New research has brought us closer to understanding the composition of the earth’s interior – and it is less uniform than previously thought.
The mantle is the layer of Earth that comprises the bulk of Earth’s volume, located below the outer crust we live on. The chemical characteristics of the mantle can help us understand the earth’s volcanic activity as well as the cycling of important materials and gases, including CO2.
“Something that people probably don’t realize is volcanism that we do not see—volcanism that happens below the sea level—represents more than 80% of the volcanism on earth. If we want to understand how earth is working in general, we really need to understand how this type of volcanism works,” said Sarah Lambart, assistant professor in the department of geology and geophysics at the University of Utah.
Despite its importance, Lambart said the chemical composition of the mantle is not well understood. Because the mantle is so far beneath the Earth’s surface, geologists have previously used volcanic rocks originating as magma in the mantle to understand its composition, but the melting and mixing that occurs as the magma moves up to Earth’s surface alters its original chemistry.
To avoid these challenges, Lambart and her colleagues looked at samples from mantle cumulate, which represent the first minerals to crystallize. They discovered that the mantle chemical composition is a lot more heterogeneous than previously thought. Lambart compared the mantle’s mineral structure to paintings by the abstract expressionist Jackson Pollock.
“When you look at a Pollock painting from far away, it looks really like a mess actually, but when you look at it in detail, it is what I would call an organized mess, and I think that is what represents the mantle the best” said Lambart.