Why Did The Earth Totally Freeze For 100 Million Years?

light flickers on the low ceiling a horn is visible or is it a tusk antlers huge antlers diverge and reach across the narrow cave a vast herd of animals comes into view deer horses bison and amongst them stranger creatures beasts long dead in this part of the world orocks stretch along the walls whilst giant deer are stalked by prides of cave lions the prehistoric people of lasso in modern day france had come to these caves for generations layering images of fear and wonder on top of one another like graffiti whose meaning and significance only they could say these elaborate caves contain no dates no indication of when they were created yet the modern day absence of aurochs giant deer and cave lions hints at a great age a time when these exotic animals roamed the valleys around lasso today carbon dating has revealed that these talented artists lived around 17 000 years ago during the upper paleolithic a time of great struggle for much of the world was in the grip of an ice age the likes of which humanity had never seen before things had been cold on earth with ice caps at the poles and chilly northern winters for most of human history but about 26 and a half thousand years ago it took a turn for the worse average temperatures plummeted to around 6 degrees celsius colder than today and ice sheets grew and extended down from the arctic circle to the middle of europe and the north american continent around a quarter of the world's land surface was totally covered in ice and sea level dropped 125 meters lower than it is now this period known to scientists as the last glacial maximum saw the northern hemisphere transformed making survival tough for the paleolithic humans who called it home these glacial conditions created cold and dry weather with strong winds blowing dust into the atmosphere but little rainfall to rain it back out deep red sunsets would be reflected from the icy permafrost and tundra that spread across europe as fur-clad bands of early humans roamed back and forth across the edge of the ice sheet stalking long extinct monsters life in the ice age was hard but lasso was a refuge for these people a sheltered spot to regroup and reflect on their hunting victories and losses of course many other bands of humans may have retreated south where temperatures were warmer and the ice was a distant memory we don't know if the lasso tribes survived through the last glacial maximum but certainly the human race clung on in the refuges away from the ice this was because once the last ice age was certainly intense it wasn't global there were plenty of places on earth that weren't frozen the grip of this 5 000 year winter may have been hard for humanity but there is evidence for much harder times in earth's history times when there would have been no escape from the ice at all when it wasn't even certain if the earth would be able to break free for just over half a billion years before the lasso made their home a spectacular event may have struck our world an event known informally by climate scientists today a snowball earth but did these total global glaciations really happen how could such extreme ice ages even occur and what would they have meant for earth and its precious precarious life [Music] the cave of the hundred mammoths is a fascinating cave system in france covered with engravings and drawings of ancient mammoths they ruled the earth at the same time as the lasso peoples not only in france but all over the world and so our documentary recommendation on curiosity stream this month is ancient yellowstone mammoth country a fascinating dive into the fertile hunting grounds for paleontologists atop the ancient supervolcano ancient yellowstone is a great series in general and just the tip of the iceberg when it comes to the thousands of documentaries available on curiosity stream on topics ranging from ancient history to deep space curiosity stream is also a bargain at less than 20 dollars a year and has fantastic new shows popping up every week so go to curiositystream.com forward slash history of the earth to sign up and using the promo code history of the earth will save you 25 percent bringing a full year down to 14.99 just over a dollar a month thanks to curiositystream for supporting education on youtube [Music] douglas mauson trudges on and on through the snow flurries and blistering antarctic wind sliding one foot in front of the other his skis slice through the fresh snow and his poles impale the drifts he barely feels the weight of the sled behind him anymore after three years in the field it is as much a part of his body as his own arms or legs but now on the last stretch of his final journey mawson is numb inside and out two months earlier in november 1912 the australian geologist had set out with two other explorers xavier mertz and belgrave ninis to map the coastline of the australian portion of antarctica the expedition had gone well for the first five weeks with the three men and a raft of sled dogs speeding across the white featureless expanse a disaster had struck when ninis's sled fell through the snow covering a crevasse and he his dogs on more than half of the party's supplies disappeared into the heart of the glacier ninis was never found and mawson and mertz turned back immediately with so few provisions for themselves and the remaining huskies the pair were forced to eat their own dogs exhausted sick broken in mind and spirit but with still more than 100 miles to go before base camp mertz took a turn for the worse he became delirious biting off the tip of his own finger raging violently and suffering seizures before falling into a coma and