COMPOSITION AND STRUCTURE OF THE EARTH
The Earth is the third planet in the solar system and is about 4600 billion years old. Over 65% of the surface is covered in water, the remainder broken up into five continental land masses.
The Earth rotates in an anti clockwise direction about an axis tilted over at 23.5o . The Earth is an oblate spheroid, flattened at the poles and bulging at equator.
CHEMICAL COMPOSITION
crust. The outermost rock layer, divided into continental and oceanic crust. The continental crust is 25-90 km thick and is mostly granite and andesite. The oceanic crust is 6-11 km thick and mostly basalt.
mantle. The mantle stretches from the below the crust to 2900 km below the surface. The upper part is partially molten and the lower part is very dense. The main mantle rock is peridotite.
core. The core is about 7000 km in diameter with a temperature of 6000oC and a pressure of over 3 million atmospheres. The inner core is a lumpy solid iron sphere and the outer core is a thick liquid iron layer.
PHYSICAL STRUCTURE
lithosphere. Equivalent in part to the crust, the lithosphere comprises of a number of tectonic plates that 'float' on the asthenosphere.
asthenosphere. Ductile rocks that lie from below the lithosphere to 250 km below the surface.
mesosphere. Solid rocks below the asthenosphere.
