Comets from outer space may have created Earth鈥檚 atmosphere 鈥� not volcanoes spewing out gases from deep within the planet.
The origin of the gases in Earth鈥檚 atmosphere has long been a puzzle. One of the main theories is that the gases bubbled up out of the mantle via volcanoes.
of the University of Manchester, UK, and colleagues have arrived at a different theory after collecting samples of the noble gas krypton from several hundred metres beneath New Mexico.
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They found that the mantle鈥檚 chemical fingerprint was rich in 鈥渉eavy鈥� isotopes of krypton such as krypton-86 and krypton-84, and poorer in 鈥渓ighter鈥� forms such as krypton-82. This is a composition that closely resembles meteorites 鈥�- support for the ideas that gas-rich meteorites colliding in the early solar system formed our planet.
鈥淭he results confirm one of the basic ideas of planetary formation theory, that most of the Earth formed by collisions of smaller objects like carbonaceous chondrites,鈥� says at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts.
Light atmosphere
But where did the atmosphere come from 鈥�- it is rich in lighter isotopes so the mantle cannot be the source, says Holland. Earth鈥檚 atmosphere cannot have gained a greater proportion of lighter isotopes since it formed. Because light isotopes of krypton escape into space more quickly than heavy isotopes, the atmosphere can only get 鈥渉eavier鈥�
If not the mantle then what? , a co-author and colleague of Holland鈥檚 suggests that comets could be the answer. At the outer edges of the solar system, in the Kuiper Belt, are millions of icy bodies that formed when the solar system was born. These comets have noble gas signatures that resemble that of our modern atmosphere.
A shift in Jupiter鈥檚 orbit around 4.5 billion years ago may have jarred the Kuiper Belt, flinging icy comets at the Earth. 鈥淎ncient Earth was strewn with huge volcanoes spewing out gas, but our research shows that the real source of Earth鈥檚 first atmosphere was actually outer space,鈥� says Ballentine, a co-author of the paper and colleague of Holland鈥檚.
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