It took 100 million years for oxygen levels in the oceans and atmosphere to increase to the level that allowed the explosion of animal life on Earth about 600 million years ago, according to study funded by the Natural Environment Research Council. Before now it was not known how quickly Earth’s oceans and atmosphere became oxygenated and if animal life expanded before or after oxygen levels rose.
The new study, published today in Nature Communications, shows the increase began significantly earlier than previously thought and occurred in fits and starts spread over a vast period. It is therefore likely that early animal evolution was kick-started by increased amounts of oxygen, rather than a change in animal behaviour leading to oxygenation.
Lead researcher, Dr Philip Pogge von Strandmann (UCL Earth Sciences), said: “We want to find out how the evolution of life links to the evolution of our climate. The question on how strongly life has actively modified Earth’s climate, and why the Earth has been habitable for so long is extremely important for understanding both the climate system, and why life is on Earth in the first place.”
Researchers tracked what was happening with oxygen levels globally 770 – 520 million years ago (Ma) using new tracers in rocks across the US, Canada and China. Samples of rocks that were laid down under the sea at different times were taken from different locations to piece together the global picture of the oxygen levels of Earth’s oceans and atmosphere. By measuring selenium isotopes in the rocks, the team revealed that it took 100 million years for the amount of oxygen in the atmosphere to climb from less than 1% to over 10% of today’s current level. This was arguably the most significant oxygenation event in Earth history because it ushered in an age of animal life that continues to this day.