XENON gas from the primordial cloud that formed the Solar System is lurking
deep in the Earth鈥檚 mantle. The finding means that researchers might have to
revise their ideas about how our planet鈥檚 atmosphere formed.
Geologists think that the Earth鈥檚 atmosphere was born as primordial gas
escaped from the Earth鈥檚 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鈥檚 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).
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The measurements do not reveal where the ancient gases come from. 鈥淏ut 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,鈥� says Caffee. 快猫短视频s will have
to rethink gaseous exchange between the Earth and atmosphere, he says.
