Evolution on earth was delayed by two billion years because of low level atmospheric oxygen, according to researchers from the University of Exeter.

The scientists discovered that until there was a large rise in the number of land plants and photosynthesis increased, oxygen consumption and production remained in equilibrium. This balance ensured oxygen levels remained low.

Professor Lenton, from the University of Exeter and study co-author, said: This time in Earths history was a bit of a catch-22 situation. It wasnt possible to evolve complex life forms because there was not enough oxygen in the atmosphere, and there wasnt enough oxygen because complex plants hadnt evolved It was only when land plants came about did we see a more significant rise in atmospheric oxygen.

Using a bespoke computer model, the research attempted to understand why the great oxidation event 2.4bn years ago did not generate modern levels of oxygen. In their paper in Nature Communications, they explain how organic material accumulated in the Earths sedimentary rock. After exposure to the atmosphere, this material reacted with oxygen for the first time, creating a feedback loop of oxygen exposure and consumption.

After the increase in land plants and a doubling of photosynthesis increasing levels of oxygen disturbed the equilibrium. The scientists model suggests even though oxygen levels at the time were only between 1 and 10% of present day levels, this was high enough to help complex life to evolve on land.

Professor Lenton said: The history of life on Earth is closely intertwined with the physical and chemical mechanisms of our planet. It is clear that life has had a profound role in creating the world we are used to, and the planet has similarly affected the trajectory of life. I think its important people acknowledge the miracle of their own existence and recognise what an amazing planet this is.

The first life on Earth is believed to have begun with bacterial evolution almost four billion years ago. It was not until 600 million years ago that the first multi-cellular animals such as jellyfish and sponges were found in the ocean. Humans did not appear on Earth until 200,000 years ago.

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Evolution held back by lack of oxygen - Lab News