Inside Our Earth

The three layers of the Earth are, the crust, the mantle and the core.

(i) Crust: The crust is the outer layer of the earth. It is the solid rock layer upon which we live.

(ii) Mantle: The mantle is made up of semi-molten rock called magma.

(iii) Core: Core is in the center and is the hottest part of the Earth. It is basically like the engine of Earth.

The rate at which magma cools determines whether an igneous rock is intrusive or extrusive.

Extrusive rocks are formed when the molten lava present inside the Earth’s interior comes out during volcanic eruption. As the lava reaches the earth, also called magma, it cools down and solidifies. This solidified magma forms extrusive rocks.

When the molten magma cools down deep inside the earth’s crust then the solid rocks so formed are called intrusive rocks.

A rock refers to any natural mass of mineral matter that makes up the Earth’s crust. Rocks can be of different types having different sizes, shapes and colours.

Igneous, sedimentary and metamorphic rocks are the three types of rocks.

(i) Igneous Rocks: These rocks are formed when magma (molten rock deep within the earth) cools and hardens.

(ii) Sedimentary Rocks: These rocks are formed from particles of sand, shells, pebbles, and other fragments of material.

(iii) Metamorphic Rocks: Metamorphic rocks are formed under the surface of the earth due to the changes from increased pressure and temperature.

Some of the uses of rocks are as follows:

(i) To build houses and buildings

(ii) Precious rocks, called gemstones, are often used to make jewellery

(iii) To make tools for cutting and drilling purposes

(iv) The fossilized remains of plants and animals present in rocks help in scientific research.

(v) The different minerals that make up different rocks are extracted and can be used as fuels, medicines, fertilizers, and industries.

Metamorphic rocks are the rocks that are formed from igneous rocks and sedimentary rocks, under great heat and pressure. For example, under extreme heat and pressure clay transforms to slate and limestone gets transformed to marble.

Igneous rocks are formed by solidification of volcanic magma.

Mantle is the middle layer and crust is the outermost layer of the earth.

Rocks contain minerals. Fossils are the substances that are formed by dead remains of organic or inorganic matter.

These rocks are formed by the deposition of sediments that trap fossils in them.

Mantle and core are the inner layers of the earth that are thicker than the crust.

(i) Core (e) Innermost layer

Core is the innermost layer of the earth.

(ii) Minerals (d) Has definite chemical composition

Minerals are naturally occurring substances which have certain physical properties and definite chemical composition.

(iii) Rocks (b) Used for roads and buildings

Rocks are commonly used for the construction of roads and buildings.

(iv) Clay (f) Changes into slate

Under great heat and pressure, clay transforms to slate (a metamorphic rock).

(v) Sail (a) Earth’s surface

Sail is composed of silica and alumina that is found on the surface of the earth.

The centre of the earth is also called the core. It is the deepest layer of the earth hat is characterized by extremely high temperature and pressure. It consists of molten magma at earth’s centre that is so hot that it can melt anything that comes in its way. Thus, we cannot go to the centre of the earth.

Under heat or pressure bigger rocks break down into very smaller pieces. These pieces of rocks get accumulated one layer over the other, called sediments. As the pressure on the layers increase they get compressed and the sediments transform to form sedimentary rocks. The silt carried by rivers gets accumulated one layer over the other and forms sedimentary rocks over a span of years.

Marble is a metamorphic rock that is formed from limestone, which is a sedimentary rock. Under extreme heat and pressure limestone gets converted into marble.

Some more objects that are made of different minerals are utensils, decorative items and jewellery.

Answers may vary.