Meteorites volatiles

Pepin, R. O. (1991) On the origin and early evolution of terrestrial planet atmospheres and meteoritic volatiles. Icarus, 92, 2-79. 

The potential components that might have delivered volatile elements to the Earth are the PSN (the major reservoir in the Solar System) and solid matter bodies such as meteorites and comets. The composition of meteoritic volatiles is thought to have been derived from the PSN through elemental and isotopic fractionation. Contributions from sources outside the Solar System such as pre-solar grains or species affected by interstellar chemistry are attested by the discovery of pre-solar grains in primitive meteorites on one hand, and by the large variation of the D/H ratio in the Solar System on another hand, but their extent is a matter of debate. A comparison of the abundances of... 

Palme H, Beer H (1993) Abundances of the elements in the solar system. In Landolt-Bomstein, Group VI Astronomy and Astrophysics, Voigt HH (ed), 3(a). Springer, Berlin, p 196-221 Parker EN (1997) Mass ejection and a brief history of the solar wind. In Cosmic Winds and the Heliosphere. Jokipii JR, Sonett CP, Giampapa MS (eds) Univ Arizona Press, Tucson, p 3-27 Pepin RO (1991) On the origin and early evolution of terrestrial planet atmospheres and meteoritic volatiles. Icarus 92 2-79... 

Pavlov A A, Pavlov AK, Kasting JF (1999) Irradiated interplanetary dust particles as a possible solution for the deuterium/hydrogen paradox of Earth s oceans. J Geophys Res 104 30725-30728 Pepin RO (1989) On the relationship between early solar activity and the evolution of terrestrial planet atmospheres. In The Formation and Evolution of Planetary Systems. Weaver HA, Danly L (eds) Space Tel Sci Inst Symp Series 3, Cambridge University Press, New York p 55-74 Pepin RO (1991) On the origin and early evolution of terrestrial planet atmospheres and meteoritic volatiles. Icams 92 2-79... 

Percentage of meteorites seen to fall. Chondrites. Over 90% of meteorites that are observed to fall out of the sky are classified as chondrites, samples that are distinguished from terrestrial rocks in many ways (3). One of the most fundamental is age. Like most meteorites, chondrites have formation ages close to 4.55 Gyr. Elemental composition is also a property that distinguishes chondrites from all other terrestrial and extraterrestrial samples. Chondrites basically have undifferentiated elemental compositions for most nonvolatile elements and match solar abundances except for moderately volatile elements. The most compositionaHy primitive chondrites are members of the type 1 carbonaceous (Cl) class. The analyses of the small number of existing samples of this rare class most closely match estimates of solar compositions (5) and in fact are primary source solar or cosmic abundances data for the elements that cannot be accurately determined by analysis of lines in the solar spectmm (Table 2). Table 2. Solar System Abundances of the Elements ... 

Chondrite classes are also distinguished by their abundances of both volatile and refractory elements (3). For volatile elements the variation among groups results from incomplete condensation of these elements into soHd grains that accrete to form meteorite parent bodies. Volatile elements such as C,... 

Carbonaceous chondrites (C-chondrites) account for only 2-3% of the meteorites so far found, but the amount of research carried out on them is considerable. C-chondrites contain carbon both in elemental form and as compounds. They are without doubt the oldest relicts of primeval solar matter, which has been changed only slightly or not at all by metamorphosis. C-chondrites contain all the components of the primeval solar nebula, apart from those which are volatile they are often referred to as primitive meteorites . 

The delivery of volatiles to Earth and Mars must have been similar but where has the early Martian atmosphere gone The atmosphere of the inner planets can be seen in Table 7.3. Cometary and meteorite impacts can deliver material to a planet but are also responsible for a process called impact erosion where the atmosphere could be lost due to an impact such as the Earth-Moon capture event. Current estimates suggest that impact erosion may be responsible for the loss of 100 times the current mass of the Martian atmosphere. 

