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Oxygen in the Earth's atmosphere is fundamental to complex life types, which use it under a vigorous breath to ensure vitality.
Oxygen levels increased dramatically in the climate about 2.4 billion years ago, but it was discussed why this happened. Some researchers estimate that 2.4 billion years ago, creatures called cyanobacteria evolved, which could allow photosynthesis (oxygen).
Other scientists believe that cyanobacteria have evolved well before 2.4 billion years ago, but that something has prevented oxygen from accumulating in the air.
In a new study from Imperial College London, oxygen photosynthesis appeared at least a billion years before cyanobacteria developed. Their results show that oxygenic photosynthesis could have evolved very early in the 4.5 billion Earth's history.
According to the scientists, the discovery could change the ideas on how and when the complex life evolved on Earth, and on the probability that it evolves on other planets.
Dr. Tanai Cardona, lead author of the Imperial Department of Life Sciences, said, "We know that cyanobacteria are very old, but we do not know exactly how old they are. For example, if cyanobacteria are 2.5 billion years old, it means that photosynthesis by oxygen could have started as early as 3.5 billion years ago. This suggests that it would not take billions of years for a process such as oxygenic photosynthesis to start after the origin of life. "
During the study, scientists studied the evolution of two of the major proteins involved in oxygen photosynthesis.
In the first stage of photosynthesis, cyanobacteria use light energy to split water into protons, electrons and oxygen using a protein complex called Photosystem II.
Photosystem II is composed of two proteins called D1 and D2. Initially, the two proteins were the equivalent, but despite having basically the same structure as their structures, their basic genetic sequences are now different.
This demonstrates that D1 and D2 have progressed independently – in cyanobacteria and plants, they offer only 30% of their genetic sequence. Indeed, even in their original form, D1 and D2 would have possessed the ability to perform oxygenic photosynthesis, thus realizing how indiscernible they were before they could discover when this ability would develop in the beginning.
To determine the time difference between J1 and J2 is 100% identical and they represent only 30% of cyanobacteria and plants, the team determined the rate at which proteins evolved – their rate of evolution. Using powerful statistical methods and known events in the evolution of photosynthesis, they determined that Photosystem II's D1 and D2 proteins evolved extremely slowly – even more slowly than some of the proteins the oldest in biology that we believe to be found in the oldest forms of life. .
From there, they calculated that the time between identical D1 and D2 proteins and similar versions at 30% of cyanobacteria and plants is at least a billion years old and could be longer.
Dr. Cardona said: "Usually, the appearance of oxygen photosynthesis and cyanobacteria is considered the same thing. So, to know when oxygen was first produced, researchers tried to find out when the cyanobacterium had evolved for the first time. "
"Our study shows rather that oxygenic photosynthesis probably began well before the ancestor of the most recent ancestor of cyanobacteria. This is consistent with current geological data that suggest that oxygen flushes or localized accumulations of oxygen were possible before three billion years ago. "
Scientists are now trying to recreate the appearance of the photosystem before D1 and D2 have evolved. Using the known variation of the genetic codes of the photosystem in all living species today, they are trying to reconstruct the genetic code of the ancestral photosystem.
They published their story in the journal Geobiology.
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