Dolomite, CaMg(CO3)2, is found in much greater abundance in ancient rocks than in modern ones, but why this is true has been one of geology's enduring mysteries. Part of this uncertainty has stemmed from the inability until recently to precipitate dolomite in the laboratory at the low temperatures that must have prevailed at ancient sites of dolomite formation. Fortunately, dolomite does form in some modern environments and, taking clues from them, researchers have discovered that sulfate-reducing bacteria may be the missing ingredient.
Warthmann et al. have cultured a single strain of sulfate-reducing bacteria and shown that when they are grown in conditions like those in which they are found naturally, with sufficient amounts of Ca, Mg and carbonate, dolomite formation occurs within 30 days at a temperature of 30°C. Anaerobic bacteria such as these could have played an important role in dolomitization in Earth's early history, when a more reducing atmosphere existed. -- HJS
Geology 28, 1091 (2000).
