■ THE CRUST
◇ The crust is the outermost layer of the earth making up 0.5-1.0 percent of the earth’s volume and less than 1 per cent of Earth’s mass.
◇ Density increases with depth, and the average density is about 2.7 g/cm3 (the average density of the earth is 5.51 g/cm³).
◇ The thickness of the crust varies in the range of 5-30 km in the case of the oceanic crust and as 50- 70 km in case of the continental crust.
◇ The continental crust can be thicker than 70 km in the areas of major mountain systems. It is as much as 70-100 km thick in the Himalayan region.
◇ The temperature of the crust increases with depth, reaching values typically in the range from about 200 °C to 400 °C at the boundary with the underlying mantle.
◇ The temperature increases by as much as 30 °C for every kilometer in the upper part of the crust.
◇ Outer covering of the crust is of sedimentary material and below that lie crystalline, igneous and metamorphic rocks which are acidic in nature.