dying it later transpired that he had been poisoned by vitamin a from the sled dog's livers mawson was alone but had no choice to continue or face death himself he eventually made the lonely journey back to his camp but his bad luck followed him back he finally arrived to discover that the ship due to take him home had already left just a few hours earlier forcing him to spend another winter on the ice with more than enough time to mourn his lost companions despite these horrors upon returning home mawson was awarded with a knighthood and his venture had uncovered such a wealth of biological and geological data that it took 30 years to fully unfold though he did later return to antarctica mawson spent much of the rest of his career studying the geology of his native australia as professor of geology at the university of adelaide he had ample opportunity to consider the geological history of the entire country and there was perhaps no one more suited to interpret the mysterious rocks that researchers and prospectors were discovering across a swathe of the sun-baked continent there appeared to be almost 1 000 miles of galacial sediments they were clearly out of place but they were also incredibly ancient dating back to the neoproterozoic period long before the evolution of animals mawson doubtless drew on both his geological and antarctic experience when he made a remarkable suggestion perhaps he said the whole of australia had once been entombed in ice in some kind of global glaciation how else could you explain the freezing of a place as hot as australia if not by the freezing of the entire world mawson's geological and glaciological reasoning were sound but they failed to account for one thing continental drift as the theories of continental drift and subsequently plate tectonics gained ground they helped geologists to solve the puzzle of these seemingly incongruous deposits accepting that the continental masses travelled across the face of the earth as crustal plates scraped collided were destroyed and made anew permitted places like australia to become glaciated without the need for a worldwide freeze during the neoproterozoic it turned out australia simply lay closer to the poles and was therefore more likely to experience normal polar conditions plate tectonics may have undermined mawson's conclusions but that wasn't the end for his ideas as geologists learned to reconstruct the shuffling of continents through geological time new sedimentary conundrums began to present themselves for one galacial deposits have been found in greenland and on the arctic island of svalbard on the surface this is perhaps not surprising since both of these places experience long polar nights and year-round freezing conditions but these particular deposits date from around 650 million years ago when tectonic reconstructions suggest that svalbard and greenland lay at tropical latitudes ancient ice in australia may not indicate a global glacier but ancient ice on greenland does but it's not just these two places that hint at an extraordinary neoproterozoic glaciation all over the world geologists use elemental isotopes and local relationships to find the age of their rocks and they use the alignment of ferromagnetic minerals like hematite and magnetite to the earth's magnetic field to find the latitudes at which these rocks were formed finally they use clues in the rocks themselves to reconstruct the paleo environment and by extension the paleo climate at that particular location researchers began to find characteristically glacial deposits from the late neoproterozoic worldwide they include chaotic unsorted sediments known as tillites which are created by the action of glaciers as they churn up existing rock and deposit it there are also drop stones large cobbles or pebbles that appear to have been dropped from above into much finer layered sediment without having to invoke mysterious rock-slinging deities these anomalies can be explained by melting icebergs dropping their sediment load far out to sea passing glaciers can also polish rock surfaces and leave long straight scratches known as striations and lakes that form from glacial melt water record accumulate finely layered sediments at their bottoms called valves which reveal the seasonal ebb and flow of melting waters all of these features have been found in rocks from the late neoproterozoic and most importantly regardless of the latitude in which they were formed drop stones valves and tilites from near the equator lead to the inescapable conclusion that there was ice here and the planet must have looked very different to today not only that but late neoproterozoic deposits contain some rare and unique rock types that are hard to explain without drastic climatic and oceanographic transformation banded iron formations which disappeared from the planet some one and a half billion years earlier now make their reappearance in rocks from 700 million years ago their presence implies oceans that were occasionally anoxic something that would only be possible in the neoproterozoic waters if something was stopping gases from being exchanged between the atmosphere and ocean something perhaps like an immense uninterrupted ice sheet that covered the global ocean like a shell finally in a stroke of remarkable geological synchronicity researchers have consistently found a single type of rock laid down worldwide directly above the widespread glacial deposits no one is sure exactly how or why the cab carbonates formed all around the world all at the same time but a leading explanation involves the sudden influx of new material from the land surface into an ocean that had become strongly acidic with carbonic