Interior of earth,geography class 7, detailed notes PDF Download

Interior of the earth

• Earth is made up of several concentric layers with one inside another.
• Radius of earth = 6871 km
• There are three layers of earth:
• Crust = 1.1%
• Mantle = 84%
• Core = 15%

CRUST:

• The upper most layer of the earths surface is called the crust.
• It is the thinnest of all the layers.
• Continental mass : 35km thick and ocean floors: 5km
• The main mineral constituent of the continental mass – silica and alumina. Thus it is called SIAL (SI-silica and AL- alumina)
• The oceanic crust mainly consist of silica and magnesium. Thus, it is called SIMA ( SI – silica and MA- magnesium)

MANTLE:

• It is located beneath the crust. It is located beneath the crust. It extends upto a depth of 2900 km below the crust.

CORE:

• It is the innermost layer with a radius of 3500 km.
• It is mainly made up of nickel and iron (ferrous) and is called nife (ni-nickel and fe-ferrous).
• The centrl core has very high temperature and pressure.

ROCKS AND MINERALS

• Rocks:
• Any natural mass of mineral matter that makes up the earths crust is called  a rock.
• Rocks are composed of different minerals which are naturally occurring substances which have certain physical properties and defenite chemical composition

Classification of rocks:

• Igneous rocks: (in latin igneious means fire)
• When the molten magma cools,it becomes solid and are called igneous rocks.
• Also called as primary rocks.
• There are two types of igneous  rocks:
• Extrusive igneous rocks:
• When the molten lava comes on the earth surface, it becomes solidby rapid cooling on the crust.these rocks are called extrusive igneous rocks.
• Also known as volcanic rocks.
• They have a free fine grained structure and are smooth and crystalline.
• Example: basalt(deccan pleateu)
• Intrusive igneous rocks:
• When the molten magma cools down deep inside the earths crust giving formation of solid rocks called intrusive igneous rocks.
• since they cool down slowly they form large grains.
• Example: granite(grinding stones )
• Sedimentary rocks (in latin sedimentum means settle down)
• When rocks roll down, crack and heat each other due to which they are broken down into small fragments called sediments.
• These sediments are transported and deposited by winds, water etc. These loose sediments are compressed and hardened to form layer of rocks. These type of rocks are called sedimentary rocks.
• Sedimentary rocks may also contain fossils (remains of dead plants and animals trapped in the layers of rocks) of plant, animal and other microbes that once lived on them.
• Example: sandstone
• Metamorphic rocks ( in Greek metamorphose means change of form)
• Under great heat and pressure, igneous and sedimentary rocks can change into metamorphic rocks.
• These change in igneous or sedimentary rocks is a process called metamorphism.
• Example: clay changing to slate and limestone into marble.

Usefulness of rocks:

Rocks are very important and provide us with

• Material for construction purposes.
• Precious stones like gold and silver.
• Mineral for various industries.
• Chemicals for medicines and fertilizer industry.
• Fuel like crude oil and coal.

Rock cycle:

The process of transformation of the rock from one form to another is known as the rock cycle.

• When the molten magma cools, it solidifies to become igneous rocks.
• The igneous rocks are broken down into small particles that are transported and deposited to form sedimentary rocks.
• When the igneous and sedimentary rocks are subjected to heat and pressre these change into metamorphic rocks.
• The metamorphic rocks which are still under great heat and pressure melt down to formmolten magma.
• These molten magma again can cooled down and solidify into igneous rocks.

Minerals: minerals are naturally occurring substances which have certain physical properties and defenite chemical composition.

Example: coal, natural gas, petroleum, gold, iron etc.