時(shí)差N小時(shí):海洋殺手

Don: Time now for another episode of a Moment ofScience. Did you know? So Yael, did you know thatthere’ve been 23 mass extinctions since life begunon earth.

唐：又到了我們的科學(xué)時(shí)刻了。耶爾，你知道嗎?自從地球出現(xiàn)以來，她已經(jīng)歷了23次大規(guī)模的物種滅絕。

Yale: I know there’ve been a few extinctions, Don,but not that many.

耶爾：唐，我知道地球確實(shí)經(jīng)歷了幾次物種滅絕，但沒你說的那么多。

Don: Yep, many were prehistoric bacteria and other single-cell microorganisms, but in thepast 540 million years or so, there’ve been about 5 mass extinctions. Many are marine plantsand animals but also off-land organisms.

唐：是的。遠(yuǎn)古時(shí)候，地球上存在著大量的細(xì)菌和其它單細(xì)胞的微生物，但在過去的5億4000萬年內(nèi)，地球經(jīng)歷了5次大滅絕，滅絕的大多是海洋植物和海洋動(dòng)物，但也有一些陸地生物。

Yale: I know that the dinosaurs disappeared about 65 million years ago possibly due to a largemeteor crushing into earth and block out the sun. But what cause all those other extinctions?

耶爾：嗯，我聽說恐龍是在大約6千500萬年前滅絕的，可能是流星撞擊地球之后太陽光被遮擋造成的。其它幾次滅絕是什么原因?

Don: That’s been a mystery for a long time. But now some scientists think that most massextinctions have been driven by the rise and fall of sea level. That may sound strange. Butconsider that millions and millions years ago, a shallow sea covered the entire middle sectionof North America. That sea grew and shrank back several times. Each time it drained, it causedentire species of sea plants and creatures to die off. The last time it drained was around 65million years ago when the dinosaurs disappeared.

唐：那是一個(gè)埋藏許久的謎團(tuán)。但是，現(xiàn)在的一些科學(xué)家認(rèn)為，是海平面的上升或下降造成了這些大滅絕。這聽起來可能有點(diǎn)奇怪。但是，考慮到億萬年前覆蓋整個(gè)北美大陸中部的只是一層淺海，這片海域幾經(jīng)上升和回落。每次干涸，它都會(huì)造成整個(gè)海洋植物和動(dòng)物的消亡。它的最后一次干涸出現(xiàn)在6千500萬年前，正是在那個(gè)時(shí)候，恐龍徹底滅亡了。

Yale: OK, I understand that was sea vanishing would kill of the marine life. But did the sea’sdisappearing also have something to do with the dinosaurs going extinct?

耶爾：好吧，我知道了海洋消失的確會(huì)使海洋生物滅絕，但是也能使恐龍滅絕嗎?

Don: Maybe. When the sea disappears, it has big effect on climate. All that water provides heatand moisture. And when the sea drains, the climate becomes drier and colder. So the changingclimate may have combine with meteor impact to kill off the dinosaurs.

唐：也許是這樣的。當(dāng)海洋消失時(shí)，會(huì)對(duì)氣候產(chǎn)生巨大影響。海水可以提供熱量和濕氣。但是當(dāng)海洋干涸時(shí)，氣候會(huì)變得干燥和寒冷。因此，氣候變化和流星撞擊地球可能是恐龍滅絕的元兇。