Microbes have been able to oxygenate photosynthesis at least a billion years earlier in Earth’s history than previously thought.
This hypothesis put forward by British biologists at Imperial College London has upset the widely accepted theory of the moment of the appearance of complex life on Earth and its evolution.
It also allows to consider otherwise its probable evolution on other planets.
The oxygen present in the earth’s atmosphere is necessary for complex life forms that use it during aerobic respiration to produce energy.
Oxygen levels have increased dramatically in the atmosphere about 2.4 billion years ago, but the reasons for this increase are debated.
Some scientists believe that 2.4 billion years ago, cyanobacteria developed for the first time. Cyanobacteria are organisms whose photosynthesis was oxygenated.
Other scientists claim that cyanobacteria have evolved well before 2.4 billion years ago, but that something has prevented the accumulation of oxygen in the air.
It should be noted that cyanobacteria perform a relatively sophisticated form of oxygenated photosynthesis, a type similar to current plants.
It has therefore been suggested that simpler forms of oxygenated photosynthesis could have existed earlier, even before the appearance of cyanobacteria, a reality that would have led to low levels of oxygen available for life.
The present work has established that oxygenated photosynthesis occurred at least one billion years before the appearance of cyanobacteria, and that it could have appeared very early in the 4.5 billion years of the history of the Earth.
We know that cyanobacteria are very old, but we do not know exactly when they appeared. For example, if cyanobacteria are 2.5 billion years old, it means that oxygenated photosynthesis may have started 3.5 billion years ago.
“This suggests that it would not take billions of years for a process like oxygenated photosynthesis to begin after the origin of life,” adds Dr. Cardona.
Thus, if oxygenated photosynthesis has evolved early, this could mean that it is a relatively simple evolutionary process of evolution. The probability that a complex life emerges on a distant exoplanet would therefore be higher than previously thought.
The details of this work are published in the journal Geobiology.