From “Salty Water and Gas Sucked Into Earth’s Interior Helps Unravel Planetary Evolution” (ScienceDaily Sep. 26, 2011), we learn:
Lead author Dr Mark Kendrick from the University of Melbourne’s School of Earth Sciences said inert gases trapped inside Earth’s interior provide important clues into the processes responsible for the birth of our planet and the subsequent evolution of its oceans and atmosphere.
“Our findings throw into uncertainty a recent conclusion that gases throughout the Earth were solely delivered by meteorites crashing into the planet,” he said.
It’s a lot to ask of the meteorites …
Because the composition of neon in Earth’s mantle is very similar to that in meteorites, it was recently suggested by scientists that most of Earth’s gases were delivered by meteorites during a late meteorite bombardment that also generated visible craters on Earth’s moon.
“Our study suggests a more complex history in which gases were also dissolved into the Earth while it was still covered by a molten layer, during the birth of the solar system,” he said.
These days, go for the more complex history.