Boffins believe it was volcanoes, not just life, that made Earth what it is today – oxygen rich

Photosynthesis alone ain't going to cut it as an explanation

earth_atmosphere

The chemical reaction that produced the outburst of oxygen on Earth was sparked by volcanoes belching carbon dioxide after a major tectonic plate shifted about 2.5 billion years ago, according to the latest research.

A new study published in Nature Geoscience on Monday describes a scenario that could explain two ancient milestones that transformed our planet’s climate into the oxygen-rich habitat we enjoy today: the Great Oxidation Event and the Lomagundi Event.

The first of the two occurred about 2.4 billion years ago, when oxygen was produced for the first time and levels spiked as the gas accumulated in the atmosphere and in the oceans. The second Lomagundi Event began 100 million years after the Great Oxidation Event, and is marked not only by an increase in oxygen but also by a higher than normal abundance of carbon-13 isotopes, compared to its now more common relative carbon-12.

Scientists widely accept the idea that cyanobacteria, single-celled organisms, were the first to pump oxygen into the air as a waste product from photosynthesis. Cyanobacteria absorbed sunlight and carbon dioxide to produce oxygen. But the boost in oxygen from cyanobacteria doesn’t quite match up with the onset of the Great Oxidation Event, according to the paper.

“Most people think the rise of oxygen was linked to cyanobacteria, and they are not wrong,” said James Eguchi, first author of the study and a postdoctoral fellow at the University of California, Riverside.

“The emergence of photosynthetic organisms could release oxygen. But the most important question is whether the timing of that emergence lines up with the timing of the Great Oxidation Event. As it turns out, they do not.”

Cyanobacteria were around 500 million years before the Great Oxidation Event. Although there are many theories that explain why it took awhile for oxygen to build up, none of them also explain the Lomagundi Event.

Instead, there must have been another mechanism that led to the oxygen burst in both the Great Oxidation Event and the Lomagundi Event, the boffins believe. Eguchi and his colleagues think the growth of oxygen was triggered by increased levels of carbon dioxide being spewed by newly formed volcanoes. Here, oxygen can be created by carbon dioxide and water reacting to produce formaldehyde and oxygen.

CO2 + H2O = CH2O + O2

Hundreds of volcanoes sprouted and began emitting higher amounts of carbon dioxide after a massive tectonic shift, the thinking goes. As the temperature warmed, downpours of rain began weathering away minerals in Earth’s rocks and washed them into the ocean.

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These minerals supported a bloom of cyanobacteria and carbonate compounds in the sea. Some of these organic carbon compounds sunk to the bottom of the seafloor and seeped into cracks that exposed the Earth’s mantle.

As they melted in the mantle, the compounds were recycled and released by the volcanoes again. The organic compounds containing carbon-12 emerged millions of years later as carbon dioxide. Therefore, for a short period of time there was a higher ratio of carbon-13 to carbon-12 on Earth, explaining the Lomagundi event. “It’s kind of a big cyclic process,” Eguchi said.

Rajdeep Dasgupta, co-author of the paper, said: “It looks like Earth’s history is calling for tectonics to play a big role in habitability, but that doesn’t necessarily mean that tectonics is absolutely necessary for oxygen build up.”

Dasgupta is the principal investigator for CLEVER Planets, a NASA-led project studying the prospect of life on exoplanets, and believes that there may be other ways besides tectonic activity to kickstart the production of oxygen needed for life. ®

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