Geologists revisit the Great Oxygenation Event

Washington University in St. Louis ^ | August 17, 2010 | Diana Lutz

[decimon]

In “The Sign of the Four” Sherlock Holmes tells Watson he has written a monograph on 140 forms of cigar-, cigarette-, and pipe-tobacco, “with colored plates illustrating the difference in the ash." He finds the ash invaluable for the identification of miscreants who happen to smoke during the commission of a crime.

But Sherlock Holmes and his cigarette ash and pipe dottle don’t have a patch on geologists and the “redox proxies” from which they deduce chemical conditions early in Earth's history.

Redox proxies, such as the ratio of chromium isotopes in banded iron formations or the ratio of isotopes in sulfide particles trapped in diamonds, tell geologists indirectly whether the Earth’ s atmosphere and oceans were reducing (inclined to give away electrons to other atoms) or oxidizing (inclined to glom onto them).

It makes all the difference: the bacterium that causes botulism, and the methanogens that make swamp gas are anaerobes, and thrive in reducing conditions. Badgers and butterflies, on the other hand, are aerobes, and require oxygen to keep going.

In the July issue of Nature Geoscience Washington University in St. Louis geochemist David Fike gives an unusually candid account of the difficulties his community faces in correctly interpreting redox proxies, issuing a call for denser sampling and more judicious reading of rock samples.

The world ocean Fike, assistant professor of earth and planetary sciences in Arts & Sciences, focuses on the dramatic change from anoxic to oxygenated conditions in the world’s oceans that preceded the Ediacaran period (from 635 to 542 million years ago) when the first multicellular animals appeared.

[nomorelurker]

off to read some Hal Clement

http://en.wikipedia.org/wiki/The_Nitrogen_Fix

Maybe some Fritz Lieber

http://www.webscription.net/chapters/0743498747/0743498747___6.htm

2nd best survival story ever.

[Lost Dutchman]