Additional - Question:
Que: What is called the uppermost layer of the earth?
Ans: It is called the crust.
Que: What is the special feature of this layer?
Ans: It is the thinnest of all the layers
Que: Name the main mineral constituent of the continental mass.
Ans: Silica and alumina
Que: Name the constituents of the oceanic crust.
Ans: Silica and magnesium.
Que: What is the radius of the core?
Ans: The radius of the core is about 3500 km.
Que: What are the main constituents of the core?
Ans: The main constituents of the core are nickel and iron. It is usually known as nife.
Que: What is the earth’s crust made of?
Ans: It is made up of different types of rocks.
Que: What are called igneous rocks?
Ans: When the molten magma cools, it becomes solid. Rocks formed in this way are called igneous rocks.
Que: What are fossils?
Ans: The remains of the dead plant and animals trapped in the layers of rocks are called fossils.
Que: What happens when igneous and sedimentary rocks go under great heat and pressure?
Ans: They change into metamorphic rocks.
Que: What are minerals? How are they useful for mankind?
Ans: Minerals are naturally occurring substances which have certain physical properties and definite chemical composition.
Minerals are very useful for mankind. Some minerals like coal, natural gas and petroleum are used as fuels. They are also used in industries. Iron, aluminium, gold, uranium etc. are used in medicine, in Fertilizers, etc.
Que: Mention various types of rocks.
Ans: Rocks are of the three types:
1. Igneous rocks
- Sedimentary rocks
- Metamorphic rocks
- Igneous rocks, When the molten magma cools, it becomes soild. Rocks formed in this way are called igneous rocks.
- They are also called primary rocks. They are of two types - intrusive rocks and extrusive rocks.
2. Extrusive ocks. When molten lava comes on the earth's surface, it rapidly cools sown and becomes solid. Rocks formed in this way on the crust Eire called extrusive igneous rocks. For example, example, basalt.
3. Intrusive rocks. sometimes the molten magama cools deep inside the earh's crust. Solid rocks so formed are called intrusive igneous rocks. Since they cool down slowly they large grains. For examples, granite.
4. Sedimentary rocks, Small gragments of rocks are called sediments. These sediments are transported and deposited by wind, water, etc. These loose sediments are compressed and hardened to form sedimentary rocks. For example, sandstone is made from granis of sand.
5. Metamorphic rocks. When igneous and sedimentary rocks Eire subjected to great heat and pressure they chsmge into metamorphic rocks. For example, clay changes into slate and limestone into marble.
Que: What do you know about the interior of the earth?
Ans: Our earth is made up of several concentric layers with one inside another. These layers are three in number—crust, mantle smd core.
Crust. It is the uppermost layer over the earth’s surface. It is the thinnest of all the layers. It is about 35 km on the continential masses and only 5 km on the ocean floors.
The continental masses are made up of silica and alumina. It is thus called sial (si-silica and al-alumina). The oceanic crust mainly consists of silica and magnesium. It is thus called sima (si-silica and ma-magnesium).
Mantle:It is just beneath the crust. It extends up to a depth of 2900 km below the crust
Core: It is the innermost layer. Its radius is about 3500 km. It is mainly made up of nickel and iron and is known as nife (ni-nickel and fe-ferrous, Le., iron). The central core has a very high temperature and pressure.
