According to a recent study, ancient microbes have been able to produce photosynthetic oxygen a billion years earlier than we thought, 3.6 billion years ago.
Photosynthesis is the process that supports complex life on Earth: all the oxygen in our planet comes from photosynthesis. There are two types of photosynthesis: oxygenic and anoxygenic. Oxygenic photosynthesis uses light energy to divide water molecules, releasing oxygen, electrons and protons. Anoxygenic photosynthesis uses compounds such as hydrogen sulphide or minerals such as iron or arsenic instead of water, and does not produce oxygen.
Previously, scientists thought that oxygen had evolved well before oxygenic photosynthesis, and that the Earth’s atmosphere did not contain oxygen until about 2.4 to 3 billion years ago. However, this new study published in the journal Heliyon suggests that the process of oxygenic photosynthesis may have evolved a billion years ago. This would mean that complex life could have evolved earlier also, and also suggests that it is not the cyanobacteria that evolved later that started producing oxygen but much simpler bacteria.
Instead of trying to detect oxygen in ancient rocks, which had been done previously, Dr. Tanai Cardona of Imperial College London and lead author of this study, looked deep into these molecular machines that perform photosynthesis. Oxygenic and anoxygenic photosynthesis uses an enzyme called photosystem I. The core of the enzyme is different depending on the type of photosynthesis. By studying how long the genes have evolved to be different, the researcher was able to determine that these differences occurred more than 3.4 billion years ago – about 1 billion years earlier than expected . It was also well before the advent of cyanobacteria – the microbes that were thought to be the first organisms to produce oxygen.
“This is the first time anyone has tried to time the evolution of photosystems,” says Dr. Cardona. “The result suggests that oxygenic photosynthesis, the process that produced all the oxygen on Earth, actually began at a very early stage in the evolutionary history of life.”