A new study suggests Earth’s supply of oxygen developed thanks to the planet’s gradually slowing rotation creating longer days that allowed a certain form of algae to admit more oxygen as a byproduct of its metabolic process.
The study, published Monday in the scientific journal Nature Geoscience, suggests that about 2.4 billion years ago there was so little oxygen in Earth's atmosphere, it could barely be measured, so no animal or plant life as we know it could exist.
Much of the life on Earth consisted of tiny microbes, among them, a blue-green form of algae called cyanobacteria, which breathed in carbon dioxide and exhaled oxygen in the earliest form of photosynthesis.
The researchers say about 400 million years ago, the Earth took a relatively enormous leap in the amount of oxygen in its atmosphere, growing from nearly imperceptible levels to one-tenth the amount of oxygen it has now.
The researchers suggest the Earth's rotation, which has been gradually slowing over time, lengthened days from about six hours to about the current 24 hours. The longer days provided more sunlight for the cyanobacteria to produce enough oxygen to give the planet breathable air.
The scientists reached their conclusion by studying microbes found growing in a sinkhole under 80 feet of water in Lake Huron, off the coast of the U.S. state of Michigan. The bacteria exist in an oxygen-poor environment similar to the single-celled cyanobacteria that formed matlike colonies billions of years ago, which carpeted both land and seafloor surfaces.
The researchers dredged up the bacteria from the sinkhole and tinkered with how much light it got in lab experiments. The more continuous light the microbes got, the more oxygen they produced.
That finding, in turn, points to a previously unconsidered link between Earth's oxygenation history and its rotation rate.
The scientists say their models show that this proposed mechanism might help explain the pattern of Earth's oxygenation, as well as the persistence of low-oxygen periods through most of the planet's history.
Some information in this report came from the Associated Press.