Another 100 million years before Earth saw a permanent increase in oxygen

The permanent increase in oxygen in Earth’s atmosphere, which fundamentally changed the subsequent nature of Earth’s habitability, occurred much later than expected, new research shows.

And the study, carried out by an international team led by the University of Leeds and comprising researchers from the University of California-Riverside, Harvard University, the University of Southern Denmark and the University of St Andrews, also provides an explanation for some of the more extreme. climatic episodes affected the Earth, when the planet was repeatedly covered with ice.

The first time that oxygen was significantly present in the atmosphere was around 2.43 billion years ago, and this marks the start of the great oxidation event – a pivotal period in Earth’s history.

Although the great oxidation event led to even much lower oxygen levels than today, it drastically changed the chemical makeup of the planet’s surface and set the stage for the subsequent course of the biological evolution on Earth, which ultimately led to a planet teaming up with animals. life.

By analyzing rocks from South Africa, which were deposited in the ocean at the time of the great oxidation event, the researchers found that the early atmospheric oxygenation was short-lived and the oxygen only became a permanent feature of the atmosphere that much later.

Professor Simon Poulton, School of Earth and Environment, Leeds, led the research.

He said: “The Great Oxidation Event fundamentally changed the Earth’s environment and habitability. This first period of oxygenation was thought to have occurred around 2.43 billion to 2.32 billion ago. years.

“However, our research shows that in fact the oxygenation of the atmosphere was very unstable over a period of about 200 million years, with permanent atmospheric oxygenation occurring about 100 million years later than this. than we thought before. “

Their findings, published in the journal Nature, also suggest a direct link between fluctuations in atmospheric oxygen concentration and greenhouse gas concentrations.

University of California-Riverside Professor Andrey Bekker, co-author of the study, said: “These results help explain four generalized glaciations that occurred concurrently with the great oxidation event, some of which would probably have covered all of Earth in ice for millions of years.

“Our new data shows that the permanent increase in oxygen occurred after the last major ice age of the period and not before it, which was previously a major puzzle in our understanding of the links between atmospheric oxygenation. early and intense climatic instability. “

The research team renamed this period the episode of great oxidation. It ushered in a 1.5 billion year period of subsequent climatic and environmental stability, which continued until a second major period of increased oxygen and climatic instability at the end of the period. Precambrian.

Harvard University co-author Professor David Johnston said: “Increased atmospheric oxygen has been a key factor in the habitability of Earth.

“Unraveling the history of atmospheric oxygenation finally allows us to understand how oxygen reached levels sufficient to allow the evolution of animals.

“The great oxidation episode, when atmospheric oxygen first reached appreciable levels, represents a turning point in this history.

Professor Poulton added: “We cannot begin to understand the causes and consequences of atmospheric oxygenation, the most important control over the habitability of the Earth, if we do not know when permanent atmospheric oxygenation s. ‘is actually produced. Now we finally have this piece of the puzzle. ”