Contributions of Icy Planetesimals to the Earth's Early Atmosphere

Laboratory experiments on the trapping of gases by ice forming at low temperatures implicate comets as major carriers of theheavy noble gases to the inner planets. These icy planetesimals may also have brought the nitrogen compounds that ultimately produced atmospheric N2. However, if the sample of three comets analyzed so far is typical, the Earth's oceans cannot have been produced by comets alone, they require an additionalsource of water with low D/H. The highly fractionated neon inthe Earth's atmosphere may also indicate the importance of non-icy carriers of volatiles. The most important additional carrieris probably the rocky material comprising the bulk of the mass of these planets. Venus may require a contribution from icy planetesimals formed at the low temperatures characteristic of the Kuiper Belt.