Most of Earth's carbon hidden in inner core

As much as two-thirds of Earth's carbon may be hidden in the inner core, making it the planet's largest carbon reservoir, according to a new model.

"This model challenges the conventional view that the Earth is highly depleted in carbon, and therefore bears on our understanding of Earth's accretion and early differentiation," the researchers noted.

Using a variety of experimental techniques to obtain sound velocities for iron carbide up to core pressures, the researchers suggested that iron carbide, Fe7C3, could be a leading component of the inner core.

"The model of a carbide inner core is compatible with existing cosmochemical, geochemical and petrological constraints, but this provocative and speculative hypothesis still requires further testing," said principal investigator of the project Jie Li, associate professor at University of Michigan.

"Should it hold up to various tests, the model would imply that as much as two-thirds of the planet's carbon is hidden in its center sphere, making it the largest reservoir of carbon on Earth," Li added.

In their study, the researchers used a variety of experimental techniques to obtain sound velocities for iron carbide up to core pressures.

They used diamond-anvil cell techniques in combination with a suite of advanced synchrotron methods including nuclear resonant inelastic X-ray scattering, synchrotron Mössbauser spectroscopy and X-ray emission spectroscopy.

The study is forthcoming in the journal Proceedings of the National Academy of Sciences.