Early Earth had a hazy, methane-filled atmosphere

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Early Earth had a hazy, methane-filled atmosphere
A new research paper describes a period more than 2.4 billion years ago, when Earth's atmosphere was filled with a thick, methane-rich haze much like Saturn's moon Titan, seen here in an image taken by NASA's Cassini spacecraft in 2013.

More than 2.4 billion years ago, Earth’s atmosphere was inhospitable, filled with toxic gases that drove wildly fluctuating surface temperatures.

Understanding how today’s world of mild climates and breathable air took shape is a fundamental question in Earth science.

New research suggests that long ago, Earth’s atmosphere spent about a million years filled with a methane-rich haze.

This haze drove a large amount of hydrogen out of the atmosphere, clearing the way for massive amounts of oxygen to fill the air. This transformation resulted in an atmosphere much like the one that sustains life on Earth today.

The group’s results, published March 13, 2017 in the early online edition of the Proceedings of the National Academy of Sciences, propose a new contributing cause for the Great Oxidation Event, which occurred 2.4 billion years ago, when oxygen concentrations in the Earth’s atmosphere increased more than 10,000 times.

“The transformation of Earth’s air from a toxic mix to a more welcoming, oxygen-rich atmosphere happened in a geological instant,” said James Farquhar, a professor of geology at UMD and a co-author of the study.

“With this study, we finally have the first complete picture of how methane haze made this happen.”

“High methane levels meant that more hydrogen, the main gas preventing the build up of oxygen, could escape into outer space, paving the way for global oxygenation,” said Aubrey Zerkle, a biogeochemist at the University of St. Andrews and a co-author of the study.

“Our new dataset constitutes the highest resolution record of Archean atmospheric chemistry ever produced, and paints a dramatic picture of Earth surface conditions before the oxygenation of our planet.”

The methane haze persisted for about a million years. After enough hydrogen left the atmosphere, the right chemical conditions took over and the oxygen boom got underway, enabling the evolution of all multicellular life.

The key to the researchers’ analysis was the discovery of anomalous patterns of sulfur isotopes in the geochemical records from this time.

Sulfur isotopes are often used as a proxy to reconstruct ancient atmospheric conditions, but previous investigations into the time period in question had not revealed anything too unusual.

“Reconstructing the evolution of atmospheric chemistry has long been the focus of geochemical research,” said Gareth Izon, lead author of the study.

“Our new data show that the chemical composition of the atmosphere was dynamic and, at least in the prelude to the Great Oxidation Event, hypersensitive to biological regulation.”

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News source: University Of Maryland. The content is edited for length and style purposes.
Figure legend: This Knowridge.com image is credited to NASA/JPL-Caltech/Space Science Institute.