Ch – 2 Inside Our Earth

Important Notes:

  • The earth is made up of several concentric layers.
  • The uppermost layer of earth’s surface is known as crust. It is the thinnest layer and has a thickness of 35 km on continental mass and 5 km on ocean floors.
  • Mineral constituents of continental mass – silica and alumina (sial)
  • Mineral constituents of oceanic floor – silica and magnesium (sima)
  • Mantle is found beneath the crust.
  • Mantle extends up to a depth of 2900 km.
  • The innermost layer of the earth is core.
  • The core has a radius of about 3500 km.
  • Core is made up of nickel and iron (nife).
  • Any natural mass of mineral matter that makes up the earth’s crust is called a rock.
  • Rocks can be classified on the basis of color, texture and size.
  • There are mainly three types of rocks :
    • Igneous:
    • When the molten magma cools, it becomes solid and thus forms an igneous rock.
    • They are also known as primary rocks.
    • When the magma cools down on the surface of earth and forms a rock, it is known as extrusive igneous rock. Eg: Basalt
    • When the magma cools inside the earth and forms a rock, it is known as intrusive igneous rock. Eg: Granite
    • Deccan plateau is made up of basalt.
    • Sedimentary:
    • When rocks roll down, crack and hit each other and are broken down into small fragments, those smaller particles are called sediments.
    • The loose sediments are compressed and hardened to form layers of rock, which are known as sedimentary rocks. Eg: sandstone
    • These rocks contain fossils of plants, animals and microorganisms.
    • Metamorphic:
    • Under great heat and pressure, the igneous and sedimentary rocks change into metamorphic rocks.
    • Eg: Clay changes into slate, limestone changes into marble.
  • The process of transformation of the rock from one to another is known as rock cycle.
  • Minerals are naturally occurring substances which have certain physical properties and definite chemical composition.
  • Rocks are formed of different minerals.

Published by Priya Prakash

In the midst of winter, i found there was within me an invincible summer ~ Albert Camus

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