Around 540 million years ago, the strange Ediacaran world was destroyed—dramatically swept aside in the most important moment in the history of evolution when the spectacular supernova of biology, the Cambrian Explosion, was detonated and the world of animal life was born.
“It is remarkable to think that our oldest animal ancestors—and therefore all of us—may owe our existence, in part, to an unusual episode of plate tectonics over half a billion years ago” said Tim Lenton, professor of Climate Change and Earth System Science with the University of Exeter’s Global Systems Institute.
The quest to discover what drove this most important evolutionary events in the history of life on Earth has taken a new, fascinating twist. A team of scientists have given a fresh insight into what may have driven the Cambrian explosion.
While a number of theories have been put forward to explain this landmark period, the most credible is that it was fueled by a significant rise in oxygen levels which allowed a wide variety of animals to thrive.
The new study suggests that such a rise in oxygen levels was the result of extraordinary changes in global plate tectonics. During the formation of the supercontinent ‘Gondwana’, there was a major increase in continental arc volcanism—chains of volcanoes often thousands of miles long formed where continental and oceanic tectonic plates collided. This in turn led to increased ‘degassing’ of CO2 from ancient, subducted sedimentary rocks.
This, the team calculated, led to an increase in atmospheric CO2 and warming of the planet, which in turn amplified the weathering of continental rocks, which supplied the nutrient phosphorus to the ocean to drive photosynthesis and oxygen production.
The study was led by Josh Williams, who began the research as an MSc student at the University of Exeter and is now studying for a Ph.D. at the University of Edinburgh.
During his MSc project he used a sophisticated biogeochemical model to make the first quantification of changes in atmospheric oxygen levels just prior to this explosion of life.
One of the great dilemmas originally recognized by Darwin is why complex life, in the form of fossil animals, appeared so abruptly in what is now known as the Cambrian explosion.”Many studies have suggested this was linked to a rise in oxygen levels—but without a clear cause for such a rise, or any attempt to quantify it,” said Co-author and project supervisor Lenton.
Not only did the model predict a marked rise in oxygen levels due to changes in plate tectonic activity, but that rise in oxygen—to about a quarter of the level in today’s atmosphere—crossed the critical levels estimated to be needed by the animals seen in the Cambrian explosion.
“What is particularly compelling about this research is that not only does the model predict a rise in oxygen to levels estimated to be necessary to support the large, mobile, predatory animal life of the Cambrian, but the model predictions also show strong agreement with existing geochemical evidence,” added Williams.
The image at the top of the page is a simulation of iron-60 atoms dispersed by multiple supernovae close to the solar system 2.2 million years ago. Some of that iron still lies at the bottom of the oceans and on the moon. With thanks to Science and Michael Schulreich