We all know that things happening below the Earth’s crust, the top layer in which humans inhabit, impact what’s going on above. From volcanoes to tsunamis, the huge tectonic plates beneath our feet are hugely influential.
For the first time ever, scientists have discovered how life above has infiltrated the interior of our planet. According to a recent paper, published in Science Advances, the development of life on Earth impacts its lower mantle. This layer lies 660 to 2900 kilometers below the surface of the planet, between the transition zone and the outer core.
Rocks from below
A team from the Department of Earth Sciences at ETH Zurich, examined 150 samples of rare diamond-bearing volcanic rocks, named kimberlites. These samples were taken from different time periods of the lowest layer of the Earth’s mantle.
Younger kimberlites – which are less than 250 million years old – were found to significantly differ in composition to older samples. The way in which these rocks differed was in their carbon isotope content, this basically means they have a different makeup while still remaining as carbon atoms. If you want a little more information about isotopes, check out this fascinating article discussing how scientists created a new magnesium one to learn more.
How did carbon infiltrate the depths of the planet?
Researchers were intrigued by what could have caused this huge difference in makeup, so looked to the history of what was happening here on Earth to figure it out. They traced the time period back to when almost all of today’s existing animals appeared on Earth for the first time.
“The enormous increase in life forms in the oceans decisively changed what was happening on the Earth’s surface,” Andrea Giuliani explains, the researcher that led the study. “And this in turn affected the composition of sediments at the bottom of the ocean.”
It’s thought that sediment deposits of these living creatures on the ocean floor managed to squeeze their way into the mantle through the movement of the Earth’s tectonic plates. The carbon in these organisms mixed with other rocks in the mantle and slowly made their way down to great depths below. After the carbon has spent around 200-300 million years in the lower mantle, it is thought that some of it may rise again, back up to the surface in the form of magma.
Tests for other elements such as strontium and hafnium also were found to have a similar cycle as carbon. The fact these other chemicals correlated to carbon’s cycles allowed scientists to select this theory over previous ideas.
Why is this study important?
This interesting new data hugely impacts our understanding of our planet. “The Earth is really a complex overall system,” Giuliani stated. “And we now want to understand this system in more detail.” In the future, this study may give clues to how life emerged on Earth and new places to look for it.
Source study: Science Advances – Perturbation of the deep-Earth carbon cycle in response to the Cambrian Explosion