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Mass extinctions 大灭绝 Small but deadly 陨石很小不过危害却很致命 The biggest extinction in history was probablycaused by a space rock that changed the climate 历史上规模最大的一次物种灭绝，也许是由于陨石坠落导致的气候变化而造成 AS EVERY schoolchild knows, the dinosaurs were wiped out in an instant, when a rock fromouter space hit what is now southern Mexico. 就像每个小学生知道的那样，当一块天外陨石坠落到现今的墨西哥南部地区之后，恐龙就那在一瞬间遭受了灭顶之灾。 That happened 66m years ago, at the end of the Cretaceous period. 这一切就发生在6600万年前的白垩纪末期。 Well-informed schoolchildren also know that this mass extinction was neither unique northe biggest. 一些博学的小学生还知道这次物种大灭绝既不是历史上唯一的一次，也不是历史上最大的一次。 The geological record speaks of four others since animal life became complex at thebeginning of the Cambrian period 541m years ago. 地质学档案记录了5亿4100万年前寒武纪物种多样化以来的另外四次物种大灭绝。 What neither these clever schoolchildren nor anyone else knows, however, is whether theseextinctions had similar causes. | 
