Chapter 2. Inside our Earth

Interior of Earth
• earth is made up of several concentric layers with one layer inside another layer. radius of earth is 6371 km.

• uppermost layer of earth’s surface is known as crust. This is thinnest of all layers. This is about 35 km on continental masses and 5 km on ocean floor.
• continental mass constitute of silica and alumina. This is thus known as sial [si-silica and al-alumina].
• oceanic crust mainly made up of silica and magnesium; it is therefore known as sima [si-silica and ma-magnesium].
• crust forms only 1% of volume of earth, 84% consists of mantle and 15% makes core.

• Mantle layer is exist just beneath earth’s crust which extends up to a depth of 2900 km below crust.

• innermost layer is core with a radius of about 3500 km. This is mainly made up of nickel and iron and is known as nife [ni – nickel and fe – ferrous i.e. iron].
• central core has very high temperature and pressure.

Rocks and Minerals
• Any natural mass of mineral matter that makes up earth’s crust is known as a rock.
• There are three major types of rocks: Igneous Rocks, Sedimentary Rocks and Metamorphic Rocks.
• When molten magma cools, it becomes solid. Rocks thus formed are known as igneous rocks. They are known as primary rocks.

Igneous Rocks
• There are two types of igneous rocks: intrusive rocks and extrusive rocks.
(1) Intrusive igneous rocks: When molten magma cools down deep inside earth’s crust and forms solid rocks example- Granite rock.
(2) Extrusive igneous rocks: Rock formed by cooling of molten lava on surface which comes out from interior of earth. They have a very fine grained structure example- basalt rocks.

Sedimentary Rocks
• Sediments are smaller particles formed by rolling down of rocks, developing cracks in rocks and being hit by other rocks.
• Sediments are transported and deposited by some agents [wind, water.] & slowly sediments are compressed and hardened to form layers of rocks.
• These types of rocks are known as sedimentary rocks. For example, sandstone is made from grains of sand.
• These rocks may contain fossils of plants, animals & other microorganisms that once lived on them.

Metamorphic Rocks
• Igneous and sedimentary rocks can change into metamorphic rocks under great heat and pressure i.e. clay changes into slate and limestone into marble.
• process of transformation of rock from one to another is called rock cycle.

Minerals and Rocks
• Minerals are naturally occurring substances that have certain physical properties and definite chemical compositions. Rocks are made up of different minerals.
• Minerals are very important to humankind. Some are used as fuels i.e. coal, natural gas and petroleum. They are used in industries – iron, aluminium, gold, uranium, in medicine, in fertilisers.

Note: deepest mine in world, is in South Africa. This is about 4 km deep. In search of oil, engineers dug a hole of about 6 km deep.

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