Fossil Stromatolites (IMAGE)

University of Washington

Fossil Stromatolites

Caption

These giant mounds of fossil stromatolites from about 2.5 billion years ago are located in South Africa. For scale, notice a person's dangling legs at the top center. These layered minerals were deposited on an ancient coastline by communities of microbes, including photosynthetic bacteria that generated oxygen. The new study suggests that for millions of years the oxygen produced by these microbes reacted with volcanic gases before it began to accumulate in Earth's atmosphere, about 2.4 billion years ago.

Credit

David Catling/University of Washington

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