Rock Cake for Bugs

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Science  11 May 2001:
Vol. 292, Issue 5519, pp. 1017
DOI: 10.1126/science.292.5519.1017g

The New Albany Shale is a remnant of Late Devonian mud that is rich in carbon in the forms of natural gas and resistant organic matter, or kerogen. When such sedimentary rocks are exposed, the carbonaceous material is weathered by several chemical and physical processes. Petsch et al. (p. 1127) now show that bacteria also process kerogen. They have isolated microorganisms from cores and monitored their consumption of kerogen in powdered, sterilized rock by measuring the incorporation of 14C versus 13C isotopes (14C is absent in ancient organic matter). At least three-quarters of the carbon assimilated by their bacterial cultures originated from the rock. Until now, kerogen was not thought to be bioavailable, but this work shows that bacterial consumption of organically rich sediments may be a significant factor in weathering and, over geological time scales, may have made a significant contribution to global biogeochemical carbon cycles.

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