speech gravel bar that we're standing on   the waves would have been crashing at our feet  and as we look south it's hard to imagine a   lake sitting out there across that vast salt  pan but lake manly would have covered about   600 square miles and it would have been about  450 feet deep it's odd mapping shorelines on   a really hot day in death valley you kind  of long for the the ancient days of yore   when there were big lakes out here you imagine  this was a beautiful place full of lush vegetation   yeah it was quite a different place than it is  today for caskey the next step is discovering why   death valley no longer has a lake and there is  evidence about that in one of its most unusual   landscapes this twisted jagged field of white  peaks that's called the devil's golf course even the sounds here are mysterious in  the silence of the desert there is a faint   popping noise as the relentless sun sucks every  drop of moisture out of the parched surface   the salt that we see here is the remains  of an ancient lake it's called devil's golf   course because it's probably the least likely  surface that you would ever want to play golf on the surface is made up of rough salt crystals  popping when they expand and contract in the   searing heat but this salt did not come from  the sea just like the borax the salt was leached   from the rocks when fresh water started flowing  into death valley two hundred thousand years ago   the salt was originally dissolved  in the freshwater lake manly   and caskey has a simple experiment to show exactly  how it ended up on the floor of death valley   i'll pour the water and salt solution  into this pan and as the water evaporates   we should see salt forming and that's  exactly how this salt crust forms it's hot enough out here today it  should evaporate pretty quickly   in fairly short amount of time some beautiful  salt crystals formed along the edges   but that's essentially how salt pan  forms when the rain water comes in   the salt goes into solution uh basically just  like the water that we have in this water bottle   and from the moment the water starts  evaporating salt crystals start forming today death valley salt pans  cover more than 200 square miles   an area three times the size of washington  dc they are the remnants of the ancient lake   that finally disappeared two thousand years  ago when earth's climate began to warm up   from then onwards death valley's  temperatures just kept on rising   death valley is definitely one of the  hottest spots in the world the record high   was 134 degrees fahrenheit recorded back in july  10th 1913 and just to give you perspective on   that the caretaker of the furnace creek ranch  who actually was the one doing the recordings   back then he describes that day as being so  hot he saw the swallows falling dead in flight geologists today understand how  death valley's unusual geology   is responsible for the punishing  climate that killed off its lake   it stays so dry because there are three  distinct mountain ranges between death valley   and the moisture carried off of the pacific ocean  over 200 miles away we have the sierra nevada to   the west of us the storms come in from the west  laden with moisture as they rise up they lose   most of that moisture on the west side and each  set of mountains wicks a little more moisture   out of the clouds and here with our three sets  of mountains in between us and the ocean by the   time that moisture to get to death valley there's  either all gone or we just get a few drops of rain almost all storms from the coast are stopped by  the three mountain ranges each one in turn having   an effect the scientists call a rain shadow so we  are in the rain shadow of a rain shadow of a rain   shadow an average less than two inches a year and  there is another way that geology influences the   desert climate air heated under the cloudless  sky is trapped by the surrounding mountains   in summer death valley becomes  a deadly dangerous furnace   the local weather station provides a graphic  demonstration of how quickly that heat could have   destroyed death valley's lake every day caligan  checks the rate of evaporation the summer months   it may take five of these containers  here so i'm going to fill them up   and dump them into the pond until it  brings the water level up to the needle   now our average rainfall is barely two inches  a year but the evaporation pond records up to   150 inches of evaporation that huge discrepancy  between the amount of rainfall and the speed of   evaporation means that a lake 12 feet deep and 30  miles long would evaporate in just a single year   lake manley was bigger than that but  over time it never stood a chance the scientists studies of death valley have  solved the mysteries of its freshwater past borax   discovered here in the 1880s proves that death  valley was once filled with a freshwater lake   pebbles unearthed on an ancient shoreline  show the lake once covered 600 square miles   an area three times the size of chicago when the  last fresh water pools dried up here two thousand   years ago death valley started its reign as the  driest place in the u.s which makes it ironic   that the investigation's next phase examining  the valley's most recent geological upheavals   involves scientists studying the  awesome power of fast flowing water around 100 million years ago death valley's  ancient seas gave way to exploding volcanoes   whose peaks were then wrenched  apart to create the lowest spot   in america from around 200 000 years ago  the valley filled with a freshwater lake   but the rain shadow of surrounding  mountains dried up the water for the past 2000 years  death valley has been hotter   and drier than anywhere else in north america which makes it all the more  mysterious to find mosaic canyon   a deep chasm seemingly cut by  water in this parched and arid land especially when there is evidence of massive  boulders having been pushed around like pebbles just look at the size of that boulder and look at  how high above my feet it is it's about three feet   in diameter and i can't even estimate what  the weight of that thing is she may be in a   desert but messina knows there is only one force  that could have lifted the boulder up so high   water brought it here and left it here the force  of the water that came through here had to have   been pretty severe in order to get that boulder  up there plastered against the wall this boulder   gives us evidence about the force of the water  that comes down these canyons during flash floods a flash flood is one of  nature's most lethal weapons   if there were a flash flood coming down this  canyon i wouldn't have enough time to run out   of its path because the water flows down at an  incredible velocity flash floods are among the   most violent processes on the earth they can carry  material the size of an suv without any problem   at all in one of the driest places in the world  the flood water comes from a surprising source rain on average death valley receives  just two inches of rain a year this is less than half the rain that  falls on new york in a single month   but violent summer storms mean it  can all fall in just a single day the floods transform the desert landscape in