In a new study led by the University of Leeds, scientists have found out when oxygen appeared in the Earth’s atmosphere.
It is believed that the Earth’s atmosphere was initially white anoxic, and about 2.43–2.45 billion years ago, it was significantly enriched with oxygen.
To clarify these data, researchers from the United States, Great Britain, and Denmark analyzed the composition of marine sedimentary rocks from South Africa, dating from the age of their formation to the Paleoproterozoic – from 2.5 to 1.6 billion years.
They then reconstructed the changes in redox conditions in the ocean from that period using the isotopic signatures of sulfur, iron, and carbon to determine oxygen levels in the ancient atmosphere.
It turned out that the initial oxygen enrichment occurred about 2.43 billion years ago. Then, O2 levels fell and rose again and again before becoming a permanent component of the Earth’s atmosphere about 2.22 billion years ago.
These findings help explain four widespread glaciations that occurred concurrently with the Great Oxidation Event, some of which likely covered the entire Earth with ice over millions of years.