ABSTRACT
The small amount of heavier elements in the solar system seems to have become concentrated in the area between the Sun and Jupiter, where it subsequently formed the inner planets: Mercury, Venus, Earth and Mars. The damage produced by earthquakes is due to the three-dimensional movement of the ground as surface waves travel out from the epicentre. The simplest way of representing a good deal of the seismic evidence available is to draw velocity profiles for the Earth showing seismic wave velocity at varying depths. The Earth probably had radio-isotopes in greater abundance in the past, and so in that sense the planet is cooling down. The loss of internally generated heat through the surface of the Earth is called heat flow. Ocean ridges and rift valleys are areas only of high heat flow, and it therefore seems likely that they lie zones in the mantle where temperatures are higher than average.