Copper in meteorites is depleted in the heavier 65 isotope with respeet to the Earth (Luek et al. 2003 Russell et al. 2003). Luck et al. s (2003) study of the four main groups of carbonaceous chondrites CI-CM-CO-CV showed that Cu depletion is maximum (-1.5%o) for the C V chondrites (e.g., Allende) for which the depletion of volatile elements is strongest, which indicates that volatilization does not accormt for the observed isotopic heterogeneity (Fig. 4). Luck et al. (2003) found that 8 Cu in CI-CM-CO classes correlates with O excess, but this does not seems to be the case for CV (Luck et al. 2003) nor for the CR, CB, and the particularly Cu-depleted CH-like classes (Russell et al. 2003). In contrast, chondritic Zn is relatively heavy with 8 Zn up to 1 %o (Luck et al. 2001). The rather high 5 Zn values of iron meteorites (up to 4%o)is reminiscent of a similar fractionation of Fe isotopes between metal and silicates (Zhu et al. 2002). 

Figure 4. Correlation between the excesses of of the different classes of meteorites, as measured by their A 0 and their 5 Cu values. The volatile-depleted carbonaceous chondrites (CV) show a deficit in the heavier isotope Cu, which led Luck et al. (2003) to suggest that the observed correlations result from a nucleosynthetic excess of Cu.

In addition to oxygen isotopes, the volatile elements H, C, N, and S also show extremely large variations in isotope composition in meteorites. In recent years, most investigations have concentrated on the analyses of individual components with more and more sophisticated analytical techniques. 

EUer and Kitchen (2004) have re-evaluated the hydrogen isotope composition of water-rich carbonaceous chondrites by stepped-heating analysis of very small amounts of separated water-rich materials. Their special aim has been to deduce the origin of the water with which the meteorites have reacted. They observed a decrease in 5D with increasing extent of aqueous alteration from 0%c (least altered, most volatile rich) to —200%c (most altered, least volatile rich). 

Holloway JR, Blank JG (1994) Application of experimental results to C-O-H species in natural melts. In MR Carroll, JR Holloway (eds.) Volatiles in magmas. Rev Miner 30 187-230 Holser WT (1977) Catastrophic chemical events in the history of the ocean. Nature 267 403 08 Holser WT, Kaplan IR (1966) Isotope geochemistry of sedimentary sulfates. Chem Geol 1 93-135 Holt BD, Engelkemeier AG (1970) Thermal decomposition of barium sulfate to sulfur dioxide for mass spectrometric analysis. Anal Chem 42 1451-1453 Hoppe P, Zinner E (2000) Presolar dust grains from meteorites and their stellar sources. J Geophys Res Space Phys 105 10371-10385... 

By its great mass, the Sun constitutes the major part of the Solar System. In this sense, it is more representative than the planets, which have been the scene of intensive chemical fractionation. The composition of the solar photosphere can thus be compared with the contents of meteorites, stones that fall from the sky, a second source of information on the composition of the protosolar cloud, provided that volatile elements such as hydrogen, helium, carbon, nitrogen, oxygen and neon are excluded. Indeed, the latter cannot be gravitationally bound to such small masses as meteorites and tend to escape into space over the long period since their formation. 

The carbonaceous chondrites, which constitute a tiny proportion of the matter within the Solar System, do conserve within them the original composition of the Solar System. If we exclude the volatile elements mentioned above, these rare meteorites have hardly been affected by the subsequent metamorphism of our planetary system. 

A cosmochemical periodic table, illustrating the behavior of elements in chondritic meteorites. Cosmic abundances are indicated by symbol sizes. Volatilities of elements reflect the temperatures at which 50°/o of each element would condense into a solid phase from a gas of solar composition. As in Figure 1.2, the chemical affinities of each element, lithophile for silicates and oxides, siderophile for metals, and chalcophile for sulfides, are indicated. Some of the most highly volatile phases may have remained uncondensed in the nebula. Stable, radioactive, and radiogenic isotopes used in cosmochemistry are indicated by bold outlines, as in Figure 1.2. Abundances and 50% condensation temperatures are from tabulations by Lodders and Fegley (1998). 

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