acid alternatively the cab carbonates may just represent the moment the oceans breathed again after a long and constricting global freeze [Music] and so all of these pieces of geological evidence seemed to point to the same remarkable conclusion in the late neoproterozoic starting around 750 million years ago the earth experienced an intense ice age that saw widespread freezing of the land and ocean a global glaciation that caused ice to extend from the poles right down to the tropics perhaps even meeting at the equator an ice house world that transformed the earth from a watery paradise to a barren almost lifeless ball of ice and what's more this probably didn't happen once but up to four times in quick succession right up until the dawn of animal life american geologist joseph kirschvink aptly named these global glaciations snowball earths for the way they turned our diverse blue marble into nothing more than a featureless white orb but the period of geological time in which many of these extreme events occur is known as the cryogenian after the greek for frost now that neoproterozoic rocks have been studied in detail the individual glaciations are named after the rock formations where they were first identified the stereo glaciation is the oldest occurring between 750 and 660 million years ago it's followed shortly after by the marinoan ice age from 650 to 635 million years ago records suggest that a very brief global glaciation followed 579 million years ago and the final snowball earth is known as the bakernurian glaciation and it marks the very end of the proterozoic period lasting from 549 to 530 million years ago [Music] it's worth noting that these are not the first times that the planet has been plunged into icy purgatory around two and a half billion years ago the earth was put into a 300 million year long deep freeze as a result of the great oxygenation event and the atmospheric changes that followed but more than fifteen hundred million years have passed since then and the neoproterozoic earth is a very different world life has become complex cooperative and the stakes are higher than ever just how hard will it be to survive on a cryogenian earth [Music] icy comet speeds through the solar system on a slingshot course towards the sun flung on this fateful trajectory millions of years before from its home in the distant kuiper belt it has swung and looped around its star nearly a million times but the lonely comet's days are numbered this may well be its last stellar tour with every approach the sun's heat evaporates some of its icy mantle sending it streaming behind in a glorious rainbow-lit tail and the once magnificent icy asteroid is now but a shadow of its former self nevertheless on it flies it sails past neptune and uranus cold ice giants lurking in the dark onwards and inwards to saturn girdled by rings and looming jupiter with its unruly moons as it pierces through the relative clutter of the rocky asteroid belt the sun's warmth begins to grow and the comet begins to glow on it goes into the inner solar system and past the already dry and dusty mars it's still 700 million years before humanity will evolve to recognize its reddish glow in the night sky but mars has already lost its life-giving atmosphere and oceans to the unforgiving solar wind only a little water remains frozen at the red planet's poles closer still to the sun and the melting comet's days are numbered the earth's single gigantic moon is its penultimate flyby and as the earth itself grows larger in the comet's sights and the sun's heat eats away at the comet's core two frozen bodies glow as brightly as one another on one side of the sky an icy asteroid is about to meet its end and on the earth an entire icy planet there is no end in sight it sits squarely in the warmth of the sun's habitable zone and yet not a drop of liquid water is to be seen in the clear night skies above this snowball earth the comet disintegrates and evaporates into a superheated vapor but on the planet's surface the big freeze continues on a crushing global winter with no easy way out from the air the blindingly sunlit dayside is cast into sharp relief by its shadowed night separated by a smooth terminus uninterrupted by either mountain or valley but the planet's night side is not completely dark the bright white surface reflects the star and moonlight giving an entire hemisphere an eerie grey glow yet it's almost impossible to see the planet spin as the featureless globe slides beneath its shadows time on earth during the cryogenian is just as undifferentiated as its geography seasons pass winter to summer but with no visible change on the surface all remains white years decades and millennia pass through cycles of solar activity and subtle changes in earth's orbit and spin but still there is no visible change on the surface it's easy to lose track of time and before you know it 90 million years have passed it is only when on the surface that it's possible to differentiate between icy land and icy ocean the sea ice appears as an endless smooth expanse interrupted only by larger icebergs trapped and frozen in place but approaching the hidden shoreline the ice cracks and heaves in chaotic slow motion the result of tidal forces bulging the still liquid ocean beneath many meters of ice there are long flat white coastal plains that then rise to a rolling rocky landscape but all is smoothed and softened by the indiscriminating blanket of snow and ice only occasionally is a sharp rocky ridge or peak visible blown free of snow and ice by the unforgiving wind indeed wind is likely the only weather that this frozen ball will experience with temperatures at the equator as