Early degassing

Azbel IY, Tolstikhin IN (1993) Accretion and early degassing of the Earth Constraints from PU-U-I-XE isotopic systematics. Meteoritics 28 609-621... 

Fanale, F. P. (1971) A case for catastrophic early degassing of the Earth. Chem. Geol., 8, 79-105. 

Tolstikhin, I. N., O Nions, R. K. (1994) The Earth s missing xenon A combination of early degassing and of rare gas loss from the atmosphere. Chem. Geol., 115, 1-6. 

At the same time, the conclusion concerning the catastrophic early degassing of the Earth and early formation of an ocean whose volume was still limited in the Early Precambrian, can hardly be extended automatically to other volatiles, in particular CO2, sulfur, and probably, HCl. 

Honda M. and McDougall I. (1998) Primordial hehum and neon in the Earth—a speculation on early degassing. Geophys. Res. Lett. 25, 1951-1954. 

Honda, M, McDougall, 1.1997. Primordial helium and neon in the Earth a speculation on early degassing. Seventh Annual Goldschmidt Conference. Lunar and Planetary Institute Contribution, 921, 98-99. 

Xenon isotopes in oceanic basalts provide the most basic evidence on early differentiation of our planet and on formation of the atmosphere. Several Xe isotopes are produced by extinct radioactivity, providing a method to quantify events at the very start of Earth history near 4500 million years ago to a high precision, within several tens of millions of years. The difference between Xe/ °Xe of the mantle and atmosphere is fundamental evidence for their early separation (e.g., Thompson 1980 Staudacher and Allegre 1982). It is thought that formation of the atmosphere involved some early degassing of the mantle. Whether the Earth ever had a primary atmosphere is still an open question, and ultimately depends upon whether the inner planets formed in the presence of a solar nebula gas phase. The timing of these early events, the degree to which Xe isotope differences reflect variations in I/Xe and Pu/Xe of source reservoirs, and the... 

Regarding mantle models, Ne isotopes provide an important constraint on the relationship between mantle and atmospheric gases in models for the mantle distribution and degassing of Ne. The high mantle °Ne/ Ne ratio indicates that simple degassing of the mantle cannot account for a dominant component of the atmosphere (see Marty and Alle 1994). This indicates that either (a) the atmosphere is derived from a different reservoir (which is no longer represented by Ne in the mantle) or (b) Ne in the atmosphere has been altered. The latter could have been caused by hydrodynamic escape to space, with preferential loss of Ne over Ne. Because the conditions necessary for this process could have been present only early in Earth history (Pepin 1991), it therefore requires early degassing of Ne. 

If isotopic fractionation of nonradiogenic Xe occurred during losses from the atmosphere to space, then degassing of nonradiogenic isotopes occurred early while this was still possible (see Pepin 1991). The early degassing of Xe corresponds to the similar requirement for Ne to account for the differences between mantle and atmospheric °Ne/ Ne. In contrast, atmospheric fissiogenic Xe does not appear to be fractionated. 

The very radiogenic Ar and Xe isotope ratios of the upper mantle demand early degassing of the mantle. This is a model-dependent conclusion based on the assumption that upper mantle noble gases are residual from atmosphere degassing. However, Xe isotope systematics precludes such a relationship (Ozima et al. 1985). Since other models, while not necessarily correct, can account for the observed Xe isotope variations, it is clear that the isotopic evidence can be interpreted in various ways. Nonetheless, early transfer of volatiles to the atmosphere probably did occur and was caused by impact degassing. 

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