When scientists reconstruct the early years of the Earth in order to shed light on the emergence and evolution of life, much of this process is influenced by questions of when and to what extent the Earth's atmosphere became oxygenated. Now, new geological studies from the University of Copenhagen show that small levels of atmospheric oxygen were present 3.8 billion years ago, which is approximately 0.7 to 0.8 billion years earlier than previously thought.
Most researchers agree that the oxygenation of Earth's atmosphere occurred over two steps: the first is the Great Oxidation event around 2.5 to 2.4 billion years ago, and the second took place during the Late Neoproterozoic Era around 750 to 540 million years ago. The second event is what most scientists believe to be the cause of the animal emergence approximately 540 to 520 million years ago, also referred to as the "Cambrian explosion."
The new study used data gained from the Earth's oldest Banded Iron Formations (BIFs), which are marine chemical sediments that were originally made up of alternating layers of silica and Fe-hydroxides, that are located in Western Greenland. BIFs are commonly used in geochemical archiving due to their ability to retain information on the composition and presence of oxygenation/reduction processes in ambient seawater as well as the interaction between the Earth's atmosphere and surface.
In the current study, the team analyzed the concentrations and isotope compositions present in the BIFs in order to determine when the continental land masses of western Greenland were exposed to reactive oxygen species (ROS) such as oxygen, with the results revealing that this exposure took place approximately 3.8 billion years ago.
"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, who participated in the research, said in a press release. "This has far reaching implications for how we investigate the pace of evolution of life and its biodiversity on our planet."
The findings were published in the Feb. 11 issue of Scientific Reports.
