The evidence lies in ocean mud, in fossil pollen, and in changes in ratio of chemical isotopes that record shifts in temperature.

证据就存在于海洋泥土，花粉化石和记录温度变化的化学同位素比值变化之中。

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Now, a team has attempted to solve the mystery by comparing the ratio of two isotopes, or forms, of chlorine in lunar and terrestrial rocks.

目前，一个研究小组打算通过对比月球和地球岩石中氯的两种同位素，或两种形式的氯来解决这个疑团。

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But the new study shows that the ratio of oxygen and nitrogen isotopes found in the solar wind is different from the ratio here on earth, or on the moon or Mars.

不过这一最新的研究发现，太阳风当中的氧和氮同位素比例与地球、月球或火星上的比例不同。

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And by looking at the difference in the ratio of isotopes it was concluded that Mars lost 99.99 percent of its atmosphere.

NPR: Revisiting the Viking Missions to Mars

The scientists know the gases are of cosmic origin because they contain an unusual ratio of isotopes - different types of the same atom.

BBC: ET gases caged on Earth

By analysing the isotopic composition of hydrocarbon molecules from plant waxes of the period, he found what looks like a spike in the amount of recently non-biological carbon (which has a distinctive ratio of light isotopes to heavy ones), lasting between 10, 000 and 20, 000 years.

ECONOMIST: A geological burp may have led to the dinosaurs�� domination