Geochemistry

Elemental Traces

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Science  25 Feb 2005:
Vol. 307, Issue 5713, pp. 1171
DOI: 10.1126/science.307.5713.1171d

Microbes modify soil. What is obvious to most of us is that they process organic matter derived from higher plants and animals. What is less apparent is that they produce organic ligands and acids that bind to elements such as iron and other metals, and this affects their solubility and mobility. Thus, a soil containing microbes has a different inorganic chemistry than one lacking microbes.

The mobility of elements can be used as a measure of leaching and integrated rainfall and also as an indication of microbial activity. Neaman et al. have used elemental mobilities to help ascertain whether microorganisms had managed to invade Earth's land surface in the Archean. For consistency, the authors examined several ancient soils produced on one rock type—basaltic lava flows—and simulated the effects of microorganisms on such a soil in the laboratory. The presence of organic ligands greatly increased the mobility of Fe and P, changing the soil profile. These effects were evident in soils dating to 2.7 billion years ago, implying that at least some microorganisms were a significant presence on Earth's surface then, not just in the oceans. — BH

Geology 33, 117 (2005).

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