人们已经得到了6500万年前白垩纪灭绝事件很好的证据。
So 65 million years ago they've got very good evidence of the cretaceous exctinction event.
在这一系列周期性物种灭绝事件里，白垩纪晚期恐龙和菊石的灭绝仅仅是其中一个比较严重的事件。
The late Cretaceous extinction of the dinosaurs and ammonoids was just one of the more drastic in a whole series of such recurrent extinction episodes.
天外来客对地球的撞击与白垩纪的物种灭绝事件有着最为密切的联系。
An extraterrestrial impact is most closely linked to the Cretaceous extinction event.
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