Interior of the Earth
- Crust- uppermost layer over the earth s surface, thinnest of all the layers, 35 km. on the continental masses and only 5 km. on the ocean floors.
- Sial- The main mineral constituents of the continental mass are silica and alumina
- Sima-The oceanic crust mainly consists of silica and magnesium
- Mantle-Just beneath the crust extends up to a depth of 2900 km below the crust.
- Nife- innermost layer, the radius of about 3500 km, mainly made up of nickel and iron. Do you know?
- The crust forms only 1 percent of the volume of the earth, 84 percent consists of the mantle and 15 percent makes the core.
- The radius of the earth is 6371 km. the central core has a very high temperature and pressure.
Try yourself:Which one of the following is the dominant element of the earth crust?
Rocks and Minerals
Three major types of rocks: igneous rocks, sedimentary rocks, and metamorphic rocks.
1. Igneous rocks
- When the molten magma cools, it becomes solid. Rocks thus formed are called igneous rocks also called primary rocks
- Two types of igneous rocks: intrusive rocks and extrusive rocks
- Extrusive igneous rocks-
- When molten lava comes on the earth’s surface, it rapidly cools down and becomes solid.
- Rocks formed in such a way on the crust.
- They are very fine-grained structure. For example, basalt
- Deccan plateau is made up of basalt rocks
➢ Intrusive igneous rocks
- When the molten magma cools down deep inside the earth’s crust, solid rocks are formed.
- Solid rocks so formed are called intrusive igneous rocks.
- Form large grains.
- Granite is an example of such a rock.
- Sediments: smaller particles of rocks
2. Sedimentary rocks
- Loose sediments are compressed and hardened to form layers of rocks, sandstone is made from grains of sand. These rocks may also contain fossils of plants, animals, and other microorganisms that once lived on them.
3. Metamorphic rocks
- Igneous and sedimentary rocks can change into metamorphic rocks under great heat and pressure.
- For example, clay changes into slate and limestone into marble.
- 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 fertilizers, etc.