Breath is synonymous with life for the majority of animals on Earth. However, oxygen was scarce for 2 billion years of the planet's existence.
This doesn't necessarily mean Earth died, but it does indicate that Earth lived for a very short time.
Only when more sophisticated bacteria could photosynthesize appeared on the scene, did everything begin to change. This is what scientists call a Great Oxidation Event. How did this all happen? How did it all happen?
New gene-analyzing techniques have provided clues to a new timeline. It took bacteria 400 million years to absorb sunlight and exhale oxygen in order for life to thrive.
This means that there was a possibility of organisms living on the planet that could photosynthesize long before the Great Oxidation Event.
Greg Fournier, a geobiologist at the Massachusetts Institute of Technology, says that "in evolution things always start small."
"Even though evidence exists for early oxygenic photosynthesis, which is the single most important evolutionary innovation on Earth, it took hundreds of millions to get it off the ground."
There are currently two narratives that explain how photosynthesis evolved in special bacteria called cyanobacteria. While some believe that the natural process of converting sunlight into energy was discovered early in evolution, others think it took longer to develop. Others believe photosynthesis evolved later, but it "took off like wildfire".
Many of the differences are due to assumptions about how fast bacteria evolves and differing interpretations of fossil records.
Fournier and his coworkers have added an additional form of analysis to their arsenal. Rarely, genes can be inherited from distantly related species, rather than from their parents. This happens when one cell "eats" another and incorporates its genes into its own genome.
This information can be used by scientists to determine the relative ages between different bacterial groups. For example, researchers can use it to determine if a species which existed at the same moment as them has stolen their genes.
These relationships can be compared with more specific dating efforts, such as molecular clock models that use the genetic sequences and organisms to trace a history in genetic changes.
Researchers searched through thousands of bacteria species' genomes, including cyanobacteria, to find these cases. They were searching for horizontal gene transfer cases.
They identified 34 examples. The authors found that one of these examples was the most consistent when compared to six molecular-clock models. The team selected this model from the mix and ran estimates to determine how old the photosynthesizing bacteria are.
These findings indicate that all cyanobacteria species today share a common ancestor, which was around 2.9 billion years old. The ancestors of these ancestors split off from non-photosynthetic bacteria around 3.4 billion years back.
Most likely, photosynthesis evolved sometime between these two dates.
According to the preferred evolutionary model of the team, cyanobacteria probably photosynthesized at least 360 million year before the GEO. This supports their "slow fuse” hypothesis if they are correct.
Timothy Lyons, a biogeochemist at the University of California at Riverside, says that "this new paper sheds essential light on Earth’s oxygenation history through bridging, with novel ways, fossil records with genomic data including horizontal gene transfer,"
"The results show that the beginnings of biological oxygen production are evident, as well as its ecological significance. They also provide important constraints and controls on the patterns and controls for the early oxygenation of the oceans, and the later accumulations in atmosphere.
They hope to be able to use the same gene analysis techniques for organisms other than cyanobacteria.
Proceedings of the Royal Society B published the study.
