Earth’s fiery interior is ‘swallowing up’ more carbon than thought

Scientists previously believed carbon subducted into the Earth’s mantle largely re-emerged through volcanoes

Harry Cockburn
Environment Correspondent
Wednesday 28 July 2021 10:41 BST
Volcano's spectacular eruption

The tectonic plates that make up the Earth’s crust are in perpetual slow motion – colliding, pulling apart, or rubbing past one another in a slow dance of creation and destruction on an epic scale.

But new research has revealed that these huge geological movements — which we feel as earthquakes and whose power we see as volcanoes, tsunamis, mountains or trenches — actually play a role in sequestering carbon.

Scientists from Cambridge University and Nanyang Technological University in Singapore have found the collisions of tectonic plates drag more carbon into the Earth’s interior than previously thought.

Their research has revealed that the carbon drawn into Earth’s interior at subduction zones – where tectonic plates collide and dive into our planet’s super-heated interior – tends to stay locked away at depth, rather than then resurfacing in the form of volcanic emissions.

The study suggests only about a third of the carbon recycled beneath volcanic chains returns to the surface via recycling, in contrast to previous theories that what goes down mostly comes back up.

This could have implications for understanding the climate crisis we face today.

One of the solutions for tackling the environment emergency caused by runaway greenhouse gas emissions is to find ways to reduce the amount of CO2 in Earth’s atmosphere.

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By studying how carbon behaves in the “deep Earth”, which houses the majority of our planet’s carbon, scientists can better understand the entire lifecycle of carbon on Earth, and how it flows between the atmosphere, oceans and life at the surface.

Currently, the most closely studied parts of our planet’s carbon cycle are the processes occurring at or near the Earth’s surface.

However, deep carbon stores also play a key role in maintaining the habitability of our planet by regulating atmospheric CO2 levels, the scientists said.

"We currently have a relatively good understanding of the surface reservoirs of carbon and the fluxes between them, but know much less about Earth’s interior carbon stores, which cycle carbon over millions of years," said lead author Stefan Farsang, who conducted the research at Cambridge’s Department of Earth Sciences.

There are a number of ways for carbon to be released into the Earth’s atmosphere as CO2, but there is only one path in which it can return to the Earth’s interior: via the slow process of plate subduction.

When this occurs, surface carbon, for instance in the form of seashells and micro-organisms which have locked atmospheric CO2 into their shells, is gobbled up into the Earth’s mantle.

Scientists had thought that much of this carbon was then returned to the atmosphere as CO2 via emissions from volcanoes. But the new study reveals that chemical reactions taking place in rocks swallowed up at subduction zones trap carbon and send it deeper into Earth’s interior, thereby stopping some of it coming back to Earth’s surface.

The research is published in the journal Nature Communications.

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