Assaying Ancient Bacteria

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Science  11 Aug 2000:
Vol. 289, Issue 5481, pp. 835
DOI: 10.1126/science.289.5481.835b

The Precambrian fossil record extends back to about 3.5 billion years ago, and chemical evidence for the possible appearance of life extends several hundred million years earlier. Determining the evolution of metabolic pathways of bacteria is important for inferring how bacteria may have influenced the chemistry of rocks and Earth's atmosphere. Some information has been obtained from isotopic studies because metabolic pathways can produce distinct isotopic signatures; but these have required large samples and it often was unclear if the analyses represented a specific organism.

House et al. used the ion microprobe to conduct carbon isotopic analyses of some individual Precambrian microfossils. Analysis from fossils as old as 2.1 billion years ago are consistent with carbon fixation by two processes—the Calvin cycle and the acetyl-CoA pathway—and establishes the presence of cyanobacteria. Rasmussen and Buick used carbon isotopes to show that there was enough organic material produced by marine biota about 3.2 billion years ago to generate significant amounts of petroleum. — BH

Geology28, 707 (2000); Geology28, 731 (2000).

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