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Plate tectonics may have triggered Cambrian explosion

By
Brooks Hays
During the formation of the supercontinent Gondwana, a massive chain of volcanoes formed. The subduction of ancient sedimentary rocks freed up trapped CO2, setting off a chain reaction of climate and geologic processes that led to a rise of oxygen levels at the outset of the Cambrian period. Photo by G.E. Ulrich/USGS
During the formation of the supercontinent Gondwana, a massive chain of volcanoes formed. The subduction of ancient sedimentary rocks freed up trapped CO2, setting off a chain reaction of climate and geologic processes that led to a rise of oxygen levels at the outset of the Cambrian period. Photo by G.E. Ulrich/USGS

June 19 (UPI) -- New research suggests the dramatic increase in biodiversity known as the Cambrian explosion was triggered by a massive shift in global plate tectonics.

The Cambrian explosion began 500 million years ago and lasted just 13 million years. During the period, almost all major animal phyla emerged. For decades, scientists have been working to unravel the mysteries of this extraordinary evolutionary outburst.

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Most scientists agree that a sudden rise in oxygen levels on Earth inspired the diversification of animal life. Now, research suggests a shift in tectonic dynamics may explain the increase in oxygen levels.

"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," Tim Lenton, a professor at the University of Exeter's Global Systems Institute, said in a news release. "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."

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Some 550 million years ago, as the supercontinent Gondwana coalesced, the collision of continental and oceanic tectonic plates fueled the formation of a chain of volcanoes stretching thousands of miles long. The uptick in volcanic activity enabled the degassing of carbon dioxide from ancient sedimentary rocks.

According to the new study, published this week in the journal Nature Communications, as volcanoes released increasing levels of CO2 into the atmosphere, the planet warmed. Higher temperatures accelerated the weathering of continental rocks, leaching phosphorus into Earth's oceans. The nutrient fertilized photosynthesizing microbes, which released growing levels of oxygen.

Scientists designed a sophisticated biogeochemical model to confirm the plausibility of the chain of events. The simulations predicted the rise in oxygen levels as a result of increased volcanic activity. The oxygen increase predicted by the model was sufficient to explain the rise in biodiversity.

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"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," said former Exeter grad student Josh Williams, now working toward his PhD at the University of Edinburgh.

"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" added Lenton.

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