Reviews in Mineralogy & Geochemistry Vol. 75 pp. 575-606, 2013 18 Copyright © Mineralogical Society of America Serpentinization, Carbon, and Deep Life Matthew O. Schrenk, William J. Brazelton Department of Biology East Carolina University Greenville, North Carolina 27858-2502, U.S.A.
[email protected] [email protected] Susan Q. Lang Department of Earth Sciences ETH Zürich 8092 Zürich, Switzerland
[email protected] INTRODUCTION The aqueous alteration of ultramafic rocks through serpentinization liberates mantle carbon and reducing power. Serpentinization occurs in numerous settings on present day Earth, including subduction zones, mid-ocean ridges, and ophiolites and has extended far into Earth’s history, potentially contributing to the origins and early evolution of life. Serpentinization can provide the energy and raw materials to support chemosynthetic microbial communities that may penetrate deep into Earth’s subsurface. Microorganisms may also influence the composition and quantity of carbon-bearing compounds in the deep subsurface. However, conditions created by serpentinization challenge the known limits of microbial physiology in terms of extreme pH, access to electron acceptors, and availability of nutrients. Furthermore, the downward transport of surface carbon and subsequent mixing with calcium-rich fluids at high pH contributes to the precipitation and immobilization of carbonate minerals. The following chapter will explore the physiological challenges presented by the serpentinite environment, data from studies of serpentinite-hosted microbial ecosystems, and areas in need of further investigation. THE PROCESS OF SERPENTINIZATION Physical and chemical consequences of serpentinization Serpentinization is an alteration process of low-silica ultramafic rocks, characteristic of the lower oceanic crust and upper mantle. These rocks are rich in the minerals olivine and pyroxene.