The bulk of the Earth is made from iron, oxygen, magnesium and silicon.
• More than 80 chemical elements occur naturally in the Earth and its atmosphere.
- The crust is made mostly from oxygen and silicon, with aluminium, iron, calcium, magnesium, sodium, potassium, titanium and traces of 64 other elements.
• The upper mantle is made up of iron and magnesium silicates; the lower is silicon and magnesium sulphides and oxides.
• The core is mostly iron, with a little nickel and traces of sulphur, carbon, oxygen and potassium.
• Evidence for the Earth’s chemistry comes from analysing densities with the help of earthquake waves, and from studying stars, meteorites and other planets.
• When the Earth was still semi-molten, dense elements such as iron sank to form the core. Lighter elements such as oxygen floated up to form the crust.
• Some heavy elements, such as uranium, ended up in the crust because they easily make compounds with oxygen and silicon.
• Large blobs of elements that combine easily with sulphur, such as zinc and lead, spread through the mantle.
• Elements that combine with iron, such as gold and nickel, sank to the core.
- Earth strong magnetic field is due to its of the presence of inner Nickel-Iron core.