Each mass extinction may have had a different cause.

每一次大灭绝可能都有不同的原因。

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Once every 100 million years or so, an even larger asteroid may cause a mass extinction; most scientists believe a six-mile-wide asteroid doomed the dinosaurs 65 million years ago.

每隔1亿年左右，一颗更大的小行星可能导致物种大灭绝。大多数科学家相信一颗6英里直径的小行星在6500万年前使恐龙灭绝。

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