New work from University of Washington astrobiologists describes evidence that there was life on land as early as 2.7 billion years ago, and it was affecting global biogeochemical cycles. Microbes were helping to weather land surfaces and release sulfur, facilitating its flow from land into the oceans—which in turn may have helped the spread of life in the oceans.

The models the team used show that in order to produce sufficiently rapid weathering chemistry, photosynthetic microbes in proximity to the land surfaces would have to have been releasing oxygen—even though oxygen levels in the global atmosphere were negligible at the time. This work bolsters evidence that oxygenic photosynthesis as a biological pathway evolved long before the Great Oxidation event in Earth’s history, 2.4 billion years ago.

The paper appears in Nature Geoscience, and is funded in part by NASA’s Astrobiology Institute and Exobiology and Evolutionary Biology Program.