For the vast majority of animals on Earth, breathing is synonymous with life. However, during the first 2 billion years of our planet’s existence, oxygen was in a rare state.
This is not to say that Earth had no life all that time, but that life was rare and very different from what we know today.
It was only when more complex bacteria capable of photosynthesis appeared on the scene that everything began to change, unleashing what scientists call the Great Oxidation Event. But when did all this happen? How did all this shake?
A new gene analysis technique has provided clues to a new timeline. It is estimated that it took 400 million years for bacteria to gobble up the sun’s rays and exhale the oxygen before life could actually flourish.
In other words, there may have been organisms on our planet capable of photosynthesis long before the Great Oxidation Event.
“In evolution, things always start small.” explain Geologist Greg Fournier of the Massachusetts Institute of Technology.
“Although there is evidence for early oxygenic photosynthesis, which is the most important and surprising evolutionary innovation on Earth, it took hundreds of millions of years to take off on Earth.”
Currently, there are two competing versions to explain the evolution of photosynthesis in special bacteria known as cyanobacteria. Some believe that the natural process of converting sunlight into energy appeared on the evolutionary scene very early, but it developed “with a slow fuse”. Others believe that photosynthesis evolved later, but it “worked like wildfire.”
Much of the controversy stems from assumptions about the speed with which bacteria evolve and different interpretations of the fossil record.
So Fournier and his colleagues added another form of analysis to the mix. In rare cases, bacteria can sometimes inherit genes not from their parents, but from other, distantly related species. This can happen when another cell “eats” and incorporates other genes into its genome.
Scientists can use this information to find out the relative ages of different bacterial groups; For example, those with stolen genes must have modified them from a species that was present at the same time.
These relationships can be compared to more specific dating attempts, such as molecular clock models, which use the genetic sequences of organisms to trace the history of genetic changes.
To this end, the researchers combed the genomes of thousands of bacterial species, including cyanobacteria. They were looking for cases of horizontal gene transfer.
In total, they identified 34 clear examples. By comparing these examples with six molecular clock models, the authors found that one model in particular was always more appropriate. Choosing this type of mixing, the team made estimates of the life span of the photosynthetic bacteria.
The results indicate that all cyanobacteria living today have a common ancestor that was about 2.9 billion years ago. Meanwhile, grandparents those The ancestors of non-photosynthetic bacteria diverged about 3.4 billion years ago.
Photosynthesis probably evolved somewhere between these two dates.
According to the team’s preferred evolutionary model, cyanobacteria may have made photosynthetically at least 360 million years before geosynchronous orbit. If they are right, this supports the “slow melting” hypothesis.
“This new paper sheds fundamental new light on the history of Earth’s oxygenation by linking the fossil record, in new ways, to genome data, including horizontal gene transfers.” He says Biochemist Timothy Lyons, of the University of California, Riverside.
“The findings speak to the beginnings of biological oxygen production and its ecological importance, in ways that provide vital constraints on early ocean oxygenation patterns and controls and subsequent atmospheric accumulation.”
The authors hope to use similar genetic analysis techniques to analyze organisms other than cyanobacteria in the future.
The study was published in Proceedings of the Royal Society B.
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