Earth Mantle

The water content of Earth’s mantle is a key measurement of Earth’s water budget. Global recycling of water on Earth drives important forms of volcanism such as island arcs, controls the flow of upper-mantle fluid and plays a role in the evolution of mantle plumes.

Hydrogen is the most abundant element in the solar system. There are various configurations of hydrogen on Earth. Hydrogen exists as water vapor in the atmosphere, and water and ice in the ocean and land water, fluids in the magma and volcanoes, minerals in the crust and mantle, and with metallic iron in the core.

Hydrogen and water are important in the dynamics of Earth’s interior. They lower the internal friction of rocks and cause earthquakes. Also, water generates magmas by lowering the melting temperature of silicates in the mantle. Water softens rocks and enhances mantle convection.

While subducted oceanic crust dehydrates at shallow depth, faster and colder slabs can carry water much deeper. Average water abundance in the mantle changes substantially across the boundary between the upper mantle and the transition zone, as well as across the boundary between the transition zone and the lower mantle.The transition zone contains more than ten times more water than the upper mantle. The abundance of water in the lower mantle is unknown but is believed to hold less than the transition zone. The average abundance of chemically bound water in these different regions of Earth, as well as possible occurrences of smaller layers of water rich rock are central to our understanding of Earth’s water budget over extended geologic time. 

Carbon is not only essential to life and Earth’s habitability but also traces and modifies geological processes of subduction, partial melting, degassing and change in the composition of rocks, providing valuable insights into Earth’s evolution. 

Over the history of the planet, carbon transport between surface and deep reservoirs has impacted the atmospheric, oceanic and crustal CO2 budges together with the composition and state of the Earth’s mantle. Carbon is transported from Earth’s surface to its interior mainly as carbonate minerals in subduction zones and is returned through volcanic degassing.