Palaeontologists and evolutionary biologists have earlier identified the "Great Oxidation Event" as the turning point in the history of evolution of life on Earth. The event not only triggered the accumulation of oxygen in the atmospher but also helped in the genesis of new life forms. However, recent study results indicate that the previously held theory of evolution of man and other multicellular life forms may not be entirely correct.

A recent computer-simulated study done by Professor Tim Lenton and Dr. Stuart Daines from the Geography department of the University of Exeter revealed that although oxygen was evolved in the "Great Oxidation Event," it failed to achieve and maintain the atmospheric levels that is necessary for the evolution of multicellular organisms, such as plants and animals, Heritage Daily reported.

The study results published in Nature Communications indicated that the atmospheric oxygen during the low Proterozoic were used up for the oxidative weathering of sedimentary rocks. The carbon-based organic material from buried dead bodies of simple life forms got accumulated in the sedimentary rocks.

It is proposed that tectonic movements must have pushed these organic sediments to the surface of ancient Earth, which facilitated its reaction with atmospheric oxygen. This formed a feedback loop where the oxygen evolved was invested in chemical reactions, thereby causing considerable decrease in the atmospheric oxygen levels, UPI reported.

"This time in Earth's history was a bit of a catch-22 situation. It wasn't possible to evolve complex life forms because there was not enough oxygen in the atmosphere, and there wasn't enough oxygen because complex plants hadn't evolved. It was only when land plants came about did we see a more significant rise in atmospheric oxygen," Professor Tim Lenton said.

The photosynthesizing plants produced oxygen, which oxygenated the atmosphere to concentrations comparable to the present levels. This helped in the evolution of man and other animals.

Another study by the researchers at the University of Washington, which was recently published in the Proceedings of the National Academy of Sciences, indicated a similar pattern. These studies are an indication that presently accepted notions of evolution of man are likely to be changed in the future.