First explosion of life on Earth left traces deep in the Earth’s mantle

(ORDO NEWS) — The Cambrian explosion – about 541 million years ago – was the beginning of the emergence of life and organisms on planet Earth. Now a new study has revealed how this explosion of life left traces deep in the Earth’s mantle.

For scientists, this shows the relationship between the Earth’s surface and what lies below it, as sediments with organic material go underground over vast geologic time as a result of subduction.

The new study looks at rare, diamond-filled volcanic rocks called kimberlites. When they are pushed to the surface, they tell us about what is going on deep in the mantle. The researchers measured the composition of carbon in 144 samples taken from 60 locations around the world.

Among geologists, the prevailing opinion is that the composition of the carbon contained in diamonds does not undergo significant changes over huge periods of time, estimated at hundreds of millions of years.

Here, however, the researchers found a shift in the ratios of certain carbon isotopes about 250 million years ago, around the time when sedimentary rocks from the Cambrian explosion should have been folded into the mantle.

This shift is potentially caused by huge changes in the carbon cycle at a time when the biosphere was increasing in mass and diversity.

“These observations show that biogeochemical processes at the Earth’s surface have a profound effect on the deep mantle, revealing an inextricable link between deep and shallow carbon cycles,” the researchers wrote.

This relationship between the carbon cycle near the surface and deep underground is not easy to measure, and, indeed, it has changed significantly over the billions of years of the Earth’s existence, rather than remained unchanged.

However, it seems clear that the dead creatures trapped in sedimentary rocks entered the mantle through plate tectonics. Their carbon remains are mixed with other materials and then brought back to the surface by events such as volcanic eruptions.

The connection was confirmed by further observations of the content of strontium and hafnium in the samples. They matched the carbon pattern, narrowing down the possibilities for how the compositions of these rocks were altered.

“This means that the carbon signature cannot be explained by other processes, such as degassing, because otherwise strontium and hafnium isotopes would not correlate with carbon isotopes,” says geochemist Andrea Giuliani of the Zurich Institute of Technology in Switzerland.

Technically, we are dealing with a sedimentary subduction flow, and these details of the carbon cycle are important for understanding what is happening on our planet – especially in the context of the ongoing climate crisis.

New research continues to uncover more and more details about how carbon is taken from the atmosphere and thrown back into it, especially as the tectonic plates that make up the planet’s surface are continuously recycled.

Scientists know that a relatively small amount of sediment penetrates deep into the mantle through subduction zones, which means that traces of the Cambrian explosion must have taken a direct path into the depths of the mantle.

“This confirms that subducted rock material in the Earth’s mantle is not uniformly distributed, but moves along certain trajectories,” says Giuliani. “The earth is indeed a complex overall system. And now we want to understand this system in more detail.”

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