万物简史 第497期:多灾多难的生命进程(17)

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Cooling seems to be associated with at least three of the big extinction² events — the Ordovician, Devonian, and Permian, 变冷似乎至少与三次大灭绝事件有关——奥陶纪事件、泥盆纪事件和二叠纪事件，

but beyond that little is agreed, including whether a particular episode happened swiftly or slowly. 但是，除此以外，大家几乎没有共识，包括某次事件是快速发生的还是缓慢发生的。

Scientists can't agree, for instance, whether the late Devonian extinction — the event that was followed by vertebrates moving onto the land, 比如，泥盆纪灭绝事件——那个事件以后，脊椎动物迁移到了陆地，

happened over millions of years or thousands of years or in one lively day. 是在几百万年里发生的，还是在几千年里发生的，还是在热热闹闹的一天里发生的，科学家们的看法不一。

One of the reasons it is so hard to produce convincing explanations for extinctions is that it is so very hard to exterminate³ life on a grand scale. 对灭绝提出令人信服的解释的难度如此之大，原因之一是要大规模灭绝生命是非常困难的。

As we have seen from the Manson impact, you can receive a ferocious⁴ blow and still stage a full, if presumably somewhat wobbly, recovery. 我们从曼森撞击事件中已经看到。你可能受到猛烈的一击，但仍可以充分恢复过来，虽然觉得有点挺不住。

So why, out of all the thousands of impacts Earth has endured, was the KT event so singularly devastating⁵? 因此，地球已经忍受了几千次撞击。为什么偏偏6500万年前的KT事件的破坏性那么大，足以使恐龙遭受灭顶之灾呢？

Well, first it was positively⁶ enormous. 哎呀，首先，它确实厉害。

It struck with the force of 100 million megatons. Such an outburst is not easily imagined, but as James Lawrence Powell has pointed⁷ out, 它的撞击力达到1亿亿吨。这样的爆炸是术容易想像的，但正如詹姆斯·劳伦斯指出的，

if you exploded one Hiroshima-sized bomb for every person alive on earth today you would still be about a billion bombs short of the size of the KT impact. 要是你朝今天地球上的每个活人爆炸一颗广岛型原子弹，你离KT撞击事件的威力仍相差大约10亿颗这类炸弹。

But even that alone may not have been enough to wipe out 70 percent of Earth's life, dinosaurs⁸ included. 然而，仅此一项也许仍不足以消灭地球上70%的生命，包括恐龙在内。

 

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