Chondrite water content

Murchison (meteorite) A carbonaceous chondrite, type II (CM2), suspected to be of cometary origin due to its high water content (12 percent)... 

The Cl chondrites represent one of the most curious paradoxes of cosmochemistry. Despite their unfractionated compositions, the Cl chondrites are the most altered of all chondrites, with water contents of —19.5 wt.% (Nagy et al., 1963). Anhydrous phases (olivines and pyroxenes) represent less than 1 vol.% of these meteorites (Leshin et al., 1997). Cl chondrites are complex meteorites that consist of a dark, fine-grained matrix comprised of phyllosilicates with magnetite, sulfides, carbonates, and sulfates embedded within it (e.g., DuFresne and Anders, 1962 Nagy, 1966). They have experienced extensive breccia-tion on their asteroidal parent bodies that caused... 

Water cycling in the Archaean More difficult to predict is how water was distributed in the Archaean mantle. It will be shown later (see Section 5.2) that the Earth was initially volatile-rich, when it accreted and it subsequently lost water and other volatiles. Indicative here is the comparison between the water content of carbonaceous chondrites, the likely primitive material of Earth accretion (up to ca. 10 wt%), and the estimated water content of the present-day silicate Earth and hydrosphere (0.19-0.24 wt%, see Table 5.2). 

As we have mentioned in the chapter about meteorites, chondrites are the most primitive meteorite class. Hydrogen and oxygen are present mainly in the form of OH, the water content in the achondrites is lower (up to 3%). The degassing during accretion leads to a wide range of the mass of their possible atmospheres from less than 1% of the planet s total mass to 6% by mass of hydrogen, 20% of water and 5% of carbon compounds. Planets with deep surface liquid water oceans could have formed after the accretion has stopped. 

Robert F, Epstein S (1982) The concentration and isotopic composition of hydrogen, carbon and nitrogen carbonaceous meteorites. Geochim Cosmochim Acta 46 81-95 Robert F, Merlivat L, Javoy M (1978) Water and deuterium content in ordinary chondrites. Mete-oritics 12 349-354... 

Bulk hydrogen and 36Ar contents versus mineral alteration index for CM carbonaceous chondrites. These trends reflect progressive incorporation of water and destruction of the noble gas carrier as alteration advances. After Browning et al. (1996). 

Ashworth, and Hutchison, 1975 [11] made electron microscopic observations of the hydrous alteration products of olivine in an achondrite and in an ordinary chondrite. Their conclusion was that the Nakhla achondrite, and possibly the Weston chondrite, contain water of extraterrestrial origin which was mobilized by mild shock deformation. Carbonaceous chondrites are believed to be unaltered material left over from the formation of the solar system. They contain substantial amounts of reduced carbon and of water in the form of hydroxyl ions. The oxidation state of iron in some carbonaceous chondrites has been determined by means of Moess-bauer spectroscopy, and it is demonstrated that there is a correlation between the oxidation state of iron and the content of water and reduced carbon in the meteorites (Roy-Poulsen et al., 1981 [284]). 

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