Most researchers imagine the initial oxygenation of the ocean and atmosphere to have been something like a staircase, but with steps only going up.
They believe the first step occurred around 2.4 billion years ago, and the so-called Great Oxidation Event, has obvious implications for the origins and evolution of the first forms of eukaryotic life.
The second big step in this assumed irreversible rise occurred almost two billion years later, coinciding with the first appearances and earliest diversification of animals.
Researchers led by geochemists at the University of California, Riverside have now challenged the simple notion.
"Our group is among a subset of scientists who imagine that oxygen, once it began to accumulate in the ocean-atmosphere system, may have ultimately risen to very high levels about 2.3-2.2 billion years ago, perhaps even to concentrations close to what we see today," said Timothy Lyons, principal investigator of the project.
"But unlike the posited irreversible rise favoured by many, our new data point convincingly to an equally impressive, and still not well understood, fall in oxygen about 200 million years later," Lyons said in a statement.
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According to him, this drop in oxygen may have ushered in more than a billion years that were marked by a return to low-oxygen concentrations at Earth's surface, including the likelihood of an oxygen-free deep ocean.
"It is this condition that may have set the environmental stage and ultimately the clock for the advance of eukaryotic organisms and eventually animals," he said.
The research team is thrilled to have found strong chemical evidence for oxygen variability on the early Earth.
"The idea that oxygen levels at Earth's surface went up and down must be vital in any effort to understand the links between environmental and biological evolution on broad, geologic time scales," Noah Planavsky, first author of the study said.
The study results appear in the Proceedings of the National Academy of Sciences.