The earth is made up of several concentric layers with one inside another.
Crust – The uppermost layer over the earth’s surface.
It is the thinnest of all the layers.
It is about 35 km. on the continental masses and only 5 km. on the ocean floors.
The main mineral constituents of the continental mass are silica and alumina. It is thus called si-al (si-silica and al-alumina)
The oceanic crust mainly consists of silica and magnesium; it is therefore called sima (si-silica and ma-magnesium)
Mantle – Just beneath the crust is the mantle which extends up to a depth of 2900 km.
Core – The innermost layer is the core with a radius of about 3500 km.
It is mainly made up of nickel and iron and is called nife (ni – nickel and fe – ferrous, i.e. iron).
The central core has a very high temperature and pressure.
Rocks and Minerals
The earth’s crust is made up of various types of rocks.
Rock- Any natural mass of mineral matter that makes up the earth’s crust.
There are three major types of rocks-
Igneous rocks-when the molten magma cools; it solidifies to become igneous rock.
Sedimentary rocks- igneous rocks are broken down into small particles that are transported and deposited to form sedimentary rocks.
Metamorphic rocks- When the igneous and sedimentary rocks are subjected to heat and pressure, they change into metamorphic rocks.
Rocks are made up of different minerals.
Minerals- are naturally occurring substances which have certain physical properties and definite chemical composition.
Minerals are very important to humankind. Some are used as fuels. For example, coal, natural gas and petroleum. They are also used in industries – iron, aluminium, gold, uranium, etc., in medicine, in fertilisers, etc.