New theory: Earth’s longer days triggered oxygen growth

LAKE HURON, Mich. (AP) – Scientists have a new idea of ​​how the Earth got its oxygen: it’s because the planet has slowed down and the days have grown longer.

A study published on Monday proposes and tests the theory that longer, continuous daylight caused strange bacteria to produce a lot of oxygen, making most of life as we know it possible.

They dredged gooey purple bacteria from a deep sinkhole in Lake Huron and tinkered with the amount of light they were getting in lab experiments. The more continuous light the smelly germs received, the more oxygen they produced.

One of the great mysteries of science is how the Earth went from a planet with minimal oxygen to the breathable air we have now. Scientists have long believed that microbes called cyanobacteria were involved, but couldn’t tell what triggered the great oxygenation event.

Researchers in a study published Monday in Nature Geoscience hypothesized that slowing the Earth’s rotation, which has gradually lengthened the days from six hours to the current 24 hours, was essential for cyanobacteria to return the planet more breathable.

Around 2.4 billion years ago, there was so little oxygen in Earth’s atmosphere that it could barely be measured, so that no animal or plant life as we know could live. . Instead, many microbes breathed in carbon dioxide and, in the case of cyanobacteria, produced oxygen in the first form of photosynthesis.

At first it wasn’t much, but in just around 400 million years Earth’s atmosphere has grown to one-tenth the amount of oxygen we have now – a huge leap, the lead author said. of the study, Judith Klatt, biogeochemist at the Max Planck Institute. in Germany. This oxygen explosion allowed plants and animals to evolve, with other plants now joining the oxygen-making party, she said.

But why did the bacteria go on the oxygen-making frenzy? That’s where the University of Michigan oceanographer Brian Arbic comes in. He studies the forces of the tides on Earth and how they slowed the rotation of the Earth. Arbic was listening to a colleague’s talk on cyanobacteria and he noticed that the oxygen event coincided with the lengthening of the days of Earth’s days. The planet’s rotation slows down due to the complicated physics of tidal friction and the interaction with the moon.

Researchers in Michigan and Germany put their theory to the test with bacteria similar to what would have existed around 2.4 billion years ago. They used purple and white mats of cyanobacteria living in a strange world of the nearly 79-foot-deep sinkhole in Lake Huron.

“We actually imagine the world looked a bit like Middle Island sinkhole for most of its history,” Klatt said.

The divers lifted up the gelatinous mats of bacteria, which smelled like rotten eggs. Klatt and his colleagues exposed them to varying amounts of light, for up to 26 hours at a time. They found that more continuous light caused microbes to produce more oxygen.

The study’s authors and outside scientists said this was only a possible but plausible explanation for the increase in oxygen on Earth.

What makes the idea so impressive is that it doesn’t require large biological changes in bacteria or the world’s oceans, said Tim Lyons, professor of biogeochemistry at the University of California, Riverside, who does was not part of the research team.

The Associated Press’s Department of Health and Science receives support from the Howard Hughes Medical Institute’s Department of Science Education. The AP is solely responsible for all content.

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