New Clues To Oxygen At The Origin Of The Solar System
ScienceDaily (Sep. 17, 2008) — Oxygen is the most abundant element on Earth, accounting for almost half the planet’s mass. Of its three stable isotopes, oxygen 16 (16O, whose nucleus contains eight neutrons) makes up 99.762 percent of oxygen on Earth, while heavier oxygen 17 (17O, with nine neutrons) accounts for just 0.038 percent, and the heaviest isotope, oxygen 18 (18O, with 10 neutrons), makes up 0.2 percent.
Yet minerals in some of the most primitive objects in the solar system, including the meteorites called carbonaceous chondrites, have quite different ratios of oxygen isotopes than on Earth; presumably the rare heavy isotopes occurred in much greater abundances in the early solar system.
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