Researchers from the United States, Great Britain, and Denmark analyzed the composition of marine sedimentary rocks from South Africa, which date back to the Paleoproterozoic period – from 2.5 to 1.6 billion years ago.
The results of a new study by an international group of scientists say that oxygen appeared in the Earth’s atmosphere 2.22 billion years ago, that is, 200 million years later than previously thought.
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Using the isotopic signatures of sulfur, iron, and carbon, scientists have reconstructed a detailed picture of changes in the redox environment in the ocean during the Paleoproterozoic.
Initial oxygen enrichment, up to about ten to five from the one recorded in the atmosphere now, has passed about two and a half billion years. But all this time the oxygen level was falling and rising, and 2.22 billion years ago became a permanent part of the Earth’s atmosphere.
This explains the sharp climatic changes, in particular, the four global glaciations.
“The ratios of atmospheric gases: oxygen, methane and carbon dioxide provoked a sharp cold snap. Perhaps the main sources of greenhouse gases were volcanoes, because periods of warming are associated with active phases of volcanism. When volcanoes subsided, glaciation occurred again,” the study says.
The second increase in the oxygen content in the Earth’s atmosphere occurred during the transition of the Proterozoic to the Cambrian period and created conditions for the development of complex forms of living organisms.
It was previously reported that Mars possessed an oxygen atmosphere about four billion years ago, long before the Earth’s air shell was enriched with oxygen, which occurred about 2.5 billion years ago.