It’s the world’s most remote and isolated
continent. It’s home to glaciers, mountains, plants,
and penguins, but today, Antarctica is also noteworthy for what it doesn’t have. In modern Antarctica, there aren’t any trees,
or any 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
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 and 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, 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 that time when Antarctica was green. 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 Wilkes Land, in eastern Antarctica,
scientists have discovered sporomorphs--fossilized pollen and spores -- from ancient palm trees
and ferns. And 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 Wilkes 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, with an average winter temperature
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 sporomorphs and other
fossils from warm-weather plants in Antarctica that date way back 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-necked Glacialisaurus
and Cryolophosaurus, a crested carnivore. In those days, Antarctica was just one small
chunk of the supercontinent Gondawana, and was located a bit farther north than it is
now. But by about 100 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 Maximum, and we did a whole episode about it, because the theories about what
caused it -- and what made it stop -- are really complex, fascinating, and little scary During this period, the global average temperature
increased by 5 to 8 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 onto every continent, including Antarctica. And mind you, Antarctica is a really big 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,
sporomorphs and leaf impressions have been found from plants that are normally found
in temperate rainforests, like 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 Antarctic Peninsula,
paleontologists have recovered brood balls of ancient dung beetles. Those are balls of dung that female beetles
lay their eggs in. 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 belonged to the same order of marsupials as the modern colocolo opossum, a small and
adorable insect-eater that’s native to South America. Another Antarctic marsupial was Antarctodolops. First described in 1984, this opossum-like
critter was the first terrestrial mammal ever discovered in the continent’s 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 xenarthrans--the group of mammals that includes modern-day sloths--might have
lived in Antarctica. Xenarthrans originally evolved in South America,
as did the forerunners of a hoofed herbivore that’s been found in western Antarctic,
called Notiolofos,. The teeth of this creature tell us that it
was a browser, stripping twigs off if 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 Notiolofos 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 one-fourth
that size. And the fact that these two 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 Antarctodon, or “Antarctic Tooth.” Scientists think it was a kind of astrapothere,
an unusual group of extinct and mostly South American herbivores. The only Antarctodon fossils that have turned
up so far are teeth. But more complete skeletons of other astrapotheres
show that these animals looked kind of like tapirs. Some species had self-sharpening canine teeth
and ate a combination of soft plants and hard nuts. Others may have been semiaquatic, like modern-day
hippos. And paleontologists think Antarctodon was
yet another animal whose ancestors crossed into Antarctica from South America. So, these and the other animals that shared
their prehistoric habitat are extremely important to paleontologists. Because, Antarctica’s fossil record isn’t
as comprehensive as those on other continents, and many of the bones that we do 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 56
million years ago Antarctica and South America had pulled away from each other. Then by about 40 million years ago, Antarctica
and Australia had 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 million and
23 million years ago. So as time wore on, Antarctica went from being
a land bridge between South America and Australia to being an isolated continent. The stage was set for a dominant new force
in the Southern Ocean: The Antarctic Circumpolar Current, or ACC. This current still swirls around Antarctica,
and hands down, it is the most powerful current on earth. Its volume is 1000 times bigger than the 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. Climatologists think that the ACC is 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 and
early Oligocene 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 have contributed to the worldwide
cooling trend. And the formation of the ACC could’ve forced
temperatures in Antarctica to drop even further. Regardless, we know that from about 36.5 million
years onward, glaciers became more widespread across the continent. As ice blanketed Antarctica’s surface, many
plant communities suffered. A study of fossil plant samples from the Cross
Valley formation in the Antarctic Peninsula found that its plant diversity dropped by
47 percent between the late Paleocene and middle Eocene. Slowly, warmth-loving trees and ferns found
themselves replaced by 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 and sporomorphs. And even their days were numbered. Their sporomorphs 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 consist of hardy mosses, grasses, lichens
and algae. Clearly, Antarctica’s biodiversity took
a hit after the Eocene. And yet, life continued to flourish on its
two former neighbors. 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 opossums originated in South America
before some of them migrated north into Central and North America. Meanwhile, Australia is world-famous for its
charismatic marsupials, including kangaroos, wallabies and the now-extinct Thylacine. And DNA evidence suggests that the common
ancestor of today’s 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 Antarctodolops--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 time when Antarctica was green. Hey Fam! PBS Digital Studios wants to hear from YOU. We do a survey every year that asks about
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The Narrator mentions at 9:30 that beech trees still grew there 2.5 million years ago.
So you're saying it was the tools' fault? /s