How was the Earth oxygenated?
The emergence of an oxygenated atmosphere was not a one time advance but likely happened after a series of smaller fluctuations.
That’s one of the findings from a new study called “Transient episodes of mild environmental oxygenation and oxidative continental weathering during the late Archean” that was published recently in the journal Science Advances.
Researchers from the University of Alberta, University of Waterloo, Arizona State University, University of California Riverside, and Georgia Institute of Technology, collaborated to examine sedimentary rocks in Western Australia and found that before the “Great Oxidation Event” about 2.4-billion year ago, levels of oxygen fluctuated until oxygenation became a permanent condition of the Earth.
“The onset of Earth’s surface oxygenation may have been a complex process characterized by multiple ‘whiffs’ of O2 until a tipping point was crossed,” says Brian Kendall, a professor of Earth and Environmental Sciences at the University of Waterloo and the paper’s lead author.
A widely accepted theory of The Great Oxygenation Event points to prokaryotic and then later eukaryotic organisms who lived 3500-million years ago. These organisms, says the theory, carried out oxygenic photosynthesis and produced oxygen as a waste product.
The findings from the recent Canadian-led study back up those of another from the University of California, Riverside that was published last year in Nature. The lead author of that study, Professor Timothy Lyons, says the “Great Oxidation Event” is actually a misnomer because the process was so gradual.
“A big message of this paper is that the Great Oxidation Event is really a very protracted and dynamic transition rather than a single step,” says Lyon. “We suggest it shouldn’t be called an event at all.”
The rise of oxygen levels on earth gave rise to the development of more complex organisms, but was stalled for a long time after the “Great Oxidation Event” a time many scientists refer to as “the boring billion”. Lyons believes a second oxygenation event that happened 800-million years ago was the actual catalyst. Another scientist believes that multiple conditions, not just oxygen levels had to be present to produce complex life.
Malcolm Walter, a geobiologist at the University of New South Wales in Sydney, Australia, says genetic innovations were also part of what brought on the Cambrian Explosion, a relatively short period of time when most major animal phyla appeared.
“Until the environment was right, and until genetics tools were there, [the evolution of complex life] couldn’t have happened,” says Walter.
Back in Canada, Rob Creaser, professor of earth and atmospheric sciences at the University of Alberta, says the data for the Canadian-led study was only available because the facilities in Alberta are world-class.
“We are tracking atmospheric changes through time to understand how oxygen increased to the level needed to support complex life,” says Creaser. “When the Earth first formed, there was no oxygen in the atmosphere. Our analytical facilities here at the U of A allowed us to conduct precise analyses of this rock sample to understand the tempo at which that oxygen built up through photosynthesis.”