low as those on modern-day antarctica there's no spare energy in the atmosphere for brewing storms or rain clouds ice covers every surface becoming a barrier to evaporation and making it extremely difficult to pump water vapor into the air without clouds through the night there's little retention of heat close to the surface and at night especially the temperatures plummet even further it is unfathomably dry and cold but still the wind blows from warmer dayside to colder nightside or from extremely cold mountain tops to only very cold shorelines the wind blows uninterrupted across the featureless surface it whips loose snow and ice crystals into a sparkling ice mist and rivers of powder blue across the ground it would be quite beautiful if it weren't so deadly for the surface is most certainly inhospitable to life atop the snow and ice there is none of the water that every life form needs to survive and since snow and ice cover the entire globe there would seem to be nowhere left for earth's fragile inhabitants to cling on and yet cling on they do the ever innovative biological metabolism is capable of endless variations by 750 million years ago bacteria algae and the unicellular ancestors of animals had already adapted to inhabit almost every corner of the oceans and inland waters and were beginning to creep their way onto land from the shores too so when the earth froze over life may have lost most of its territory but it was able to persist in whatever stronghold whatever refugia it might find while on the grand global scale the earth is featurelessly frozen there will always be some fine scale variation some tiny cracks in the facade that life can exploit beneath the thick oceanic ice shelf the oceans are not frozen to the bottom they might be pitch black they might be anoxic and stagnant but there are microbes that can still eke out in existence on such meager rations life's ancestral refuge still exists at the very bottom of these stagnant oceans too hydrothermal vents pump warm mineral-rich water out onto the sea floor and they are colonized by chemilitho autotrophs able to get all they need from the minerals that build the underwater volcanic chimneys there are opportunities for the photosynthesizers too even though the freezing temperatures at the sunlit surface are at first grossly incompatible with these organisms need for light but again cracks in the facade leave space for algae to scrape by where the sea ice has heaved and cracked and changed its shape a million times pockets of water could become trapped close enough to the surface to receive a faint life-giving glimmer similarly as the days and seasons come and go some ice inevitably thins and cracks when exposed to the unforgiving glare of the midday or mid-summer sun producing small areas of translucency or even open water it would freeze again when the sun sets or winter rolls around but life has taken its chance and can sleep out the coldest times in sun-fattened dormancy microbial life is even able to build its own habitable microcosm on the surface of the ice creating and expanding dark water-filled pits that riddled the ice surface like swiss cheese known as kryokanites these vertical holes begin to form when the sunlight seizes up the dark color of dust grains trapped within the ice warming it up more than its surroundings which allows it to melt the ice around it as the hole expands it captures more of the warming dust and it's colonized by dark coloured snow algae that accelerates the warming and melting effect indeed even when the world is at its coldest these cryoconites are proof that life not only finds a way but helps to engineer its own way too and so as remarkable as it may seem even as earth plunged into an apparently eternal ice age it was not accompanied by a mass extinction of life there's no evidence of any great dying or of the loss of any major branch of the tree of life unlike the last deep freeze more than one and a half billion years earlier where scientists believe up to 99 of all living things on the planet perished organisms seem to have muddled through unscathed a remarkable demonstration of what 1.5 billion years of evolution and diversification can do for life's resilience in the face of seemingly impossible odds [Music] planet earth today is in the midst of a climate crisis since the industrial revolution we have been pumping carbon dioxide and greenhouse gases into the atmosphere at a remarkable rate this revolution transformed how we live work and play and fossil fuels and now as invisibly essential to our lives as water is to fish but the carbon they release doesn't belong in our atmosphere it was locked away hundreds of millions of years ago as part of a natural cycle playing out on geological time scales we have broken the wheel for our own immediate gain and are now suffering the consequences overwhelming scientific evidence now points to a single conclusion that human activity is causing the earth to warm at its fastest rate for tens of millions of years while this in itself is bad news things get much worse when we consider the effects of this unprecedented anthropogenic warming as the planet warms it gets harder for ice to remain covering the poles every year during the arctic summer the sea ice retreats further than it did before and soon we might expect the watery north pole to be completely exposed but changes aren't just happening at sea [Music] the land surfaces in the arctic are also frozen as permafrost down many hundreds of meters in places ice turns soft soil into sediment as hard as concrete impenetrable to water and air much of northern canada northern europe and siberia are gripped by a year-round permafrost