嵌入加拿大古代岩石的微粒为引发地球大灭绝的原因提供了新的线索。
Tiny particles embedded in ancient Canadian rocks have provided new clues about what might have triggered Earth's deadliest mass extinction.
化石记录表明，在地球有动物居住的所有时期，已经有五次大灭绝发生，恐龙是最近的一次。
The fossil record indicates that in all the time that animals have inhabited Earth, there have been five great mass extinctions, dinosaurs being the most recent.
科学家将白垩纪末期的大灭绝与地球上的陨石撞击联系起来。
Scientists have linked the mass extinction at the end of the Cretaceous with a meteorite impact on Earth.
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