London: Ancient microbes may have been producing oxygen through photosynthesis as long as 3.6 billion years ago – a billion years earlier than thought, a study has found.
The findings show that cyanobacteria may not have been the earliest oxygen-producing microbes which means oxygen was available for living organisms very close to the origin of life on earth.
Researchers from Imperial College London (ICL) in the UK studied the molecular machines responsible for photosynthesis and found the process may have evolved as long as 3.6 billion years ago.
The study, published in the journal Heliyon, can help solve the controversy around when organisms started producing oxygen - something that was vital to the evolution of life on earth, said Tanai Cardona, from ICL.
It also suggests that the microorganisms we previously believed to be the first to produce oxygen – cyanobacteria – evolved later, and that simpler bacteria produced oxygen first.
"The process that sustains almost all life on earth today may have been doing so for a lot longer than we think," said Cardona.
"It may have been that the early availability of oxygen was what allowed microbes to diversify and dominate the world for billions of years," he said.
"What allowed microbes to escape the cradle where life arose and conquer every corner of this world, more than 3 billion years ago," he said.
Photosynthesis is the process that sustains complex life on earth - all of the oxygen on our planet comes from photosynthesis. There are two types of photosynthesis: oxygenic and anoxygenic.
Oxygenic photosynthesis uses light energy to split water molecules, releasing oxygen, electrons and protons.
Anoxygenic photosynthesis use compounds like hydrogen sulphide or minerals like iron or arsenic instead of water, and it does not produce oxygen.
Previously, scientists believed that anoxygenic evolved long before oxygenic photosynthesis, and that the earth's atmosphere contained no oxygen until about 2.4 to 3 billion years ago.
Oxygenic and anoxygenic photosynthesis both use an enzyme called Photosystem I.
The core of the enzyme looks different in the two types of photosynthesis, and by studying how long ago the genes evolved to be different, Cardona could work out when oxidative photosynthesis first occurred.
He found that the differences in the genes may have occurred more than 3.4 billion years ago - long before oxygen was thought to have first been produced on earth.
This is also long before cyanobacteria - microbes that were thought to be the first organisms to produce oxygen - existed.
This means there must have been predecessors, such as early bacteria, that have since evolved to carry out anoxygenic photosynthesis instead.
"This is the first time that anyone has tried to time the evolution of the photosystems," said Cardona.
"The result hints towards the possibility that oxygenic photosynthesis, the process that have produced all oxygen on earth, actually started at a very early stage in the evolutionary history of life - it helps solve one of the big controversies in biology today," he said.