Science Daily peeks into the deep, deep history of the “Great Oxidation Event,” analyzing a very old sample of some of the first oxygen to appear on Earth:
Christopher Junium, assistant professor of Earth Sciences, is part of a team of researchers led by Aubrey Zerkle, a biogeochemist at the University of St. Andrews in Scotland, which has uncovered evidence of an interaction between nitrogen and oxygen in ancient rocks from South Africa. The discovery not only illuminates how life evolved alongside changes in the chemistry of the Earth’s surface, but also fills in a 400-million-year gap in geochemical records.
Scientists have long suspected that certain visible signals have accompanied the GOE in geochemical records; however, many of the records are plagued with gaps. “Understanding the nitrogen cycle through the Earth’s history is important because it controls global primary productivity, which, in turn, regulates climate, weathering and the amount of oxygen at the Earth’s surface,” says Junium, a sedimentary and organic geochemist.
Working with cores of sedimentary rock from the South African town of Donkerhoek, Junium and his colleagues used nitrogen stable isotopic analysis to record environmental conditions during the GOE. They found that the first occurrence of widespread nitrate coincided with the initial appearance of oxygen in the atmosphere.
Estimated concentration of oxygen in the Earth’s atmosphere over the Precambrian Era (4.56 to 0.541 billion years). Junium says that, during the GOE, oxygen concentrations in the atmosphere increased by as much as four orders of magnitude, near or above modern levels.
The prevailing notion is that such a confluence of events would have triggered the rapid diversification of complex organisms, ones reliant on atmospheric oxygen. Instead, more than a billion years passed before oxygen levels were high enough for the evolution of complex eukaryotes (i.e., cells or organisms sharing complex structural characteristics) to occur. Why the delay?
“It remains an item of intense interest amongst the geochemical community, a question that we are actively seeking to answer,” Junium adds.