that stunts and stifles any organism that would choose to live here but global warming is eating away at this permafrost too all over the northern hemisphere the thickness of this frozen layer is diminishing thawing and in the process relinquishing an unexpectedly damaging cargo methane that was created as dead plants and animals decayed within the permafrost is now able to escape into the atmosphere and methane is 25 times more potent as a heat trapping greenhouse gas than carbon dioxide its release into the air only helps the planet to warm up more causing more melting of the arctic permafrost more release of methane more warming and so on this so-called positive feedback is a vicious escalating spiral that could see the already dire effects of human-induced climate change suddenly become catastrophically worse the arctic alone is thought to contain 1500 billion tons of carbon which is almost twice the amount of greenhouse gases already in the atmosphere for context human activity over the last 250 years has increased the amount of these gases by just 50 percent but the positive feedback loop in the arctic could see it jump by 200 percent in mere decades scientists suspect that we have already passed the tipping point for this climatic death spiral and the best we can do now is figure out how to weather the storm sixty years ago in the 1960s humanity was as yet blissfully unaware of the coming climatic apocalypse with the development of modern meteorological methods scientists were just beginning to understand the interconnections of weather and climate across the globe and resembling some of the first climatic models that predicted long-term trends in environmental conditions worldwide during this meteorological renaissance a soviet climate scientist named mikhail budiko perhaps inspired by the brutal winters that assailed his home city of leningrad began considering the effects of different degrees of ice cover on the global climate as anyone who's considered dressing in a hot country with a test light coloured materials reflect the sun's radiation more effectively than dark coloured ones the dark fathomless depths of the ocean soak up 94 percent of what the sun dishes out whereas the same ocean covered by ice will reflect up to 70 percent of that radiation this so-called albedo effect means that cold ice-covered areas tend to stay cold because they bounce back the one thing that can warm them up it is the beginning of a positive feedback loop and buddhico's model assembled the mathematics to discover how far that spiraling rabbit hole went his models showed that if temperatures on earth dropped enough to allow ice cover to reach latitudes of around 25 to 30 degrees north and south level with texas egypt and south africa then the cooling albedo effect would outweigh the warmth from the remaining ocean forcing ice to advance all the way to the equator and so external temperature drivers don't have to be as extreme as one might imagine and the earth's own escalating feedback would take it the rest of the way puriko's reasoning and mathematics was sound but he was quick to doubt his own work the model suggested that once ice reached the equator then the completely ice-covered globe would reach a new thermal equilibrium and losing any mechanism by which it might warm up again essentially if ice ever reached a latitude of 30 degrees then his work suggested the earth would be plunged into an inescapable global ice age from which there could be no thermodynamic reprieve as a result he squarely dismissed the idea that this had ever happened in earth's history for if it had we would still be living on snowball earth nevertheless there is strong geological evidence for tropical glacial deposits during the neoproterozoic and with positive feedback in the loop we can reasonably expect that to mean ice extended all the way to the equator but budico's model does offer a little help to scientists as they search for reasons for the global snowball we only need to find mechanisms that can create a tropical ice age rather than an equatorial one although average global temperatures for much of the cryogenian would have hovered around -50 degrees celsius we are only looking for a mechanism that can drive average temperatures down to near freezing point and for that there are a few viable options [Music] the first snowball earth also known as the huronian glaciation around 2.4 billion years ago was likely caused by a sudden and catastrophic change in the earth's atmospheric composition the appearance of organisms capable of making energy by oxygenic photosynthesis saw oxygen begin to replace greenhouse gases in the atmosphere photosynthetic algae consumed carbon dioxide and emitted oxygen which in turn reacted with any methane in the air turning it into the much less potent carbon dioxide which in turn became fuel for more photosynthesis it was this intrinsic change in the earth's heat balance in how much heat the atmosphere was able to trap that saw global temperatures drop and then as a result of positive feedback plummet a similar situation could have occurred during the cryogenian although the mechanism for atmospheric transformation is harder to pin down perhaps a particularly productive time for photosynthetic life saw an uncommonly large amount of carbon dioxide pulled out of the atmosphere or perhaps a particular configuration of land masses was conducive to intense weathering that consumed carbon dioxide through chemical rather than biological means however there is little evidence in the rock record of either biological or chemical drawdown if earth's levels of insulating carbon dioxide suddenly dropped then they did so without