Geology

Holes in Rocks

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Science  12 Jun 2009:
Vol. 324, Issue 5933, pp. 1367
DOI: 10.1126/science.324_1367a
CREDIT: UNIVERSITY OF WASHINGTON

Most minerals in Earth's crust are built on a Si–O(2−)–Si framework. Commonly, these minerals contain minor O()–O() dimers as impurities distributed throughout the bulk of the crystal. When minerals within rocks experience mechanical stress, the weak bonds holding the dimers together are broken, creating a charge imbalance that gives rise to mobile positive holes. These holes travel through stressed mineral grains to other nearby minerals—like current passing through a p-doped semiconductor—until they eventually arrive at the rock's surface. Through a series of electrochemical experiments, Balk et al. demonstrate that such holes at the surface of rocks in simulated seawater rapidly oxidize water to form H2O2. Because crustal rocks are predominately in contact with water and are almost always experiencing some type of stress from processes such as plate tectonics, glacial movement, and lithostatic pressuring, the oxidation of water by stressed minerals might have helped to contribute oxygen to Earth's early atmosphere. Conceivably, H2O2 generated at rock-water interfaces could also have provided evolutionary pressure for local organisms to develop survival mechanisms in highly oxidizing microenvironments.

Earth Planet. Sci. Lett. 283, 87 (2009).

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