1. What is the crust?
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.
2. What are the main constituents of the continental mass?
The main mineral constituents of the continental mass are silica and alumina. It is thus called sial (si - silica and al - alumina).
3. What are the main constituents of the oceanic crust?
The oceanic crust mainly consists of silica and magnesium. It is therefore called sima. (si - silica and ma - magnesium).
4. What is mantle?
Just below the crust is the mantle which extends up to a depth of 2,900 km below the crust.
5. What is core?
The innermost layer of the earth is core with a radius of 3,500 km. It is mainly made of nickel and iron and is called nife. (ni -nickel and fe - ferrous, i.e. iron) The central core has very high temperature and pressure.
6. What are rocks ?
Any natural mass of mineral matter that makes up the earth’s crust is called a rock igneous rocks. They are also called primary rocks.
7. Name the three types of rocks.
The three types of rocks are (i) igneous rocks (ii) sedimentary rocks (iii) metamorphic rocks.
8. What are igneous rocks?
When the molten magma cools down, it becomes solid. Rocks formed over here are called igneous rocks. They are also called primary rocks.
9. What are sediments?
Rocks roll down, crack and hit each other and are broken into small fragments. These smaller particles are called sediments.
10. What are metamorphic rocks? Give example.
Igneous and sedimentary rocks can change into metamorphic rocks under great heat and pressure. For example, clay changes into slate and limestone into marble.
11. What are minerals ?
The naturally occurring substances which have certain physical properties and definite chemical composition are called minerals .e.g., uranium, gold coal, natural gas.