Earth’s Longer Days May Have Produced More Oxygen

A group of scientists have come up with a new theory on how the Earth’s atmosphere got its oxygen: the planet has slowed down and the days have grown longer.

A recent study suggests that the longer and more continuous daylight caused bacteria to produce a lot of oxygen. This oxygen has made possible most of life as we know it.

Scientists unearthed colorful, smelly bacteria from a depth abyss in Lake Huron, which is one of the Great Lakes in the northern United States. In laboratory experiments, researchers gave bacteria different amounts of light. They found that bacteria produce oxygen at a higher rate the more continuous light they receive.

One of the great mysteries of science is how the Earth went from a planet with little oxygen to the breathable air we have now. Scientists have long believed that microorganisms called cyanobacteria were involved. But they don’t know what triggered the great oxygenation event.

The researchers published their study in the publication Geosciences of nature this month. This suggests that the Earth is slowing down rotation enabled cyanobacteria to make the atmosphere capable of supporting life. Over a long period of time, the Earth has gone from a six-hour rotation to its current 24-hour rotation.

Scientists say that 2.4 billion years ago there was almost no oxygen in the Earth’s atmosphere. No animal or plant to our knowledge could live in such conditions. Instead, many bacteria breathed in carbon dioxide. In the case of cyanobacteria, they produced oxygen in the oldest form of photosynthesis.

At first, it wasn’t much. But after about 400 million years, Earth’s atmosphere has reached a tenth of the amount of oxygen we have today. It’s a huge leap forward, said study senior editor Judith Klatt. She is an expert at the Max Planck Institute in Germany. The increased oxygen allowed plants and animals to develop over time. And plants have started to join in the oxygen-making party, she said.

But why did the bacteria start to produce more oxygen? Brian Arbic is an ocean expert at the University of Michigan. He studies tide forces on Earth and how they slowed the rotation of the Earth. Arbic says the planet’s rotation has slowed down due to the tide friction and the relationship of the Earth to the Moon.

Researchers at the University of Michigan and Germany tested their ideas with bacteria similar to those that would have existed 2.4 billion years ago. They used white and purple carpet of cyanobacteria living 24 meters underwater in the Lake Huron sinkhole.

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

The divers lifted up the mats of bacteria, which smell like very old eggs. Klatt and others exposed them to varying amounts of light, for up to 26 hours at a time. They found that more continuous light causes bacteria to produce more oxygen.

The study’s authors and outside scientists said this was just one possible reason for the increased oxygen on Earth. What makes the idea interesting is that it doesn’t require big biological changes in bacteria or the world’s oceans, said Tim Lyons. He is a professor at the University of California at Riverside and was not part of the research team.

I am Alice Bryant.

The Associated Press reported this story. Alice Bryant adapted it for Learn English. Mario Ritter, Jr. was the editor.

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Words in this story

abyss -not. a low area in the ground or underwater that is formed by the flow of water removing the soil and underlying rocks

rotation -not. one full turn around a central point; a complete tour of the Earth

photosynthesis -not. the process by which a green plant turns water and carbon dioxide into food and releases oxygen

tide –Adj. related to tides; the push and pull caused by gravity from the sun and moon affecting the world’s oceans

friction -not. the force that makes moving objects slow

carpet -not. a thick mass of something that is stuck together