Dynamic Compression of Earth Materials

Shock wave techniques have been used to investigate the pressuredensity relations of metals, silicates, and oxides over the entire range of pressures present in the earth (3.7 x 10^6 bars at the center). In many materials of geophysical interest, such as iron, wüstite, calcium oxide, and forsterite, major shock-induced phase changes dominate the compression behavior below pressures of 10^6 bars. The shock wave data for the high-pressure phases of these minerals lead to important inferences about the composition of the lower mantle and outer, liquid core of the earth. The lower mantle of the earth appears to have a slightly higher density than is inferred to correspond to the behavior of an olivine-rich assembiage of the same composition as the upper mantle. The core has a density some 10 percent less than that of pure iron and may have 9 to 12 percent sulfur or about 8 percent oxygen by weight.