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Here’s a new twist on how the earth became an oxygen-rich planet: As the rotation of our planet slowed, microbes immersed themselves in longer periods of the sun, which accelerated their release of oxygen into the atmosphere.
Every breath is possible because dense layers of cyanobacteria, the first life on earth, began to produce oxygen billions of years ago as a by-product of photosynthesis. But scientists still weren’t sure what sparked two transformative oxygenation events that transformed Earth from an oxygen-poor planet to an oxygen-rich world where complex organisms could evolve and diversify.
Now researchers have identified an important factor that may have stimulated the release of oxygen by microbes: the slowing of the earth’s rotation, which began about 2.4 billion years ago. The earth spun faster than it was a newborn planet, and completed one rotation in just a few hours. but it gradually slowed down over hundreds of millions of years. Once the length of a day reaches a certain threshold, possibly during those important oxygenation periods, Longer rays of sunshine could have caused more oxygen molecules to hop from areas of high concentration (within the bacterial mats) to areas of lower concentration (the atmosphere), according to a new study.
Scientists recently found evidence in a sinkhole at the bottom of Lake Huron. Bounded by Michigan in the United States and Ontario in Canada, Lake Huron is one of the largest freshwater lakes in the world. The lake’s Middle Island sink-hole measures 91 meters (300 feet) in diameter & lies about 24 m (80 feet) below the surface. There, the sulfur-rich water nourishes colorful microbes that thrive in a low-oxygen environment, just like the earliest forms of bacteria on earth.
Two types of microbes live in the icy depths of the sinkhole: purple cyanobacteria, which seek sunlight, which produce oxygen through photosynthesis, and white bacteria, which consume sulfur and release sulfate instead. The microbes fight for their position all day long, with the sulfur bacteria covering their purple neighbors in the morning and evening hours and blocking access to the sun for the purple microbes. However, when daylight is at its strongest, white microbes avoid the light and migrate deeper. in-to sink-hole, leaving the purple cyanobacteria uncovered and thus able to photosynthesize and release oxygen.
Similar competitions could have occurred billions of years ago between microbial communities, with the exposure to sunlight of the oxygen-producing bacteria being hampered by their microbial neighbors, the researchers write in the study. Then, as the days on Earth got longer, the oxygen producers gained more time in the sunlight. – and more oxygen is released into the atmosphere.
“We recognized that there is a fundamental relationship between the dynamics of light and the release of oxygen, and this relationship is based on the physics of molecular diffusion,” when thermal changes cause molecules to migrate from areas of higher concentration to lower areas. said the lead author of the study. Judith Klatt, scientist at the Max Planck Institute for Marine Microbiology in Bremen.
“A shorter day would allow less oxygen to escape from a mat, even if the same amount of oxygen is being produced per hour,” Klatt told said.
Spin Cycle
Now the earth makes a full rotation on its axis every 24 hours, but more than 4 billion years ago a day lasted only about six hours, the researchers reported. For billions of years, the continual dance of the earth with the moon has slowed the planet’s rotation through a process known as tidal friction. As the earth rotates, the gravitational pull of the moon (and to a lesser extent the sun) attracts the earth’s oceans. This expands the oceans so that they bulge from the center of the earth, siphoning energy from the rotation & slowing it down, said study co-author Brian Arbic. Professor of the Department of Earth and Environmental Sciences, at University of Michigan , Arts and Science.
This slowdown is small, but it added hours of extra daylight over hundreds of millions of years; and the slowdown continues today, Arbic said.
“The tidal friction continues to slow the rate of rotation; the days keep getting longer over geological time,” said Arbic.
Breath Of Fresh Air
The researchers modeled scenarios with different day length and oxygen escape from the microbial mats, and when they compared their models to an analysis of competing microbial mats from the Middle Island sinkhole, they found confirmation of their predictions: photosynthetic bacteria released more oxygen When the days are the longest.
This was not because the microbes were photosynthesizing more; Rather, it is because longer exposure to the sun causes more oxygen to escape from the mats in a single day, says study co-author Arjun Chennu, researcher at the Leibniz Center for Tropical Marine Research in Bremen.
“This subtle decoupling of oxygen release from sunlight is at the heart of the mechanism,” Chennu said in a statement.
The Earth’s atmosphere took shape after the planet formed and cooled about 4.6 billion years ago, and was composed primarily of hydrogen sulfide, methane, and carbon dioxide (CO2), up to 200 times the amount of CO2, as atmosphere is like today, according to the Smithsonian Center for Environmental Research.
All this changed after the Great Oxidation Event (GOE) about 2.4 billion years ago, followed by the Neoproterozoic oxidation event about 2 billion years later, bringing the oxygen content in the atmosphere to about 21% of the current level. These two oxidation events were previously related to the activity of photosynthetic cyanobacteria, and this new evidence suggests that another factor may be a day-time on earth, “A factor that has been largely ignored before”-it becomes long enough to cause more oxygen to be released from the microbial mat, “working in parallel with the other oxygenates suggested previously,” Kratt said.
The findings were published in the journal Nature Geoscience.
