Effect of pressure on physical phenomena in the crust

The physical properties of materials as tabulated in handbooks and as used in our everyday life refer to measurements made in the environment which surrounds us, namely at atmospheric pressure (slightly more than one bar at sea level). If we were able to move down into the interior of the Earth with our testing equipment we would find the environmental pressure increasing at a rate of about 30,000 bars for each 100 km of descent. We would find, moreover, that under these conditions our testing apparatus would record very different physical behavior from that which might be anticipated from observations made at the surface under our normal atmospheric environment.