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Then there was the final clue from the KT boundary a high concentration of fern spores.
后來第三紀界線層中又發現了最后一條線索，大量蕨類植物孢子。
Ferns flourish whenever all other plants have been killed off by some environmental devastation.
每當其它植物因為環境破壞而遭到毀滅時，蕨類植物卻因此而得到興盛。
So the predominance of fern spores known as a fern spike suggested something had wiped out every plant on the planet.
所以蕨類植物孢子的優勢，即所謂的蕨類高峰，說明有些東西消滅了地球上所有植物。
Fern spikes were found all over the world such as in New Zealand
蕨類高峰出現在全世界各地，比如新西蘭，
and this I think became stronger and stronger evidence that there was something like global darkness caused by an impact.
我認為這一證據越來越明顯，它說明大碰撞引起了全球黑暗這樣的事件。
So the theory grew up that vast amounts of dust created by the impact must have blocked out the sun.
所以這一理論認為由于大碰撞產生的大量煙塵遮住了太陽。
This could have plunged the world into freezing darkness for months or years.
這使得世界幾個月甚至幾年被冰冷和黑暗包圍著。
Any dinosaurs which had escaped burning either froze or starved to death.
在大火中僥幸逃生的恐龍，不是凍死，就是餓死。
But the mammals were small and could burrow to escape the heat and the cold.
不過哺乳動物的體型很小，它們在地洞中躲過了極熱和極冷的環境。
When conditions recovered they would emerge to inherit the earth.
當環境恢復正常之后，它們便現身并接管地球。
It was an elegant theory and there was only one thing missing
這種理論似乎很有說服力，只是缺少一樣東西，
the impact should have left a crater, two hundred kilometres across.
那就是大碰撞會留下一個至少200公里寬的隕石坑。
To be certain the theory was right, they had to find it.
為了證明這種理論，人們必須找到這個大坑。
