The adult tree gives us shade, oxygen and natural beauty.

大树为我们提供荫蔽、制造氧气，让我们享受大自然的美丽。

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They then used local snowfall records to find the relationship between precipitation and the proportion of heavy oxygen in tree rings for the years covered by the weather records.

他们然后使用当地的降雪记录来寻找有气象记录的年代里降雪量和树木年轮中氧元素同位素的比率之间的关系。

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One mature tree can produce enough oxygen for up to 18 people, depending on the size and type of tree.

一棵成年树，可以为多达18人供氧，具体数量依树的大小和种类有所不同。

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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.

ECONOMIST: The hole story of global warming