萬物簡史 第42期:埃文斯牧師的宇宙(11)

At this point, about 4.5 billion years ago, an objectthe size of Mars crashed into Earth, blowing outenough material to form a companion sphere, theMoon. Within weeks, it is thought, the flung materialhad reassembled itself into a single clump, andwithin a year it had formed into the spherical rockthat companions us yet. Most of the lunar material, itis thought, came from the Earth’s crust, not its core,which is why the Moon has so little iron while wehave a lot. The theory, incidentally, is almostalways presented as a recent one, but in fact it wasfirst proposed in the 1940s by Reginald Daly of Harvard. The only recent thing about it ispeople paying any attention to it.

在這個時刻，大約在45億年以前，一個火星大小的物體撞上了地球，炸飛了足夠的材料來形成一顆伴星--月球。據(jù)認為，不出幾個星期，被炸飛的材料已經(jīng)重新聚成一團;不出一年，它變成了那個現(xiàn)在還陪伴著我們的巖石球體。據(jù)認為，構(gòu)成月球的大部分材料來自地殼，不是地核，這就是月球上極少有鐵的原因，而地球上鐵卻很多。順便說一句，這個理論幾乎總是被說成是最近提出的，而事實上，它最初由哈佛大學的雷金納德•戴利于20世紀40年代提出。關(guān)于這個理論，惟一最近的事兒就是人們已經(jīng)不大重視它了。

When Earth was only about a third of its eventual size, it was probably already beginning toform an atmosphere, mostly of carbon dioxide, nitrogen, methane, and sulfur. Hardly the sort ofstuff that we would associate with life, and yet from this noxious stew life formed. Carbondioxide is a powerful greenhouse gas. This was a good thing because the Sun was significantlydimmer back then. Had we not had the benefit of a greenhouse effect, the Earth might wellhave frozen over permanently, and life might never have gotten a toehold. But somehow lifedid.

當?shù)厍蜻€是它最終大小的大約三分之一的時候，它很可能已經(jīng)開始形成大氣，主要由二氧化碳、氮、甲烷和硫組成。我們幾乎不會把這些東西與生命聯(lián)系起來;然而，在這有毒的混雜物中，生命形成了。二氧化碳是一種強有力的溫室氣體。它是一樣好東西，因為當時太陽已經(jīng)弱多了。要是我們沒有受益于溫室效應，地球很可能已經(jīng)永久被冰雪覆蓋。生命也許永遠找不到一塊立足之地。但是，生命以某種方式出現(xiàn)了。

For the next 500 million years the young Earth continued to be pelted relentlessly by comets,meteorites, and other galactic debris, which brought water to fill the oceans and thecomponents necessary for the successful formation of life. It was a singularly hostileenvironment and yet somehow life got going. Some tiny bag of chemicals twitched andbecame animate. We were on our way.

在之后的5億年里，年輕的地球繼續(xù)受到彗星、隕石和銀河系里其他碎塊的無情撞擊。這個過程產(chǎn)生了蓄滿海洋的水，產(chǎn)生了成功形成生命所必不可少的成分。這是個極不友好的環(huán)境，然而生命還是以某種方式開始了。有一小袋化學物質(zhì)抽動一下，變成了活的。我們快要來到這個世界上了。

Four billion years later people began to wonder how it had all happened. And it is there that ourstory next takes us.

40億年以后，人們開始想，這一切到底是怎么發(fā)生的?下面，我們就來講講這個故事。