When Antarctica Was Green

When Antarctica Was Green

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it's the world's most remote and isolated continent it's home to glaciers mountains plants and penguins but today Antarctica is noteworthy for what it doesn't have in modern Antarctica there aren't any trees or native terrestrial mammals reptiles or amphibians at all but it wasn't always like this thanks to plate tectonics Antarctica has been connected to lots of other continents at various points in deep time as a matter of fact before the start of the Eocene epoch about 56 million years ago Antarctica was still joined to both Australia and South
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America and the fossil record tells us that in the early Eocene antarctica was a warm forested place very different from the continent we know today palm trees thrived there as did flowering plants dung beetles and even a number of hoofed mammals ian's marsupials and because of the way it was situated Antarctica probably served as an important migration path for the ancestors of some of the southern hemisphere's most charismatic mammals like Wallabies and kangaroos eventually of course the lush environment of Eocene Antarctica transitioned into the cold
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glacier covered landmass that it is today isolated from the rest of the world by the most powerful ocean currents on the planet but it turns out that a lot of what we recognize about the southern hemisphere including those famously unique animals of Australia can be traced back to the time when Antarctica was Green [Music] if you could travel back in time and visit Antarctica in the Eocene epoch the first thing you'd notice would probably be the greenery off the coast of Wilkie's land in eastern Antarctica scientists have discovered spora morphs
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fossilized pollen and spores from ancient palm trees and ferns they've also found pollen from other plants that often live in tropical environments today the traces of these warm weather plants can tell us a lot about what Antarctica was like back then since these palms and other trees can't tolerate the cold very well paleontologists think that in the early Eocene the coast of Wilkie's land experienced very mild winters with little to no frost by one estimate the mean annual temperature of that part of Antarctica was around 16 degrees Celsius
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with an average winter temperature of around 11 degrees Celsius so how could ancient Antarctica have been so warm well for one thing the Eocene wasn't the first time that Antarctica's climate was so mild scientists have found spore morphs and other fossils from warm weather plants in Antarctica that date back way to the Devonian period more than 358 million years ago and in the early Jurassic period about 190 million years ago Antarctica was a temperate home for dinosaurs like the long neck Glacia Allosaurus and Cryolophosaurus a
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crested carnivore in those days Antarctica was just one small chunk of the supercontinent Gondwana and it was located a little farther north than it is now but by about a hundred million years ago most of the landmass that would become Antarctica had migrated to the bottom of the world by the early Eocene the western part of Antarctica had just split from the tip of South America but the eastern part was still mostly linked to Australia and right around this time the world was going through a dramatic heat spike this event is known as the paleocene-eocene thermal
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maximum and we did a whole episode about it because the theories about what caused it and what made it stop are really complex and fascinating and a little scary during this period the global average temperature increased by five to eight degrees Celsius in 220,000 years or less and as the world's climate changed so did its flora and fauna tropical trees like palms as well as ferns and tree ferns were able to spread to every continent including Antarctica and mind you Antarctica is a really big
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place like the entire country of Australia can easily fit inside its boundaries so given its size it was able to support many different ecosystems in the Eocene farther inland and at higher elevations spora morphs and leaf impressions have been found from plants that are normally found in temperate rainforests like the southern beech trees it's also been suggested that some areas even experienced monsoons getting more than 60% of their annual rainfall in the summer and of course plants didn't have the whole continent to themselves on seymour island off the
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Antarctic Peninsula paleontologists have recovered brood balls of ancient dung beetles these are balls of dung that female beetles lay their eggs into so if these beetles were rolling dung balls around where did that poop come from well some of it came from ancient marsupials fragmentary remains and isolated teeth tell us that a number of these little mammals lived in Western Antarctica judging by their teeth it seems that some of them belong to the same order of marsupials as the modern colo-colo possum a small and adorable
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insect eater that's native to South America another Antarctic marsupial was an arc todo lops first described in 1984 this possum like critter was the first terrestrial mammal ever discovered in the continents fossil record its ancestors most likely came over from South America other residents of Eocene Antarctica probably came from South America as well for example a single contentious toe bone suggests that zine Arthur ins the group of mammals that includes modern-day sloths might have lived in Antarctica the North rands
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originally evolved in South America as did the forerunners of a herbivore that's been found in Western Antarctica called no TLO fossa the teeth of this creature tell us that it was a browser stripping twigs off a tree branches and maybe eating the occasional sapling not many specimens have been found but we do know there were at least two species of note iolo foes in Antarctica judging by the sizes of their teeth the bigger of these ungulates weighed up to 230 kilograms while its smaller cousin was about 1/4 that size and the fact that these two
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species had such different sizes means that they might have both been specialists eating different types of plants to avoid direct competition with each other another big hoofed mammal known from Eocene deposits in West Antarctica is an arc toad on or Antarctic tooth scientists think that it was a kind of a strap athere an unusual group of extinct and mostly South American herbivores the only Antarctic on fossils that have turned up so far are teeth but more complete skeletons of other a strap athere's show that these animals looked
