Oxygen had to fight for 'war' for Earth's atmosphere

Earth's oxygen levels rose and fell more than half a million years before the planet-wide success of the Great Oxidation Event about 2.4 billion years ago, according to new research.

The evidence comes from a new study that A distant past in the atmosphere and on the surface of a large stretch of ocean-showing that the oxygenation of the earth is a complex process

"These transient oxygenation events have been battles in the war, when the balance tipped more in favor of oxygenation."

The finding also may have implications in the search for life beyond Earth. Coming years will bring powerful new ground- and space-based telescopes able to badyze the atmospheres of distant planets. This work could help keep astronomers from unduly ruling out "false negatives," or "uninitiated planets that may not be at first appear to be undetectable oxygen levels."

"The production and destruction of oxygen in the ocean and atmosphere over time "says Matt Koehler, a doctoral student in earth and space sciences at the University of Washington and a lead author of the new paper in the Proceedings of the National Academy of Sciences .

"These transient oxygenation events were battles in the war, when the balance tipped more in favor of oxygenation."

In 2007, coauthor Roger Buick, professor of earth and space sciences, was part of a team of scientists that found evidence of an episode-a "whiff" -of oxygen to 50 million to 100 million years before the Great Oxidation Event. They learned this by drilling deep into sedimentary rocks of the Mount McRae Shale in Western Australia and badyzing the samples for the trace metals molybdenum and rhenium,

In the past, about 150 million years ago-about 2.66 billion years ago-and lasting for less than 50 million years. For this work they are used for different types of oxygen-nitrogen isotopes and the element selenium-substances that, each in its way, also tell of the presence of oxygen.

"What we have in this paper is another detection, at high resolution, of a transient whiff of oxygen, "says Koehler. "Nitrogen isotopes tell a story about oxygenation of the ocean surface, and this oxygenation spans over 50 million years."

Rock layers

Buick in 2012 at another site in the northwestern part of Western Australia called the Jeerinah Formation.

The researchers drilled two cores about 300 kilometers (about 186 miles) away from the sedimentary rocks-one core sediment samples deposited in shallower waters, and the other samples sediments from deeper waters. Buick says, "stepwise" changes in nitrogen isotopes "and then back again to zero. This can only be considered as oxygen in the environment. It's really cool-and it's sudden. "

The nitrogen isotopes reveal the activity of certain marine microorganisms that use oxygen to form nitrates, and other microorganisms that use this nitrate for energy. The data collected from the ocean isotopes the surface of the ocean, while selenium suggests oxygen in the air of ancient Earth. Koehler says the deep ocean was likely anoxic, or without oxygen, at the time

How to hotter early Earth became the rocky planet it is today

from the nearby land, not making it to deeper water. Selenium is held in sulfur minerals on land; Higher atmospheric oxygen would be more likely to be leached by oxidative weathering- "the rusting of rocks," Buick says-and-transported to sea.

"That selenium then accumulates in ocean sediments," Koehler says. "

Exoplanets, too

The finding, Buick and Koehler say, also has relevance for life detecting Exoplanets, or those beyond the solar system.

"One of the strongest atmospheric biosignatures is thought to be oxygen, but this study confirms that during a planet's transition to oxygen, A few million years ago and then slip back into anoxia, "Buick says.

" So, if you fail to detect oxygen in a planet's atmosphere, that does not mean that the planet is uninhabited or even that it lacks photosynthetic life. Merely that it has not built up enough sources of oxygen

"In other words, lack of oxygen can easily be a false negative for life." 19659015] Methane from microbes kept early Earth warm

Koehler adds: "

Koehler's other coauthors are from the University of Washington, University of St. Andrews in Scotland, and Arizona State University.

Grants from NASA, the UW-based Virtual Planetary Laboratory, and the National Science Foundation funded research. The Agouron Institute funded the drilling

Source: University of Washington