Geochemistry

Eating Their Crusts

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Science  08 Sep 2000:
Vol. 289, Issue 5485, pp. 1653
DOI: 10.1126/science.289.5485.1653b

Seawater circulates through new oceanic crust formed at mid-ocean ridges, and the subsequent reactions can add or remove elements from the oceans. Bacteria may also mitigate crustal alteration at low temperatures (<120°C)— microscopic observations have revealed small, micrometer-sized channels or tubes extending into rocks at the alteration front even deep in the crust, as well as the nearby presence of organic matter and DNA.

A detailed examination of an alteration front by Alt et al. with transmission electron microscopy now reveals that many of the small tubes are mostly filled with clay minerals produced by the divitrification of the volcanic basaltic glass (an ion exchange process in which potassium is leached from seawater). Thus, the available room in many tubes would seem to present a tight squeeze for most bacteria. In addition, the amount of potassium consumed would have required the circulation of large volumes of seawater. — BH

Earth Planet Sci. Lett.181, 301 (2000).

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