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。

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

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随着大量的水通过蒸发被抽离，并以雪的形式沉淀形成冰川冰，海洋中氧同位素的比率就发生了变化。

The oxygen isotope ratio of the ocean changes as a great deal of water is withdrawn from it by evaporation and is precipitated as snow to form glacial ice.

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除了比对氧同位素的季度变化之外，渡边刚及其同事们还比对了年度的变化。

Besides finding season-to-season variations in oxygen isotopes, Watanabe and his colleagues discerned year-to-year variations.

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