They breathe through uncomfortable respirators or carry heavy oxygen tanks on their backs.

他们或通过防毒面罩，或携带沉重的氧气瓶进行呼吸。

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Researchers said the zircon's high level of heavy oxygen isotopes suggest it was cooled by surface water after it formed.

研究人员说锆石的高标准重氧同位素暗示了它形成之后靠地表水来冷却。

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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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Our sun is enriched with heavy elements, with metals, and oxygen, and so forth, that have to have been made inside another star that died before our sun and our solar system formed.

NPR: What Makes Our Solar System Special?

Before it can be released back into the nearby watercourses it has to meet stringent standards, including maximum levels of ammonia, heavy metals and any chemicals that might cause oxygen depletion.

ECONOMIST: The charms of modern landfills