When Earth’s 6-Hour Days Grew, So Did Our Oxygen



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Scientists have a new idea for how Earth got its oxygen: It’s because the planet slowed down and days got longer. A study published Monday proposes and puts to the test the theory that longer, continuous daylight kick-started weird bacteria into producing lots of oxygen, making most of life as we know it possible, per the AP. They dredged up gooey purple bacteria from a deep sinkhole in Lake Huron and tinkered with how much light it got in lab experiments. The more continuous light the smelly microbes got, the more oxygen they produced. One of the great mysteries in science is just how Earth went from a planet with minimal oxygen to the breathable air we have now. Scientists long figured microbes called cyanobacteria were involved, but couldn’t tell what started the great oxygenation event.

Researchers in a study in Nature Geoscience theorize that Earth’s slowing rotation, which gradually lengthened days from six hours to the current 24 hours, was key for the cyanobacteria in making the planet more breathable. About 2.4 billion years ago there was so little oxygen in Earth’s atmosphere that it could barely be measured, so no animal or plant life like we know could live. Instead, lots of microbes breathed in carbon dioxide, and in the case of cyanobacteria, produced oxygen in the earliest form of photosynthesis. At first it wasn’t much, but in only about 400 million years Earth’s atmosphere went to one-tenth the amount of oxygen we have now—a huge jump, said the study’s lead author, Judith Klatt of the Max Planck Institute in Germany. That oxygen burst allowed plants and animals to evolve, with other plants now joining in the oxygen-making party, she said.

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