leaving a conclusive trace if there is no evidence for intrinsic long-term changes to trigger a snowball earth then perhaps the cause was more acute in the form of a sudden and extreme change in incoming solar radiation modern scientists believe that a relatively short-lived event has the capacity to trigger extreme planetary cooling providing its intense enough perhaps those changes came from outside the earth itself as the sun went through a particularly quiet period with much reduced activity or a combination of orbital changes that seized the planet's tilt and orbital path subtly tweaked to produce intense polar winters alternatively a reduction of solar radiation could have come from within an eruption of an immense super volcano the size of yellowstone or larger would release so much ash and reflective gases into the atmosphere that they would encircle the globe and block solar rays for many years to come the planet would be plunged into a dim nuclear winter and by the time the dust has cleared the positive feedback is well underway one final piece of the puzzle seems to be the distribution of continents across the earth's surface and there is a growing body of evidence that suggests that a large supercontinent close to the equator is a necessity if you are to end up with a frozen snowball earth in general continents are cooler and more reflective than the darkness of the open ocean so they could help to accelerate and exacerbate the cooling process but tropical continents go one step further normally the weathering of land surfaces pulls carbon dioxide out of the air and so tends to reduce the global warmth by nibbling away at the greenhouse effect it is the beginning of a stabilizing negative feedback that keeps conditions within certain narrow bands when global temperatures drop below a certain level the land becomes cold and the rate of weathering here slows down there is less carbon dioxide being removed from the atmosphere allowing the greenhouse effect to bloom and warm the planet once again however when there is land at the tropics this stabilizing negative feedback has less hold over the global climate land that is exposed at tropical latitude is much more likely to continue to be weathered even as global temperatures fall so temperatures are dropping but so are levels of insulating carbon dioxide there is no negative feedback here and the cooling can continue uninterrupted it's a compelling thermodynamic theory except for one important detail for all other serious glaciations through earth's history there has been land at the poles providing a surface on which ice can grow was their land at the poles or at the equator at the beginning of the cryogenian unfortunately conclusive reconstructions are difficult because of a lack of suitable sediment [Music] and so with more and more evidence that it did in fact happen there is one big question that we need to answer it is clear that this was not terminal indeed a few million years after these events the cambrian explosion took place a remarkable unparalleled diversification of life on earth an event clearly impossible on a planet covered with ice from pole to equator we need to find an explanation for how the world recovered just how did the snowball earth end professor joseph kirschvink has made a name for himself as the real life iron man for more than 30 years he has walked the crowded caltech campus contemplating the many things we stand to learn by studying magnetic materials what they can tell us about biology the history of life and the history of the earth itself it was he who first suggested that banded iron formations might come about through a wide scale global glaciation that effectively cut off ocean circulation and in doing so he was the first to coin the term snowball earth and yet unlike michael boudicco who foresaw apocalypse in positive feedback loops kirschvink was not so disturbed by the consequences of such a glaciation climate models could only tell you so much he reasoned and the earth is a complex system that could not be described by simple energy in energy out nevertheless the doomsday scenario predicted by boudicco had seized the imaginations of the public and scientists alike and the theorized finality of a snowball earth has been used to cast doubt on the theory [Music] indeed to this day there is disagreement in the scientific community as to the true extent of the neoproterozoic glaciations in order to make a claim for an extraordinary global ice event there must be extraordinary evidence to support it for one the deposits must be unquestionably glacial they must have definitely formed at low latitudes and no other rock types should have formed at the same time unfortunately 700 million years has been plenty of time for the clarity of that evidence to become obscured rocks that have been interpreted as glacial tills and iceberg drop stones could have formed by other means with no need for ice at all the paleomagnetic evidence that points to tropical latitudes for these rocks relies on the assumption that the earth's magnetic field has always been what it is today had the magnetic poles wandered that our sense of direction on the neoproterozoic earth would be irrevocably skewed and finally it is difficult to sort through the precise chronology of rocks that are found all over the world geologists usually use fossils that date to a very specific period of time but in the neoproterozoic before the appearance of large-scale fossil groups that precision just isn't available and so since none of this evidence is as solid as it could be some researchers have suggested that the neoproterozoic events were no different to other glacial periods