a  number of ways one is known as the desert bloom   where seeds and plants that may  have lain dormant for up to 10 years   burst into flower after a sudden  rainfall this phenomenon might be   beautiful but there is another deadlier  side to these floods with a human cost   in 2004 there was a flash flood that came down  furnace creek it was just this muddy slurry that   was dense enough to pick up a vehicle and carry  it downhill and several people died in it the   2004 flash flood is small in comparison to some of  the events that we see preserved here in the rocks   flash floods happen all over the world but  there's evidence here of their particular and rare   geological effect in death valley this marble  is very highly polished it's not scratched   it's not gouged it's been polished by very  fine grain material it comes down as part of   a flash flood so it's really smooth  and it's fluted it's really unique to uncover how these unusual polished walls  were formed messina takes a closer look at   what geologists term the badlands i think it's  called bad because nothing will grow on it   there's just this very loose material out here  and it erodes so readily that plants can't even   take root so this is bad land the rock that  makes up the badlands is the dried-up remains   of the two thousand-year-old lake bed that once  submerged death valley this is nothing more than   desiccated mud it's called mudstone because it's  slightly lithified meaning it's turned into rock the mudstone's minerals are arranged in tightly  packed flat sheets the rain can't penetrate the   mudstone and therefore the rain picks up a  lot of particles and carries them downhill   these particles are the key to  the canyon's smooth polished walls it flows through here so laden with  sediment that it causes a lot of polishing   and incision so every time  a flash flood comes through   this canyon gets deeper the walls get  higher and the rock gets more polished the sediment-laden floods can carve into death  valley's rocks with tremendous speed and force   these canyons have been gouged out where the rocks   here have been fractured and weakened by the  continuous stretching the valley is undergoing this is up front in your face geology happening  right here death valley is dynamic this is a   place where things are happening in a human  lifespan in this arid desert the investigation   has identified water as the latest factor in  death valley's continuing geological evolution   the giant boulders plastered high  on the canyon walls illustrate the   power of flash flooding in the desert the  smooth walls of mosaic canyon show how the   dried mud from an ancient lake still affects  how death valley is being shaped to this day and yet some mysteries remain unsolved   including one of the world's most  intriguing geological riddles   the rocks that seem to walk by themselves moving  thousands of feet across the floor of death valley over 1.2 billion years death valley  has been transformed from a watery   landscape to a barren desert even though  geologists now understand the processes   that have shaped this extraordinary region  there are still mysteries to be solved   and there is no part of death valley more  mysterious than an area known as the race track this parched cracked lake basin just two and a  half miles long and a mile wide is the setting   for one of death valley's most intriguing  geological puzzles it's sliding stones i love this place because it's odd  i could come here 100 more times and   every time there'll be something  different something i didn't see   stretching behind these rocks are  long grooved trails in the earth   it is clear that they are tracks left behind  as the rocks move across the valley floor   the puzzle is to work out how the rocks can  slide uphill against this slightly tilted surface   these are no mere pebbles some of these rocks  are over 700 pounds and some of the trails are   nearly 3 000 feet long the phenomenon  was first recorded here by scientists   some 100 years ago and yet in this remote  location no one has ever seen the rocks moving messina has been tracking the movement of each  individual rock on the racetrack since 1996.   her gps readings are accurate to within a  single inch geology is really nothing more than   detective work and rather than looking for  evidence of things that took place a long time ago   what i really like about working on the racetrack  is you're looking at things that are happening   right now it's an ongoing process her first  clue is the surface on which the rocks slide   if i try to move my hand over it i could probably  file my nails right now however after it rains   there's so much clay in the lake bed sediments  that it gets slick it's almost like teflon you   wouldn't need very much force to set even a  very large rock into motion just because the   friction on the surface is almost nil but water  alone isn't enough to make these rocks move messina has identified a second factor at work you  can have rain but if you don't have wind a couple   of days later i don't think these rocks are going  anywhere the racetrack is a natural wind tunnel the wind funnels into the valley from the south   close to the ground the winds can exceed hurricane  strength reaching speeds of over 90 miles per hour   enough to push the rocks into action if  you have wind and there is no friction   all you'd need to do is hit a rock with your  finger like that and it would go into motion   when all these elements are in place the  rocks can begin their mysterious journey since no one has ever seen the rocks in motion we  can only guess how fast they go but based on some   of the evidence that i've seen these rocks aren't  inching along by any means and the best estimate   we have is about three to four miles an hour so  a nice brisk walk but until this phenomenon is   witnessed the mystery of death valley's sliding  rocks will remain i hope that this mystery   isn't solved it's what keeps me interested and i  think it's what keeps a lot of people interested geologists studying death valley have figured  out its extraordinary geological evolution stromatolite fossils show that  this area was once covered by   seas turtleback rocks proved that the land  was stretched apart by tectonic forces   dropping the valley floor down  to the lowest point in america   pebbles at bd junction proved that death  valley was once covered with a freshwater lake   and the smooth polished walls of mosaic canyon  show that water is still at the heart of death   valley's modern evolution death valley remains one  of the most extreme geological wonders on earth   and it's still evolving its valley floor is being  constantly pushed apart by forces deep within the   earth this means that the crust here will continue  to stretch and thin one day tens of millions of   years into the future death valley could be  separated by the sea from the rest of the u.s today death valley continues to sink at a  steady rate of one-tenth of an inch a year   while its surface continues to be sculpted by  water living proof that the earth is never at rest

Channel: HISTORY

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Id: df_wlhfrIrI

Length: 44min 22sec (2662 seconds)

Published: Sat Feb 27 2021