1. CRUST

This is the thin outlayer of the earth - there are two types of crust:

(i) Continental Crust (lighter) - this can be up to 70km thick, it is very old rock and Granite is the most common.

(ii) Oceanic Crust (heavier / denser) - this is very young rock as new oceanic crust is created at constructive plate boundaries. Oceanic crust may be between 6-10km thick and is mainly Basalt

2. MANTLE

The top layer of the mantle is rigid whilst the rest of the mantle is semi-molten

The Crust and Mantle can be sub-divided into two main zones with distinctive physical properties.

1. The Lithosphere - the crust and upper mantle which are mainly solid

2. The Asthenosphere - this is the lower mantle and is semi-molten in nature

The mantle is mainly made up of silicate rocks (rich in magnesium and iron) - the mantle reaches a depth of up to 2900km and may reach up to 5000oC - it is here in the mantle where convection currents can be generated.

3. CORE (Outer / Inner)

Temperatures reach up to 6200oC at the centre of the core - the source of this heat is believed to be the radioactive decay of potassium, uranium and thorium. Although frictional heating also occurs by the sinking of dense iron-rich material to the core.

(i) OUTER CORE - this is in a semi-molten state

(ii) INNER CORE - this is solid (it is at very high pressure) and consists mainly of iron and nickel.

See also the following links / resources...

The "Inside the Earth" pages from the USGS

This page from the Moorland School site - also provides an excellent overview of the characteristics of the various layers of the earth.

See also this link on Structure of the Earth from Alan Parkinson's Geography Pages - this helps to explain how we know about the structure of the earth