Oxygen was present in the atmosphere much earlier than we thought. In a recent study, a team of international researchers examined data from Western Greenland that indicates that small levels of oxygen were already developed in the atmosphere 3.8 billion years ago, which is about 0.7 to 0.8 billion years earlier than previously thought.
"It is generally believed that the Early Earth was a completely anoxic, but our study shows that the surface of the Earth was exposed to a low oxygen atmosphere already this time," Robert Frei, lead author of the study, said in a news release. "This has far reaching implications for how we investigate the pace of evolution of life and its biodiversity on our planet."
The team analyzed some of the Earth's oldest Banded Iron Formations (BIFs) from Western Greenland. BIFs are marine chemicals that were initially composed of layers of silica and Fe-hydroxides. They hold essential information on the presence and composition of oxygenation, and reduction processes in seawater and the atmosphere within the Earth's surface.
The researchers analyzed the concentrations and isotope compositions of chromium (Cr) and uranium (U), which were present in the BIFs. These two elements weathered rapidly when the continental land masses were exposed to reactive oxygen species. After weathering, these elements are dispersed into the ocean, where they are released with chemical sediments and act as geochemical signals of weathering by ROS.
The BIF layers from Western Greenland indicated that the elements required the presence of atmospheric oxygen in order some of the earliest forms of photosynthetic life to develop as early as 3.8 billion years ago.
The findings of this study were published in Scientific Reports.
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