VOA科学技术2023--Antarctica Was Once Home to Rivers, Forests

 

Antarctica Was Once Home to Rivers, Forests

Antarctica has not always been a land of ice and snow. Earth's southernmost continent once was home to rivers and forests full of life.

Scientists are using satellite observations and radar¹ imagery to look deep under the ice. The researchers report finding a large ancient landscape buried under the continent's ice sheet. It is full of valleys and ridges³, shaped by rivers before being covered by glaciers⁴ long ago.

The landscape is located in East Antarctica's Wilkes Land area bordering the Indian Ocean. It covers an area about the size of Belgium. The researchers said the landscape appears to date to at least 14 million years ago and perhaps beyond 34 million years ago, when Antarctica entered its deep freeze.

"The landscape is like a snapshot of the past," said Stewart Jamieson. He is a professor of glaciology at Durham University in England and co-leader of the study published in the journal Nature Communications.

"It is difficult to know what this lost world might have looked like before the ice came along, but it was certainly warmer back then," Jamieson added. "Depending how far back in time you go, you might have had climates that ranged anywhere from the climate of present-day Patagonia through to something more approaching tropical."

Such an environment likely would have been populated by wildlife, Jamieson said. But the area's fossil record is too incomplete to know which animals may have lived there.

The ice above the ancient landscape measures about 2.2 kilometers to 3 kilometers thick, said study co-leader Neil Ross. He is a professor of polar science and environmental geophysics at Newcastle University in England.

The researchers said the surface of the planet Mars is better known than the earth surface below the ice in Antarctica. They said one way to learn more would be to drill through the ice and take a piece of the earth below. This could uncover evidence showing ancient life, as was done with samples taken in Greenland dating back two million years ago.

Some earlier studies have uncovered ancient landscapes beneath Antarctica's ice including mountains. But the landscape discovered in the new study was the first of its kind.

Right before 34 million years ago, Antarctica's landscape and wildlife was likely similar to today's cold temperate⁵ rainforests. That includes places like Tasmania, New Zealand and South America's Patagonia area, Ross added.

Antarctica was once part of the Gondwana supercontinent that also included what is now Africa, South America, Australia, the Indian subcontinent and the Arabian Peninsula. But it eventually split off in a process called plate tectonics.

Jamieson said the researchers think that when Antarctica's climate was warmer, rivers flowed toward a continental⁶ coastline that was created as the other land masses broke away. When the climate cooled, he said, some small glaciers formed on hills next to the rivers, with valleys deepening as glaciers eroded⁸.

When the climate cooled even more, an ice sheet grew which covered the whole continent, Jamieson added. Eventually, "the landscape got preserved, likely for 34 million years."

Words in This Story

landscape — n. an area of land that has a particular quality or appearance

ridge² — n. a long area of land that is on top of a mountain or hill

snapshot — n. a quick view or a small amount of information that tells you a little about what someone or something is like

range — n. a group or collection of different things or people that are usually similar in some way

tropical — adj. of, relating to, occurring in, or used in the tropics

erode⁷ — v. to gradually destroy or to be gradually destroyed by natural forces

1 radar   

n.雷达，无线电探测器

参考例句：

• They are following the flight of an aircraft by radar.他们正在用雷达追踪一架飞机的飞行。
• Enemy ships were detected on the radar.敌舰的影像已显现在雷达上。

2 ridge   

n.山脊；鼻梁；分水岭

参考例句：

• We clambered up the hillside to the ridge above.我们沿着山坡费力地爬上了山脊。
• The infantry were advancing to attack the ridge.步兵部队正在向前挺进攻打山脊。

3 ridges   

n.脊( ridge的名词复数 )；山脊；脊状突起；大气层的)高压脊

参考例句：

• The path winds along mountain ridges. 峰回路转。
• Perhaps that was the deepest truth in Ridges's nature. 在里奇斯的思想上，这大概可以算是天经地义第一条了。

4 glaciers   

冰河，冰川( glacier的名词复数 )

参考例句：

• Glaciers gouged out valleys from the hills. 冰川把丘陵地带冲出一条条山谷。
• It has ice and snow glaciers, rainforests and beautiful mountains. 既有冰川，又有雨林和秀丽的山峰。 来自英语晨读30分（高一）

5 temperate   

adj.温和的，温带的，自我克制的，不过分的

参考例句：

• Asia extends across the frigid,temperate and tropical zones.亚洲地跨寒、温、热三带。
• Great Britain has a temperate climate.英国气候温和。

6 continental   

adj.大陆的，大陆性的，欧洲大陆的

参考例句：

• A continental climate is different from an insular one.大陆性气候不同于岛屿气候。
• The most ancient parts of the continental crust are 4000 million years old.大陆地壳最古老的部分有40亿年历史。

7 erode   

v.侵蚀，腐蚀，使...减少、减弱或消失

参考例句：

• Once exposed,soil is quickly eroded by wind and rain.一旦暴露在外，土壤很快就会被风雨侵蚀。
• Competition in the financial marketplace has eroded profits.金融市场的竞争降低了利润。

8 eroded   

adj. 被侵蚀的，有蚀痕的 动词erode的过去式和过去分词形式

参考例句：

• The cliff face has been steadily eroded by the sea. 峭壁表面逐渐被海水侵蚀。
• The stream eroded a channel in the solid rock. 小溪在硬石中侵蚀成一条水道。