The Great Oxidation Event occurred as a result of cyanobacteria, pumping out unwanted oxygen, which in turn, transformed Earth's atmosphere. But while this explains how it the GOE happened, it doesn't explain why, and it doesn't really explain when it happened. The issue is that cyanobacteria seem to have been around long before the GOE.
"They're probably among the first organisms we have on this planet," says Bettina Schirrmeister of the University of Bristol in the UK. We can be confident that there were cyanobacteria by 2.9 billion years ago, because there is evidence of isolated "oxygen oases" at that time. They might date as far back as 3.5 billion years, but it's hard to tell because the fossil record is so patchy. That means the cyanobacteria were busy pumping out oxygen for at least half a billion years before oxygen started appearing in the air. That doesn't make a lot of sense. One explanation is that there were a lot of chemicals around – perhaps volcanic gases – that reacted with the oxygen, effectively "mopping it up".
Some modern cyanobacteria have done something that, by bacterial standards, is remarkable. While the vast majority of bacteria are single cells, they are multicellular. Multicellularity could have been a game-changer for Earth's early cyanobacteria.The individual cyanobacterial cells have joined up into stringy filaments, like the carriages of a train. That in itself is unusual for bacteria, but some have gone further.
Bettina E Schirrmeister research states that: “We conducted and compared phylogenetic analyses of 16S rDNA sequences from a large sample of taxa representing the morphological and genetic diversity of cyanobacteria. We reconstructed ancestral character states on 10,000 phylogenetic trees. The results suggest that the majority of extant cyanobacteria descend from multicellular ancestors. Reversals to unicellularity occurred at least 5 times. Multicellularity was established again at least once within a single-celled clade. Comparison to the fossil record supports an early origin of multicellularity, possibly as early as the "Great Oxygenation Event" that occurred 2.45 - 2.22 billion years ago.”
"They're probably among the first organisms we have on this planet," says Bettina Schirrmeister of the University of Bristol in the UK. We can be confident that there were cyanobacteria by 2.9 billion years ago, because there is evidence of isolated "oxygen oases" at that time. They might date as far back as 3.5 billion years, but it's hard to tell because the fossil record is so patchy. That means the cyanobacteria were busy pumping out oxygen for at least half a billion years before oxygen started appearing in the air. That doesn't make a lot of sense. One explanation is that there were a lot of chemicals around – perhaps volcanic gases – that reacted with the oxygen, effectively "mopping it up".
Some modern cyanobacteria have done something that, by bacterial standards, is remarkable. While the vast majority of bacteria are single cells, they are multicellular. Multicellularity could have been a game-changer for Earth's early cyanobacteria.The individual cyanobacterial cells have joined up into stringy filaments, like the carriages of a train. That in itself is unusual for bacteria, but some have gone further.
Bettina E Schirrmeister research states that: “We conducted and compared phylogenetic analyses of 16S rDNA sequences from a large sample of taxa representing the morphological and genetic diversity of cyanobacteria. We reconstructed ancestral character states on 10,000 phylogenetic trees. The results suggest that the majority of extant cyanobacteria descend from multicellular ancestors. Reversals to unicellularity occurred at least 5 times. Multicellularity was established again at least once within a single-celled clade. Comparison to the fossil record supports an early origin of multicellularity, possibly as early as the "Great Oxygenation Event" that occurred 2.45 - 2.22 billion years ago.”
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