Chapter 2 – Inside Our Earth

Chapter 2 – Inside Our Earth

 

1. Interior of Our Earth

Our earth is like an onion, which is made up of many concentric layers.

 

 

1. Crust:

• • It is the uppermost and thinnest layer  of the earth.
  • It is about  35 km thick on continental mass  and only  5  km thick on the  oceanic floor.
  • Continental crust: is mainly made up of silica and alumina, hence it  is called SiAl.
  • Oceanic crust: is  mainly made up of silica and magnesium, so it  is called  SiMa.

1. Mantle:

• • Just below the crust lies the mantle, which  extends to a depth of  about 2900  km.
  • It is mainly composed of molten rocks and contains extremely hot substances.

iii.  Core:

• • The innermost layer of the mantle is the core, the radius of which is about 3500 km.
  • It is mainly made up of nickel and iron, so it  is called NiFe.
  • Inner Core: In solid state.
  •  Outer Core: In liquid state.
  • The core has very high temperatures and pressures.

 

2. Rocks and Minerals

•  Rocks: Any natural mass that forms the earth’s crust is called a rock.
  • Shells can be of different shapes, colors, and textures.
• Minerals: Rocks are made up of them.
  • Minerals are naturally occurring substances that have a definite chemical composition.
  • They are very useful to mankind (such as fuel minerals – coal, petroleum, natural gas; Iron, aluminum, gold, uranium etc.).
•  Types of Rocks:  There are mainly three types:

1. Igneous Rocks – Primary Rocks:

• • • These rocks are formed when molten magma  (inside the earth) or lava  (on the surface of the earth) cools down and becomes solid.
    •  Intrusive Igneous Rocks: When magma cools deep inside the crust and solidifies.
      • Example: Granite.
    •  Extrusive Igneous Rocks: When molten lava comes to the surface of the earth and cools rapidly to solidify.
      • Example: Basalt. The Deccan Plateau is made up of basalt shale.

1. Sedimentary Rocks:

• • • These rocks are formed when the shells break into small pieces and are transported from one place to another by wind, water, etc. and keep accumulating.
    • These loose  sediments, clenching and hardening together, form layers of rock.
    • They can often contain  fossils  of plants, animals, and other microorganisms that once lived on these rocks.
    • Example: Sandstone is formed from grains of sand. Limestone .

iii.  Metamorphic Rocks:

• • • These rocks are formed when igneous and sedimentary rocks  change their form (physique)  due to too much heat and pressure.
    • Example:  clay turns into slate; Limestone turns into  marble.

 

3. Rock Cycle

• Rock cycle is the process by which one type of rock changes from one cyclic manner to another.
• This is an ongoing process.
• Procedure:
  • Molten magma cools to form igneous rocks.
  • Igneous rocks break down into smaller particles and form sedimentary rocks.
  • Igneous and sedimentary rocks turn into metamorphic rocks under high heat and pressure.
  • Metamorphic rocks can melt again to become magma due to excessive heat and pressure, and this cycle continues.

4. Uses

• Shells are used for a variety of purposes:
  • Build roads.
  • Building houses and buildings.
  • Playing games (e.g. stooges, ballast).
  • Minerals are used in various industries and energy production.