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Revealed, the gas that time forgot

作者:海褚    发布时间:2019-03-07 07:03:17    

By Jeff Hecht XENON gas from the primordial cloud that formed the Solar System is lurking deep in the Earth’s mantle. The finding means that researchers might have to revise their ideas about how our planet’s atmosphere formed. Geologists think that the Earth’s atmosphere was born as primordial gas escaped from the Earth’s mantle. Our atmosphere is known to have more heavy isotopes of xenon than the Sun, because lighter atoms escaped from the young planet while heavier xenon isotopes accumulated as they were formed by the decay of radioactive atoms in the mantle. So Mark Caffee of the Lawrence Livermore National Laboratory in California expected gas escaping from deep wells in the American Southwest and Australia to have the same isotope ratios as today’s atmosphere. But to his surprise, he found that samples contained more light isotopes than the atmosphere. This suggests some of the xenon was left over from the raw material that formed the planets, he says (Science, vol 285, p 2115). The measurements do not reveal where the ancient gases come from. “But it is tempting to say that they came from the lower mantle, and that the lower mantle still has a lot of its primitive volatiles,” says Caffee. Scientists will have to rethink gaseous exchange between the Earth and atmosphere,

 

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