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kind of like tapers some species had self sharpening canine teeth and eat a combination of soft plants and hard nuts others may have been semi aquatic like modern-day hippos and paleontologists think an arc de don was yet another animal whose ancestors crossed into Antarctica from South America so these and the other animals that shared their prehistoric habitats are extremely important to paleontologists because Antarctica's fossil record isn't as comprehensive as those on other continents and many of the bones we do
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find are isolated or fragmentary still the coexistence of all these Eocene creatures tells us that Antarctica was home to a variety of land mammals but why isn't that the case anymore what happened to green Antarctica well while Antarctica's land mammals were still kicking around some pretty big changes loomed on the horizon scientists are still working out the timeline of events but they think that by about fifty six million years ago Antarctica and South America had pulled away from each other then by about 40 million years ago Antarctica and Australia had
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become separated by an emerging Seaway this expanse of water which still exists today is sometimes called the Tasmanian gateway and at some point another Seaway formed the Drake Passage off the tip of the Antarctic Peninsula sometime between 36 and 23 million years ago so as time wore on and Arctica went from being a land bridge between South America and Australia to being an isolated continent the was set for a dominant new force in the southern ocean the Antarctic circumpolar current or AC see this current still
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swirls around Antarctica and hands down it's the most powerful current on earth it's volume is a thousand times bigger than that Amazon River and it chugs along at the breakneck speed of 40 centimeters per second in some locations propelled by winds and unimpeded by land the swirling current blocks warmer waters farther north keeping them away from the mainland it also dredges cold water from the ocean floor to the surface and those two factors work together creating a chilling effect on Antarctica climatologist think that the ACC is
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between 41 and 23 million years old but there's not a lot of agreement about how the formation of this current actually affected the drop in temperatures and the rise in glaciation on ancient Antarctica what we do know is that the late eocene in the early alig Essene was a time of global cooling at high latitudes in both hemispheres temperatures dropped by about 15 degrees Celsius around the world atmospheric carbon dioxide was decreasing possibly because large quantities of it were being absorbed by marine plankton or buried in ocean floor sediments this may
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have contributed to the worldwide cooling trend and the formation of the ACC could have forced temperatures in Antarctica to drop even further regardless we know that from about thirty six point five million years onward glaciers became more widespread across the continent as ice blanketed Antarctica surface many plant communities suffered a study of plant fossils from the Antarctic Peninsula found that it's plant diversity dropped by forty seven percent between the late Paleozoic seen slowly warmth loving trees and ferns found themselves replaced by
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temperate forests these were dominated by southern beech trees which we know had been living on the continent since the late cretaceous period based on fossilized leaf impressions in spora morphs and even their days were numbered their spore morphs tell us that there were southern beech trees on Antarctica as recently as 2.5 million years ago but today it's a treeless continent a polar desert whose remaining plants mostly consists of hardy mosses grasses lichens and algae clearly Antarctica's biodiversity took a hit after the Eocene and yet life
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continued to flourish on its two former neighbours after they split with Antarctica South America and Australia were both totally isolated from the rest of the world for millions of years and those two continents had something special in common marsupials new world possums originated in South America before some of them migrated north to Central and North America meanwhile Australia is world famous for its charismatic marsupials including the kangaroo wallaby and the now extinct thylacine and DNA evidence suggests that the common ancestor of today's
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marsupials lived in South America about 70 to 80 million years ago so from there marsupials spread through Antarctica and into Australia back when those three continents were still connected and as evidence of this journey they left behind the remains of marsupials like an dark toad Olaf's relatives of the mammals that Australia is famous for today so even though Antarctica has lost its big land animals it was once a forested pathway for life which is why even today our world retains the ecological fingerprints of a
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time when Antarctica was Green PBS Digital Studios wants to hear from you we do a survey every year that asks you about what you're into your favorite PBS shows like Aeons and things you'd like to see more of from PBS Digital Studios you even get to vote on potential new shows all of this helps us make more of the stuff you want to see the survey takes about 10 minutes and you might win a sweet t-shirt links in the description thanks for watching yawns which is produced by complexly if you want to keep imagining the world
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complexly with us check out crash course artificial intelligence hosted by jor-el ash over the course of 20 episodes we'll unpack the logic behind AI systems will even write and implement code into labs to program our very own AI check out the first video about the history of AI and the revolution that's happening today link is in the description and I gotta give a shout-out to this month's Yount ologist Patrick Seyfert Jake Hart John Davidson II and Steve to join them and our other IO Knights go to pledge your
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support at patreon.com slash Aeons and also thanks for joining me in the Konstantin Haase studio if you like what we do here then go subscribe at youtube.com slash Aeons you [Music]

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