Early chemical history of the solar system

Abstract

The extreme antiquity and lack of evidence for significant chemical processing of the chondritic meteorites since they were formed suggest the possibility that their chemistry and mineralogy may have been established during the condensation of the solar system. By using equilibrium thermodynamics, the sequence of condensation of mineral phases from a cooling nebula of solar composition has been calculated. Applying the predictions of these theoretical models suggests that (1) the chemistry and mineralogy of Ca‐Al‐rich inclusions in C2 and C3 chondrites were established during condensation at temperatures >1300°K; (2) fractionation of such inclusions is necessary to account for the refractory element depletions of ordinary and enstatite chondrites relative to the carbonaceous chondrites; (3) the metal‐silicate fractionation in ordinary chondrites took place in the nebula at T < 1000°K and Ptot ∼ 10−5 atm; (4) the volatile element depletion of C2 and C3 chondrites relative to C1 chondrites took place during chondrule formation; (5) the most volatile elements are depleted in ordinary chondrites because they accreted before these elements were totally condensed; and (6) many chemical features of planetary rare gases and organic material in carbonaceous chondrites could have been established during condensation. Chemical fractionation during condensation may also be responsible for the heterogeneous accumulation of the earth, the refractory element enrichment of the moon, and the varying Fe/Si ratios of the terrestrial planets.

Potassium isotope cosmochemistry: Genetic implications of volatile element depletion

“…This can be extended to any model using chondrites or chondritic components as the building blocks of the terrestrial planets. It is suggested that condensation from a hot solar nebula as envisaged by Grossman and Larimer ( 1974) qualitatively accounts for the volatile depletion observed in the components of meteorites and planets. A plausible nebular thermal structure has been found by Boss ( 1993), who included compressional heating of the infalling gas, and obtained temperatures sufficient to completely devolatilize any presolar grains.…”

“…The result of this experiment is that there are no detectable isotopic fractionations of K isotopes during a process of volatile element fractionation that produced a factor of 30 loss of potassium (Cl chondrites to the Moon). The simple conclusion is that volatile element depletion is not the effect of vaporization of condensed material, but that the chemical fractionations were produced during condensation, such as may have taken place from a hot solar nebula (Grossman and Larimer, 1974).…”

“…He further concluded that " (t)his mixing is the most important single thing to be said about isotopes." It has been construed as evidence for a high temperature event in the inner solar system that eradicated all presolar records (Suess, 1965;Podosek, 1978), and taken to imply that the chemical evolution of material ending up in the chondrites was controlled by the cooling of a gas of solar composition from a temperature well above that required to vaporize all initial dust F= 2000 K (Larimer and Anders, 1970;Grossman and Larimer, 1974). Calculations of the collapse of a molecular cloud core have provided evidence both for and against an initially hot solar nebula depending on the physics used and the boundary conditions assumed (Ruden and Lin, 1986;Cameron, 1988;Boss, 1993).…”

“…Two kinds of mechanism can be proposed to account for the chemical fractionations observed in chondrites and planets: those involving incomplete condensation of volatiles, e.g., from a hot nebula (Larimer and Anders, 1967;Grossman and Larimer, 1974) and those involving the evaporation of Cllike matter accreted from a cold solar nebula (Ringwood, 1966). The mechanism of volatile element depletion holds the key to whether planetary and chondritic material formed from a hot solar nebula or a cold nebula, and is, therefore, an independent constraint on models of the thermal structure of the nebula derived from calculations of protostellar origin (Ruden and Lin, 1986;Cameron, 1988;Boss, 1993).…”

Infrared spectroscopy of asymptotic giant branch stars in the Galactic bulge

“…Theoretical studies on dust formation have a long history in astrophysics dating back to Salpeter (1974) for stellar ejecta and Grossman & Larimer (1974) for the solar nebula. These and subsequent studies (Sedlmayr 1989;Kozasa & Sogawa 1997) rely on thermodynamic condensation sequences to predict the compounds formed and the fraction of mass locked up in them.…”