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Incorporation of Solar Noble Gases from a Nebula-Derived Atmosphere During Magma Ocean CoolingThe presence of solar noble gases in the deep interior of the Earth is inferred from the Ne isotopic compositions of MORB (Mid-ocean Ridge Basalts) and OIB (Oceanic Island Basalt); Ar data may also consistent with a solar component in the deep mantle. Models of the transport and distribution of noble gases in the earth's mantle allow for the presence of solar Ar/Ne and Xe/Ne ratios and permit the calculation of lower mantle noble gas concentrations. These mantle data and models also indicate that the Earth suffered early (0.7 to 2 x 10(exp 8) yr) and large (greater than 99 percent) losses of noble gases from the interior, a result previously concluded for atmospheric Xe. We have pursued the suggestion that solar noble gases were incorporated in the forming Earth from a massive, nebula-derived atmosphere which promoted large-scale melting, so that gases from this atmosphere dissolved in the magma ocean and were mixed downward. Models of a primitive atmosphere captured from the solar nebula and supported by accretion luminosity indicate that pressures at the Earth's surface were adequate (and largely more than the required 100 Atm) to dissolve sufficient gases. We have calculated the coupled evolution of the magma ocean and the overlying atmosphere under conditions corresponding to the cessation (or severe attenuation) of the sustaining accretion luminosity, prior to the complete removal of the solar nebula. Such a condition was likely to obtain, for instance, when most of the unaccumulated mass resided in large bodies which were only sporadically accreted. The luminosity supporting the atmosphere is then that provided by the cooling Earth, consideration of which sets a lower limit to the time required to solidify the mantle and terminate the incorporation of atmospheric gases within it. In our initial calculations, we have fixed the nebula temperature at To = 300K, a value likely to be appropriate for nebular temperatures at lAU in the early planet-building epoch. We treated the background (nebula) pressure as an adjustable, time-dependent parameter. Additional information is contained within the original extended abstract.
Document ID
20020073507
Acquisition Source
Ames Research Center
Document Type
Conference Paper
Authors
Woolum, D. S.
(NASA Ames Research Center Moffett Field, CA United States)
Cassen, P.
(NASA Ames Research Center Moffett Field, CA United States)
Wasserburg, G. J.
(California Inst. of Tech. Pasadena, CA United States)
Porcelli, D.
(California Inst. of Tech. Pasadena, CA United States)
DeVincenzi, Donald
Date Acquired
August 20, 2013
Publication Date
January 1, 1998
Subject Category
Geosciences (General)
Meeting Information
Meeting: Origin of the Earth and Moon Conference
Location: Monterey, CA
Country: United States
Start Date: December 1, 1998
End Date: December 3, 1998
Distribution Limits
Public
Copyright
Other

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