Inside Our Earth

              Interior of the earth

The uppermost layer over the earth's surface is called the crust . It is the thinnest of all the layers.It is about 35 Km.on the continental masses and only 5 Km. on the ocean floors.

The main mineral Constituents of the continental mass are silica and alumina.It is thus called sial { Si - silica and Al - Alumina }

The oceanic crust mainly consists of silica and magnesium , it is therefore called Sima { Si - silica and Ma - magnesium } just beneath the crust is the mantle which extends up to a depth of 2900 Km.below the crust.

The innermost layer is the core with a radius of about 3500 Km .

It is mainly made up of nickel and Iron and is called nife { ni - nickle and fe - ferros that is Iron}

{ The deepest mine in the world is  South Africa In search for oil engineers have dug a hole about 6000 Km deep.}

                 

          Rocks and Minerals

The earth's crust is made up of various types of rocks.Any natural mass of mineral matter that makes up the earths crust is called a rock.Rocks can be of diffrent colour , size and texture.

There are three major types of rocks: igneous rocks, sedimentary  rocks{Ex- sandstone is made from grains of sand.these rocks may also contain fossils of plants,animals and other micro-organisms that once lived on them} and metamorphic rocks{Ex- clay changes into slate and limestone into marble}.

When the molten magma cools , it becomes solid. Rocks thus formed are called igneous rocks. They are also called primary rocks . There are two types of igneous rocks: intrusive rocks { Ex- Granite }and extrusive rocks{ Ex- Basalt.The Deccan plateau is made up of basalt rocks } .

Can you imagine lava coming out from the volcanoes? Lava is actually fiery red molten magma coming out from the interior of the earth on its surface.When this molten lava comes on the earth's surface, it rapidly cools down and becomes solid .Rocks formed in such a way on the crust are called Extrusive igneous rocks.Sometimes the molten magma cools down deep inside the earth's crust. Solid rocks so formed are called intrusive igneous rocks.

You will be surprised to know that one type of rock changes to another type under certain conditions in a cyclic manner. This process of transformation of the rock from one to another is known as the rock cycle . When the molten magma cools; it solidifies to become igneous rock.These 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 pressure they change into metamorphic rocks.The metamorphic rocks which are still under great heat and pressure melt down to form molten magma.

This molten magma again can cool down and solidify into igneous rock.