当一个物种灭绝时，它会极大地改变生物多样性的状况。
When a species goes extinct, it dramatically changes the landscape of biodiversity.
一个物种一旦灭绝就永远消失了。
边界粘土层被科学家用来确定一个灭绝物种衰落的速度。
Boundary clay layers are used by scientists to determine the rate at which an extinct species declined.
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