By measuring the proportion of heavier hydrogen and oxygen isotopes along a strand of hair, scientists can construct a geographic timeline.

通过测量一束头发上较重的氢和氧同位素的比例，科学家可以构建一个地理时间轴。

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Oxygen isotopes vary with the water cycle, and sulfur with bedrock, so they're location proxies.

氧同位素会随着大气水循环而变化，硫同位素则根据地球岩床的不同而变化，通过它们我们就能确定地理位置。

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That water signature is in the form of oxygen isotopes, atoms of oxygen with different Numbers of neutrons.

这个特征就是氧的同位素，它是由氧原子和不同数量的中子组成的。

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There are also different oxygen isotopes in this meteorite than in younger Martian meteorites.

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To find out how warm the earth was before that, climatologists have had to resort to indirect methods, such as measuring tree-rings, or counting the different isotopes of oxygen in layers of polar ice.

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The researchers looked at the different types, or isotopes, of oxygen atoms trapped in the samples and, using a well-established technique, were able to infer water temperatures at the time the organisms built their shelly parts.

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