托福閱讀資料之什么是南極地衣

　　Although ninety-eight percent of Antarctica is covered by thick ice, there are bare patches where the rocky surface shows through. These so-called “dry valleys” are some of the most inhospitable places on Earth. Air temperature is well below freezing, and it’s dry as a desert because arid, hurricane-force winds suck the snow and other moisture away.

　　If you were a microorganism in one of Antarctica’s dry valleys, where would you hide to escape the biting, arid wind?

　　For a cryptoendolith, the answer is inside a rock. These Antarctic cryptoendoliths are a type of lichen whose very name translates as “hiding inside rocks.” Even in this cold, dry land, these lichen need a certain amount of warmth and moisture to survive. How does living inside a rock help them keep warm and wet?

　　These lichen live a fraction of an inch inside pieces of porous sandstone. They prefer north-facing stones, which absorb sunlight and heat up during the day.

　　Even if the air stays bitterly cold, these sunbaked rocks can warm enough to melt whatever tiny patches of snow have escaped the thirsty wind. The water is quickly absorbed by the porous rock, and it can stay inside for weeks–freezing and re-melting as the rock warms and chills.

　　Of course the lichen freeze and thaw too, as much as several times an hour during a particularly rough day. But they get just enough heat, and just enough moisture, to stay alive. Which is what survival is all about anyway.

　　譯文

　　提到南極洲，眼前浮現(xiàn)的是一片荒涼的冰域，毫無生命氣息，凜冽刺骨的風(fēng)拍打著這塊土地。

　　盡管南極洲98%的土地都被厚厚的冰覆蓋著，但巖石表面仍然有一些次生裸地。這些所謂的“干旱河谷”是地球上十分荒涼的地方。那里的氣溫遠(yuǎn)遠(yuǎn)低于結(jié)冰點，同時由于強大的颶風(fēng)吸收了雪和其他的水分，這又是一個干旱的荒漠。

　　假如說您是南極洲干谷里的一種微生物，是否能想到在哪里能躲過這干燥刺骨的風(fēng)?