If time travelers could travel back to the early Earth, say three billion years before the present, they should bring life support with them.
They’d swiftly suffocate because there was so little oxygen on the globe at the time.
Without breathing oxygen, the time explorers would perish before witnessing another feature of early Earth: the sun rising every 16 to 17 hours or so.
According to a new theory, the connection between short days and low oxygen levels could be more than a coincidence.
Researchers have long been perplexed by how Earth’s oxygen levels appear to have climbed inexorably over time.
Around two billion years ago, the earth had essentially no oxygen and then quickly increased to roughly a few percent of its current abundance—an event known as the Great Oxidation Event.
After that, oxygen levels leveled out for a boring billion years before increasing dramatically again.
Who do we owe all of this breathable oxygen to? Photosynthesizing bacteria, which release oxygen while producing energy from sunlight, are credited by biologists.
Except the timing is all off. Such microorganisms are thought to have formed long before the initial oxygen jump, and it’s unclear what slowed them down during the dull billion.
“How come, if oxygenic photosynthesis is driving the growth of oxygen, it stopped for such a long time and then restarted?” Arjun Chennu, a data scientist and biologist at Germany’s Leibniz Center for Tropical Marine Research, agrees.
HOW WAS THE EARTH OXYGENATED BY THE MOON?
Many theories have emerged over time to explain the oxygen jumps. Volcanic gas, which absorbs oxygen, may have decreased.
Maybe the early environment lacked the resources that cyanobacteria (those oxygen-producing germs) needed to survive.
However, Judith Klatt, a microbiologist at the Max Planck Institute for Marine Microbiology, was intrigued by a curious coincidence: when oxygen levels climbed, the days grew longer.
Once every six hours or so, the Earth completed a full rotation near the beginning of its existence.
However, as oceans formed and the moon’s gravitational pull sloshed those waters back and forth across the crust, friction extended the planet’s rotation to the current 24 hours (and the days continue to lengthen, growing by one one-hundred-thousandth of a second each year).
However, that steady decline hasn’t been consistent. According to one popular belief, there are two sorts of tides:
For possibly a billion years, some in the ocean and others in the atmosphere may have resisted and neutralized each other, keeping the day at 21 hours long.
a cease-fire that happens to fall on the dull billion, as well as the oxygen, rises that bookend it
Klatt sought Chennu to figure out the specifics of how the era’s microorganisms might have reacted to longer days.
She was familiar with microbial mats, millimeter-thin layers of cyanobacteria, and a variety of other species that clung to coastal rocks and sediments for much of Earth’s history thanks to her postdoctoral studies at the University of Michigan.
She assumed that their oxygen production was affected by the duration of the day.
Chennu’s model suggested that this was the case. The creation of oxygen was crucially dependent on how quickly the sunshine shifted.
The cyanobacteria couldn’t ramp up to their maximal oxygen output before dusk because the Earth spun too swiftly.
They were able to reach their full oxygen-producing capacity as the Earth’s daily rotation slowed.
“It’s a little influence, but it can generate changes that we believe are insignificant on every light day for millions of years,” Chennu says.
The team’s findings were published in Nature Geoscience on Monday.
Divers obtained sample microbial mats from Lake Huron to test their simple model against the complexities of reality.
These were multi-microbe colonies, including those that competed with the cyanobacteria for the best sun-absorbing location at the top of the mat.
When the researchers used artificial light to replicate day lengths of 12, 16, 21, and 24 hours, the mats released the most oxygen on the longest days—much more than the first model predicted.
IN SEARCH OF MORE PAST CLUES IN THE FUTURE
The researchers state that their findings are based on several assumptions.
Microbial mats, for example, must have been numerous, according to the fossil record.
However, researchers’ knowledge of the Earth’s rotation rate and oxygen abundances so far back in time is likewise hazy and speculative.
Klatt says, “It was a long time ago.” “The oldest rocks date back 3.8 billion years and are extremely unusual.
However, if the Earth’s spin-down standstill coincides with the bored billion, their hypothesis takes care of the rest.
Longer days resulted in more oxygen until cyanobacteria overcame Earth’s natural ability to absorb oxygen, resulting in the Great Oxidation Event.
The spin-stabilized was then used for the boring billion. Finally, the days began to lengthen again, and oxygen levels began to rise once more.
Many years later, budding trees took over and increased oxygen levels to current levels.
Klatt believes that previous theories describing the Great Oxidation Event may have also played a role.
Rather than competing with them, the new day length concept enhances them. According to Klatt, “there are probably a million more systems running at the same time.”
Following that, the team expects that other researchers will improve on their simple estimate of how everyday oxygen production might lead to long-term changes in the atmosphere.
They also anticipate the discovery of yet-to-be-discovered caches of ancient rocks that could provide more detailed images of the early Earth.
Future missions may be able to gather lunar rocks that include a more detailed record of how the moon has slowed the Earth through tides over time.
Any one of these lines of evidence could shed light on the link between the planet’s rotation and the air we breathe.
Chennu says, “We’re hopeful that this technique will serve as a linchpin for thinking about this boring billion-year problem.”