Name: 南極は実は熱帯で緑が多かった (Antarctica Was Actually Tropical and Green)
Uploaded: 2021-01-14T09:38:49.000Z
Duration: 11 min
Description: VoiceTubeの動画で発音を聞きながら英語表現を覚えよう！学べる英語：

程度の副詞

There was a time when the great southern landmass wasn’t just covered in ice-glaciers and

基礎受動態

penguins. It was filled with forests, flowers and all sorts of animal species. It even had

a completely different climate. So, how did we end up here?

Let’s take a brief trip in time and find out what happened. Around 550 - 180 million

years ago, Antarctica was part of a supercontinent called Gondwana. It was connected to South

America, Australia, Africa, the Arabian Peninsula, and the Indian subcontinent. The break-up

started in the Jurassic period. They just couldn’t get along. Around 180 million years

ago, Antarctica began moving to the bottom of the globe.

According to fossil records found below the ice-caps, the icy continent was once a very

hot place. In fact, it got so warm that the climate became tropical, like the one we see

today around the Equator. About ½ mile below the seabed at Wilkes Land

in Eastern Antarctica, scientists made a great discovery. They found fossils containing pollen

from plants that only flourish in the tropical environments we see today. They also found

the same pollen going back millions of years close to the Arctic Circle. But I’ll get

into those in a bit. Now, we all know that tropical vegetation

can’t stand cold weather. So, it’s believed that the eastern part of Antarctica didn’t

have frosty winters. The average winter temperatures were similar to the ones in South America.

As it turns out, this is a repeating pattern. Everyone previously thought that Antarctica

reached high temperatures for the first time just before the Eocene period, (approximately

56 million years ago). But after research, paleontologists found more fossilized plants

that go all the way back to the Devonian Period – somewhere around 419 – 358 million years

ago. Ah, what’s a couple of million here or there?

Now, around 100 million years back, the earth went through a massive long-lasting heatwave

- scientifically known as the Paleocene-Eocene thermal maximum. During that time, the global

average temperature increased. That resulted in changes to vegetation.

Antarctica was filled with all sorts of trees, plants, and flowers. Even palm trees made

an appearance, alongside relatives of today’s tropical baobab trees. The climate of the

continent became flexible. During the Eocene period, Antarctica supported a variety of

ecosystems. At high elevations and further inland, several

plants present in temperate rainforests were found. One of them was the Southern Beech.

Fossils that were found on the continent preserved the biology and chemistry of the flora. That

helped researchers understand how some of the plants survived the mass extinction, while

others didn’t. However, vegetation wasn’t the only thing

spreading all around the icy continent. On Seymour Island, which is around the tip of

the Graham Land on the Antarctic Peninsula, scientists discovered brood balls, a unique

structure that dung beetles lay their eggs in. That means these little guys had to be

feeding on something. Later, scientists found remains and isolated

teeth, showing that several mammals lived in the area. A few of them all belonged to

the same type of ancient marsupials, like the modern colocolo opossum. It was a tiny

insect-feeder native to South America. Another type of marsupial found was the blah-blah-blah-blah,

also pronounced Antarctodolops. It was the first recorded fossil, discovered in 1984.

Some described it as a critter resembling an opossum. Um, for those of you keeping score,

a “critter” is a close relative of the “varmint”.

Then, a toe bone was found, making scientists believe that a group of mammals called Xenarthra

also lived in the continent. This family included the sloths we have today.

These guys first evolved in South America. But, so did the descendants of a hoofed mammal

found in Antarctica called Notiolofos. These creatures fed on tiny tree branches and saplings.

Scientists discovered their diet by analyzing the animal’s teeth, which were relatively

small in size. When they investigated the fossils further,

they found that there were two types of Notiolofos. The Notiolofos Arquinotiensis and the Notiolofos

Regueroi. Hope you were paying attention -- that’s the last time I’m saying those Latin names…jeesh.

The first one weighed a little less than 510 pounds, maybe 508--while the other one was

only 130 pounds. Because of their size difference, it’s believed that both mammals could be

specialists. That means that they fed on different types of plants to avoid competing for food.

Another hoofed creature that entered West Antarctica from South America during the early

Eocene period was the Antarctodon. It belonged to an unusual group of now-extinct mammals.

It lived in what we know now as Seymour Island. Only fossilized teeth of these guys were found.

But somewhat complete skeletons of other mammals in this family showed that they resembled

tapirs. Some of these species also had sharp canine

teeth. They were able to feed on both nuts and soft plants. It’s speculated that a

few of them could be semiaquatic, like otters and beavers. But the fossil record in Antarctica

is troubling. It isn’t as complete as those in other continents. Some of the bones found

are either fragmented or isolated. The good thing is, the yet to be discovered

fossils might be well-preserved under the ice glaciers. The existence of these creatures

during the Eocene period shows that Antarctica was a great habitat for land mammals. So,

how did the tropical greenery become a frozen, unwelcoming environment? Real estate prices?

Scientists are still trying to understand the timescale of when things changed. Since

those animals co-existed, changes began happening slowly.

They believe that approximately 56 million years ago, South America began separating

itself. 16 million years later, Australia and Antarctica began drifting apart in the

sea. Between 36 to 23 million years back, another natural channel emerged – the Drake

Passage. That also proves that the continental drift happened gradually.

Antarctica was a land bridge between Australia and South America. As it broke apart from

South America, and later from Australia, it started moving south. That made room for a

new force to emerge in the Southern Ocean called the Antarctic Circumpolar Current.

The ACC flows clockwise: from the west to the east. It’s considered the most powerful

current in the world to this day. It carries between 5.8 to 6.4 billion cubic

feet of water every second. Since there’s no land to block the current, and because

of the way it flows, it prevents warm waters from reaching Antarctica. The ACC also brings

cold water from the seabed of the ocean to the surface. That resulted in a drop in temperatures

on the isolated continent. There’s insufficient evidence to show a

connection between the rise of ice glaciers in Ancient Antarctica and the ACC. But, climatologists

believe that the current is 41 to 23 million years old.

Towards the end of the Eocene and the beginning of Oligocene Period, global cooling started

taking place. The temperatures dropped at high latitudes in both the Arctic Circle and

Antarctica. The carbon dioxide levels in the Earth’s

atmosphere had dropped significantly. According to professor Stephen Pekar, approximately

55 million years ago, there were more than 1,000 parts per million of carbon dioxide

in the Earth’s atmosphere. During that time, the high temperatures on earth melted all

of its ice caps. That caused the sea levels to rise about 200 feet higher than they are

today. Scientists were trying to figure out why our

atmosphere went through such unpredictable fluctuations in CO2. Some theorists suggest

that during certain periods, the tectonic plates moved and triggered carbonate-rich

rocks and other remains to release carbon dioxide. This caused the air to heat up, and

the ice-caps melted. But then, the cycle continued. 34 million

years ago, the levels dropped from 1,000 to 760 ppm. 14 million years later, they dropped

below 300 ppm. The carbon dioxide was absorbed through natural processes which contributed

to the global cooling effect. Over geological times, atmospheric pressures

and carbon dioxide levels were linked. When the first one rises, the second one follows.

The ice glaciers in Antarctica began to form from 36.5 million years ago and onward. They