The oxygenation of Earth's atmosphere to support life happened 3.8 billion years ago -- some 0.7-0.8 billion years earlier than previously thought, scientists report.
Researchers across the world agree that oxygenation happened in two major steps: the first during the so-called "Great Oxidation" Event about 2.5-2.4 billion years ago and the second during the Late Neoproterozoic Era around 750 to 540 million years ago.
The latter is thought to have been the cause for the emergence of animals during the so-called "Cambrian explosion" nearly 540-520 million years ago.
The discovery opens up for the possibility of evolution of the earliest primitive photosynthetic life forms as early as 3.8 billion years ago.
"It is generally believed that early Earth was completely anoxic (without oxygen) but our study shows that the surface of the Earth was exposed to a low oxygen atmosphere already by this time," explained lead researcher Robert Frei from University of Copenhagen.
To reach this conclusion, the researchers analysed Earth's oldest banded iron formations (BIFs) from Western Greenland.
BIFs are marine chemical sediments and retain information on the composition and presence of oxygenation/reduction processes in ambient seawater and on the interaction of the atmosphere with Earth's surface.
The analyses of the BIF layers from Western Greenland show elements that require presence of oxygen in the atmosphere.
"This has far reaching implications for how we investigate the pace of evolution of life and its biodiversity on our planet," the authors noted in a paper published in Nature's Scientific Reports.
