字幕列表 影片播放 列印英文字幕 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 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 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!
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 更多分享 分享 收藏 回報 影片單字