Analyses of noble gases hint that air didn't fizz from within the planet
Isotopic analyses of the gases krypton and xenon suggest that much of Earth’s atmosphere came from outer space, not inner space.
Krypton and xenon appear in Earth’s atmosphere — and in the universe as a whole — only in trace amounts. Detailed analyses of the gases provide clues about where those atmospheric components originated, says Greg Holland, an isotope geochemist at the University of Manchester in England. Those analyses, reported in the Dec. 11 Science, suggest that those gases, as well as many others now cloaking our planet, arrived via comets or were swept up from nearby gas clouds during the late stages of Earth’s formation.
Some scientists have proposed that the gases in Earth’s atmosphere originated within the planet, says Holland. According to those arguments, the atmosphere either seeped out of the Earth as the planet gradually cooled or were expelled from the crust when large numbers of asteroids pummeled