英語(yǔ)聽(tīng)力文摘 南極有蒼蠅？

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南極有蒼蠅?

Sometimes the biggest finds are the smallest finds. Researchers examining a segment of siltstone taken from ground along the Beardmore glacier in Antarctica found something unexpected. They found a fly.

Well, not exactly a fly. They found a fly fossil–it’s a segment of the exoskeleton, the protective shell, of a fly larva. While the larvae are still growing, they are protected by a thin shell. And where there’s larval shell, there are flies. So what are flies doing in Antarctica? It’s much too cold there for flies. And the closest fly-friendly location, South America, is thousands of miles away.

Part of the answer is that the fly fossil is ancient–it was found with a number of other fossilized things that have been dated between three million and seventeen million years old. It’s possible that the fly lived during a period when sea levels were much lower there than they now are. Lower sea levels means wider continents –think of standing on the edge of a beach and having the water pull back. And wider continents means it’s more likely that living things might travel across the gap.

Or maybe not. Maybe flies are much older than anyone thought. We know that what we now call Antarctica was once connected to both South America and Australia. But that was around eighty million years ago, and flies aren’t thought to be that old.

Whatever the answer is, something in our understanding of the continents, the seas, or fly evolution has to be fixed. That’s one of the best things about science–a really big change can come from the discovery of something really small.

有時(shí)候，重大發(fā)現(xiàn)源于很小的發(fā)現(xiàn)。研究人員在南極比爾德莫爾冰川采集回來(lái)的一塊粉砂巖中意外地發(fā)現(xiàn)了蒼蠅。

準(zhǔn)確地說(shuō)，不是蒼蠅，而是蒼蠅的化石。一塊保護(hù)幼蟲(chóng)的外骨骼。在薄殼的保護(hù)下，幼蟲(chóng)還在發(fā)育。幼蟲(chóng)的蛹?xì)ぷC明了蒼蠅的存在。那么，蒼蠅怎么會(huì)在南極呢?南極冰冷的氣候不適宜蒼蠅生長(zhǎng)啊!反而，最適宜蒼蠅生存的地方——南非，卻遠(yuǎn)在幾千里之外。

正解可能是因?yàn)檫@塊蒼蠅的化石和一起發(fā)現(xiàn)的其它化石可以追溯到300萬(wàn)到700萬(wàn)年前了。很可能，蒼蠅生長(zhǎng)的那個(gè)時(shí)期，海水沒(méi)有現(xiàn)在那么高，這意味著陸地面積更大。想象自己站在海邊，浪打回來(lái)。廣闊的陸地面積讓生物更有可能跨越于大陸間。

另種可能是蒼蠅在地球上生存的時(shí)間比我們想象的還要久遠(yuǎn)。要知道，現(xiàn)在的南極曾經(jīng)和南美大陸及澳大利亞大陸是接壤的。但這也是8000萬(wàn)年前的事了，那時(shí)候，蒼蠅已經(jīng)在地球上了?

不管答案究竟是什么，我們所認(rèn)識(shí)的大陸、海洋、蒼蠅進(jìn)化的常識(shí)之一要得以修正。這就是科學(xué)的妙處，一個(gè)小小的發(fā)現(xiàn)或許能推翻重大定論。