Composition of Earth's Core: Shock-wave Experiments and Element Distribution, Slides of Geology

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Composition of the core

Shock-wave experiments show that the density of the core is too low for it being composed only of iron. An admixture of lighter elements is required, but we do not know which.

Canon de LLNL Precise measurement of the temperature of the shocked sample remains difficult One assumes that equilibrium conditions are attained One assumes that hydrostatic pressure conditions prevail Shock wave experiments

 Outer core:

Composed of Fe alloy with about 10% by weight “light” elements Ni ~4% Favored other light elements: O, S, Si, C, H

• Cosmochemical constraints + laboratory measurements +
• Theoretical mineral physics computations
• no consensus yet but rapid progress McDonough & Sun 95

Inner core: liquid->solid transition in Fe- More pure iron than outer core : Light elements expelled into outer core

Inner core composition

 Inner core:

 Composed of more pure iron, with only about 3% light elements (S, Si, C, H..)  As the inner core cristallizes (it grows with time because of the cooling of the earth), it ejects light elements into the outer core, causing convection motions in the outer core (=> dynamo).  Several possible cristalline structures: Hcp, Bcc, Fcc most likely Hcp "  The melting temperature of iron (and iron alloys with light elements) at ICB conditions is an important constraint on the temperature profile in the earth’s core and, and on the temperature gradient at the CMB