By Nicole Loranger
New research from the University of Exeter’s Geography Department has provided an explanation for the low levels of oxygen in Earth’s atmosphere during the time of the “great oxidation event” about 2.4 billion years ago. As the name suggests, this moment in Earth’s history was the introduction of oxygen- but instead of oxygen existing at present-day levels, it remained at about 10% of that level for reasons that had scientists puzzled. That is, until Professor Tim Lenton and Dr. Stuart Daines of the University of Exeter produced a computer model to demonstrate the factors behind these limited oxygen levels. Due to tectonic plate movement, organic layers of sediment rose to Earth’s surface and reacted with the oxygen in the atmosphere. More oxygen resulted in faster reactions with organic material, maintaining an equilibrium between oxygen production and consumption and preventing oxygen from building up to the levels of today. As Professor Lenton describes, these low-levels of oxygen kept evolution at a stand still. “It wasn't possible to evolve complex life forms because there was not enough oxygen in the atmosphere,” he explains, “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.” With the introduction of land plants, global oxygen levels doubled, disrupting the stability of the cycle and eventually paving the way for the evolution of land animals about 40 million years later. The rest, as they say, is history- and thanks to Lenton and Daines, this particular section of history has become that much clearer, further demonstrating the connection between earth’s chemical composition and the life it has sustained.
University of Exeter. "Low level of oxygen in Earth's middle ages delayed evolution for two billion years: A low level of atmospheric oxygen in Earth's middle ages held back evolution for 2 billion years, raising fresh questions about the origins of life on this planet." ScienceDaily. ScienceDaily, 2 February 2017. <www.sciencedaily.com/releases/2017/02/170202090810.htm>.