Prebiotic carbon in clays from Orgueil and Ivuna (CI), and Tagish Lake (C2 ungrouped) meteorites

Abstract

Transmission electron microscopic (TEM) and electron energy-loss spectroscopic (EELS) study of the Ivuna and Orgueil (CI), and Tagish Lake (C2 ungrouped) carbonaceous chondrite meteorites shows two types of C-clay assemblages. The first is coarser-grained (to 1 micrometer) clay flakes that show an intense O K edge from the silicate together with a prominent degrees C K edge, but without discrete degrees C particles. Nitrogen is common in some clay flakes. Individual Orgueil and Tagish Lake meteorite clay flakes contain up to 6 and 8 at% degrees C, respectively. The degrees C K-edge spectra from the clays show fine structure revealing aromatic, aliphatic, carboxylic, and carbonate degrees C. The EELS data shows that this degrees C is intercalated with the clay flakes. The second C-clay association occurs as poorly crystalline to amorphous material occurring as nanometer aggregates of degrees C, clay, and Fe-O-rich material. Some aggregates are dominated by carbonaceous particles that are structurally and chemically similar to the acid insoluble organic matter. The degrees C K-edge shape from this degrees C resembles that of amorphous degrees C, but lacking the distinct peaks corresponding to aliphatic, carboxylic, and carbonate degrees C groups. Nanodiamonds are locally abundant in some carbonaceous particles. The abundance of degrees C in the clays suggest that molecular speciation in the carbonaceous chondrites is partly determined by the effects of aqueous processing on the meteorite parent bodies, and that clays played an important role. This intricate C-clay association lends credence to the proposal that minerals were important in the prebiotic chemical evolution of the early solar system.