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Then there was the final clue from the KT boundary a high concentration of fern spores.
后来第三纪界线层中又发现了最后一条线索，大量蕨类植物孢子。
Ferns flourish whenever all other plants have been killed off by some environmental devastation.
每当其它植物因为环境破坏而遭到毁灭时，蕨类植物却因此而得到兴盛。
So the predominance of fern spores known as a fern spike suggested something had wiped out every plant on the planet.
所以蕨类植物孢子的优势，即所谓的蕨类高峰，说明有些东西消灭了地球上所有植物。
Fern spikes were found all over the world such as in New Zealand
蕨类高峰出现在全世界各地，比如新西兰，
and this I think became stronger and stronger evidence that there was something like global darkness caused by an impact.
我认为这一证据越来越明显，它说明大碰撞引起了全球黑暗这样的事件。
So the theory grew up that vast amounts of dust created by the impact must have blocked out the sun.
所以这一理论认为由于大碰撞产生的大量烟尘遮住了太阳。
This could have plunged the world into freezing darkness for months or years.
这使得世界几个月甚至几年被冰冷和黑暗包围着。
Any dinosaurs which had escaped burning either froze or starved to death.
在大火中侥幸逃生的恐龙，不是冻死，就是饿死。
But the mammals were small and could burrow to escape the heat and the cold.
不过哺乳动物的体型很小，它们在地洞中躲过了极热和极冷的环境。
When conditions recovered they would emerge to inherit the earth.
当环境恢复正常之后，它们便现身并接管地球。
It was an elegant theory and there was only one thing missing
这种理论似乎很有说服力，只是缺少一样东西，
the impact should have left a crater, two hundred kilometres across.
那就是大碰撞会留下一个至少200公里宽的陨石坑。
To be certain the theory was right, they had to find it.
为了证明这种理论，人们必须找到这个大坑。
