Placeholder Image

字幕列表 影片播放

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

  • 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 Periodsomewhere 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 “critteris a close relative of thevarmint”.

  • 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 namesjeesh.

  • 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 emergedthe 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

  • started spreading across the continent, and vegetation began to disappear. But here’s

  • what’s interesting. According to a fossil study that examined plant samples from the

  • area, scientists found that the variety of plants decreased by 47%. This started at the

  • end of the Paleocene epoch – 58 million years back, until the mid-Eocene Period – 40

  • million years ago. Tropical plants were slowly replaced by temperate

  • forests filled with Southern Beech trees. The later ones disappeared 2.5 million years

  • ago. Today Antarctica is a deserted continent.

  • The closest thing to flora there is, is moss, algae, and lichen.

  • While Antarctica became an isolated landmass without much life, Australia and South America

  • thrived. One thing the 3 had in common was the marsupials. In Australia, the marsupials

  • multiplied. Some of them were kangaroos, the now extinct Thylacine, and wallabies. Fossil

  • records show that kangaroos date 20 million years back, but they weren’t hopping at

  • first; they just clung to tree branches. New DNA evidence shows that the oldest marsupial

  • lived in South America 70 – 80 million years ago. It’s believed that they migrated from

  • South America all the way to Antarctica and crossed over to Australia while they were

  • still connected. That’s how similarities in species exist

  • in both continents. But of course, they evolved differently in their new habitats.

  • Hey, if you learned something new today, then give the video a like and share it with a

  • friend! And here are some other cool videos I think you'll enjoy. Just click to the left

  • or right and stay on the Bright Side of life!

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

字幕與單字

單字即點即查 點擊單字可以查詢單字解釋

B1 中級

南極洲其實是熱帶和綠色的。 (Antarctica Was Actually Tropical and Green)

  • 2 0
    林宜悉 發佈於 2021 年 01 月 14 日
影片單字