in earth's history like the one we are living in right now there is ice at the poles and at high elevations and ice sheets wax and wane through the seasons and millennia but there is no global freeze or alternatively an intermediate situation prevailed instead of a snowball there may have been a slush ball earth which saw ice extend down to subtropical latitudes while the equator remained ice free or with a band of thin seasonal ice this would have allowed some continuation of the hydrological cycle through these periods and would help to explain some of the sedimentary rocks that seem to form in open water or from moving ice indeed it is important to remember here that the earth is never static the movement of tectonic plates across the earth's crust could have periodically cracked the planet's icy shell opening up pools of open water and offering some reprieve from the global freeze however even if ice came to hold our planet in its full grip in a full-blown snowball earth joseph kirschvink still saw a way to escape while the earth is frozen many of its dynamic processes and cycles come to a halt without open ocean the water cycle ceases without life and water the carbon cycle winds down to a mere trickle that there is nothing about the freezing of the surface that stops the churning of the planet's interior tectonic cycling continues as crustal plates are created and destroyed at their margins with accompanying earthquakes vents and volcanoes and so this is where a in the snowball's icy armor appears active volcanoes continue to pump gases including carbon dioxide and methane into the atmosphere ordinarily that carbon would be cycled back down into the earth via the process of weathering as acid rain forming from dissolved carbon dioxide eats away at the rocks or abundant to life forms in the open ocean can draw it down and lock it away in the carbon of their bodies or limestone of their shells but without either of these cycles working efficiently the carbon dioxide stays stuck in the atmosphere and builds up and up over millions of years of volcanic outgassing we are currently witnessing what happens to the earth when there is an excess of carbon dioxide in the atmosphere the gas traps heat and warms the earth via the greenhouse effect and the more gas there is the more effective this process is and so joseph kirschvink saw how a snowball earth would eventually overbalance and collapse thanks to a supercharged ultra greenhouse effect from accumulated volcanic gas in time the earth sets itself right biology itself may have been a passenger through these wild swings in earth's climate but as with the earth's eternal engine the march of evolution never slows or sits still while we can't know for sure how life scraped by through the intense cold and then sudden heating of the planet it's fair to assume that it experienced some intense pressures to adapt and survive in new extreme conditions as such it may well be that the snowball earth periods of the neoproterozoic acted as evolutionary triggers driving innovations that would come to shape the future of life on the earth and the oceans for instance aquatic algae suffered through the global freeze as their shallow water habitats were iced over but if they found a way to survive with a little less water perhaps attaching to and feeding on the solid exposed tidal flats then they would acquire all the adaptations necessary for taking the big future leap to becoming land plants and so the ends of the snowball periods coincide with some major biological revolutions the enigmatic ediacaran organisms the first multicellular and truly macroscopic communities to appear did so less than 10 million years after the end of the gasquier glaciation and the final baikonurian glaciation may have actually contributed to one of the biggest radiations of life in the history of the planet the cambrian explosion of animals the question still remains however as to how much the living component of our planet contributed to causing these glaciations in the first place ice ages may have kick-started evolution but did evolutionary changes trigger the ice ages too certainly the mechanism is there if some adaptation suddenly allowed life to surge forward in its productivity perhaps able to inhabit a new environmental niche or exploit a new more efficient biochemical pathway then it could have led to a tangible reduction in greenhouse gases enough to trigger a snowball earth this is almost certainly how the first global huronian ice age came about and that huronian period eventually saw the blossoming of eukaryotic life forms and the evolution of sex so it's not unreasonable to imagine that the cryogenian freezes could have been influenced by and in turn influential to the evolution of life although the snowball earths may have been some of the most testing times in our planet's history promising unending global winter and the annihilation of earth's most precious cargo these big freezes have never yet followed through on their threats in fact when considered in the context of all geological time they seem almost to be global resets a chance for processes worldwide to stop and restart perhaps beginning on a new course that would come to shape the world as we know it it may be that far from threatening our planet snowball earths have been necessary for creating our modern temperate earth [Music] you've been watching the entire history of the earth don't forget to like and subscribe and leave a comment to tell us what you think i will see you next time [Music]

Channel: History of the Earth

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Length: 49min 11sec (2951 seconds)

Published: Wed Aug 31 2022