Passage 1 A hidden landscape has been unveiled under the East Antarctic ice sheet. A landscape shaped by rivers and glaciers over millions of years seems to have been preserved beneath the East Antarctic ice sheet. The finding suggests that this area of Antarctica may have been covered in ice for more than 30 million years. Apart from a few mountain peaks, almost all the geological features of Antarctica are covered in a sheet of ice more than 2 kilometres thick. Radar measurements have revealed the broad contours of this hidden landscape, but details remain largely obscure. Now, Stewart Jamieson at Durham University in the UK and his colleagues have used a satellite radar to get a new view of the surface of the East Antarctic ice sheet. Jamieson says, “Any ice sitting on top is going to very generally undulate over those mountains or those hills.” Then they checked the topography against direct measurements from ice-penetrating radar recorded by aerial surveys. Together, the radar measurements revealed a region dubbed Highland A, which was distinct from the surrounding landscape. The 32,000-square-kilometre area features three blocks of land, separated by “fjords” between the blocks of land that were shaped by rivers flowing through rifts created by the break-up, then carved out further by glaciers when the climate cooled around 34 million years ago. The researchers posit that these features describe a geological history stretching back to the separation of Antarctica from the Gondwana supercontinent some 180 million years ago. As cooling accelerated and the ice sheet grew above the region, the topography in surrounding areas was scrubbed away. But Jamieson says the features of Highland A were preserved because the glaciers formed a cold base beneath the ice sheet that locked onto the rock and prevented erosion. “The glaciers switch from being an erosive mechanism to being a protective mechanism.” The preserved landscape also suggests that the region has been covered in ice for at least 14 million years, if not 34 million years, says Jamieson. If you had a huge retreat of the ice sheet, then you would have got the features washed away. The findings could improve models of how the climate of East Antarctica has changed over time as climate change raises average temperatures. What can we know about the hidden landscape under the East Antarctic ice sheet A. It has been under ice for exactly 30 million years. B. Most of its geological features are visible. C. It was shaped by rivers and glaciers over a long time. D. Radar measurements can clearly show all its details. What is special about Highland A A. It is part of the Gondwana supercontinent. B. It has a distinct landscape from the surrounding area. C. Its features were formed about 180 million years ago. D. It was the first area discovered under the ice sheet. Why were the features of Highland A preserved A. Because the glaciers changed from an erosive to a protective role. B. Because the ... ...
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