[ad_1]
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 scarce.
This is not to say that the Earth was lifeless all this time, but that life was scarce and very different from what we know today.
It wasn’t until more complex bacteria capable of photosynthesis appeared that everything started to change, leading to what scientists are calling the great oxidation event. But when did all this happen? How did it all happen?
A new technique of genetic analysis has provided clues to the new timeline. It is estimated that it took 400 million years for bacteria to absorb sunlight and remove oxygen before life really flourished.
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,” says geologist Greg Fournier of the Massachusetts Institute of Technology.
“While there is evidence of early oxygenated photosynthesis – the most amazing evolutionary innovation on Earth – it still takes hundreds of millions of years to take off.”
Currently, there are two competing accounts to explain the evolution of photosynthesis in special bacteria called cyanobacteria. Some believe that the natural process of converting sunlight into energy happened quite early in the evolutionary scene, but progressed with a “slow fuse.” Others believe that photosynthesis evolved later, but that it “happened like wildfire.”
Much of the controversy stems from assumptions about how quickly bacteria evolved and the different interpretations of the fossil record.
Fournier and his colleagues therefore added another form of analysis to the mix. In rare cases, bacteria can sometimes inherit genes not from their parents, but from another distant species. This can happen when another cell “eats” and incorporates other genes into its genome.
Scientists can use this information to determine the relative age of different groups of bacteria; For example, those who stole the genes must have modified them from the species that existed at the same time.
These relationships can then 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, researchers combed through 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 notably found the one that works best. In choosing this mixing model, the team made estimates to determine the actual age of photosynthetic bacteria.
The results indicate that all cyanobacteria living today have a common ancestor around 2.9 billion years ago. Meanwhile, the ancestors 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 likely photosynthesized at least 360 million years before geosynchronous orbit. If they are right, it reinforces the “slow fusion” hypothesis.
“This new article sheds fundamental new light on the history of Earth’s oxygenation by linking the fossil record to genetic data, including horizontal gene transfers, in an unprecedented way,” said biogeochemist Timothy Lyons from the University of California at Riverside.
“The results speak to the beginnings of biological oxygen production and its ecological importance, in a way that provides vital constraints to models and controls on the first oxygenation of the oceans and subsequent accumulation in the atmosphere.”
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.
Source link
