Roughly 2.5 billion years ago, Earth experienced the greatest change in its history. Geological records show that molecular oxygen went from being virtually non-existent to skyrocketing and being freely available everywhere.
Evidence of the Great Oxygenation Event (GOE) can be clearly seen in banded iron formations containing oxidized iron. The GOE allowed respirators or oxygen-using organisms to inevitably evolve, including humans.
Understanding the Mysteries of the Great Oxygenation Event
Professor Dan Tawfik from the Weizmann Institute of Sciences explains that dating the Great Oxygenation Event is indisputable with molecular oxygen produced by photosynthetic microorganisms. Chemically, energy taken from light splits water into protons and oxygen. Electrons are then produced in the process where energy-storing compounds like sugars and oxygen become a by-product of their surroundings.
However, the mystery of the Great Oxygenation Event leaves the question of whether oxygen production coincided with the GOE or was living organisms able to access low levels of oxygen before the change.
On the one hand, scientists argue that molecular oxygen wouldn't have been available prior to the GOE as the atmospheric and oceanic chemistry before the event has ensured oxygen release via photosynthesis would immediately react chemically.
Meanwhile, others argue that the oxygen produced by photosynthetic microorganisms may have remained free for non-photosynthetic organisms even before the GOE.
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Studying the GOE
A research student under Tawfik's group, Jagoda Jablonska thought that the focus should be on protein evolution which could finally resolve the issues of the GOE. This process utilizes methods in tracing the evolution of various proteins which would help Tawfik understand when living organisms began to process oxygen.
Phylogenetic trees have been widely used to unravel historical evidence of species and protein families. Jablonska decides to use a similar approach to unravel the mysterious evolution of oxygen-based enzymes during the GOE.
In a study published in the journal Nature Ecology & Evolution entitled, "The evolution of oxygen-utilizing enzymes suggests early biosphere oxygenation," Jablonska detailed evidence unearthed by sampling 130 known families of enzymes that either made or used oxygen in bacteria and archaea that would have been around since the Archean Eon roughly 4 billion years ago.
Findings from Jablonska's research showed a sudden burst of oxygen-based enzyme evolving estimated 3 billion years ago or nearly half a billion years prior to the Great Oxygenation Event.
Further examining the timeline, researchers found that rather than coinciding with the sudden takeover of atmospheric oxygen as others suggested, a burst dated to the time that bacterium left the oceans started colonizing land.
Some oxygen-using enzymes can even be traced back further. If oxygen use coincided with the GOE, the enzymes using oxygen would have evolved much later. Hence, the findings support the theory in which oxygen was already known to some life forms by the time the Great Oxygenation Event took place.
Tawfik explains that the study confirms the earlier hypothesis that oxygen appeared and persisted within the biosphere long before the GOE happened. Although it took time before higher GOE levels were achieved, by then oxygen was widely known and used in the biosphere.
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