Review

Alkaline fluid circulation in ultramafic rocks and formation of nucleotide constituents: a hypothesis

Nils G Holm , Marion Dumont , Magnus Ivarsson and Cécile Konn

Dept. of Geology and Geochemistry, Stockholm University, Stockholm, Sweden

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Geochemical Transactions 2006, 7:7doi:10.1186/1467-4866-7-7

Published:	25 July 2006

Abstract

Seawater is constantly circulating through oceanic basement as a low-temperature hydrothermal fluid (<150°C). In cases when ultramafic rocks are exposed to the fluids, for instance during the initial phase of subduction, ferromagnesian minerals are altered in contact with the water, leading to high pH and formation of secondary magnesium hydroxide, among other – brucite, that may scavenge borate and phosphate from seawater. The high pH may promote abiotic formation of pentoses, particularly ribose. Pentoses are stabilized by borate, since cyclic pentoses form a less reactive complex with borate. Analyses have shown that borate occupies the 2' and 3' positions of ribose, thus leaving the 5' position available for reactions like phosphorylation. The purine coding elements (adenine, in particular) of RNA may be formed in the same general hydrothermal environments of the seafloor.