Traces of Ancient Life Discovered Deep in Earth's Mantle

Traces of ancient life have been found in rocks deep inside the Earth's mantle, having been sucked down there hundreds of millions of years ago.

Scientists discovered traces of carbon—the element on which life on Earth is based—that appear to have come from the Cambrian Explosion. The Cambrian Explosion was an unparalleled burst of evolution over 540 million years ago, during which point most major groups of animals appeared on Earth.

Before the Cambrian Explosion, life on Earth was simple and mostly single-cell or smaller multicell creatures. Afterward, new and more complex kinds of life emerged.

In a study published in Science Advances, researchers provided evidence to show that lifeforms from this time changed the chemical make-up of Earth's mantle.

Scientists looked at diamond-bearing rocks from deep inside the Earth's interior called kimberlites. They examined around 150 different samples taken from volcanic sites around the world and found major differences in the make-up of the kimberlites depending on their age.

The oldest kimberlites showed typical amounts of carbon isotopes for magma in the Earth's mantle. But this changed when scientists examined the younger kimberlite samples, which dated to around 250 million years ago. These showed variations of certain types of carbon that scientists say were likely caused by organic matter from the Cambrian Explosion.

The Cambrian Explosion mainly happened in Earth's ancient oceans. It saw the rise of many new and more complex kinds of life not seen before on the planet such as creatures with gills, hard shells, and jaws with teeth for catching prey.

Organisms that emerged during the Cambrian Explosion would have eventually filtered down to the seafloor where they would become sediment. This would eventually be drawn into Earth's mantle via subduction. Hundreds of millions of years later, this material would be transported back to the surface, some of which would become the kimberlite samples studied.

Only small amounts of sediments from the ocean floor typically make it as far as the Earth's mantle, meaning the changes made by the organic matter to the magma researchers looked at were highly significant.

"The enormous increase in life forms in the oceans decisively changed what was happening on the Earth's surface," lead author Andrea Giuliani, of the Department of Earth Sciences at ETH Zurich, said in a statement. "And this, in turn, affected the composition of sediments at the bottom of the ocean."

"The Earth is really a complex overall system. And we now want to understand this system in more detail."

Artist's impression of the early Cambrian explosion
Artist's impression of the early Cambrian explosion. Researchers said evidence of the ancient life that emerged during this period was found deep in the Earth's interior. dottedhippo/Getty Images