Free Oxygen in the Late Archean

A study on selenium (Se) isotopes in Australia’s Mount McRae Shale supports the theory that oxygenic photosynthesis originated long before the Great Oxidation Event (GOE), which occurred around 2.3 billion years ago. The Mount McRae Shale is a 2.5 billion-year-old formation and holds a record of enrichment and abundance of Se isotopes. The formation provides a means of studying levels of oxygen in both the ocean and atmosphere over Earth’s history, and indicates that there was a ‘whiff of oxygen’ in the atmosphere prior to the GOE.

The study, “Selenium isotopes support free O2 in the latest Archean,” was published in the journal Geology. Samples for the study came from a 100 meter section of the ABDP-9 drill core, drilled by the NASA Astrobiology Drilling Program in 2004.