Important Questions: Inside Our Earth | Social Studies (SST) Class 7 (Old NCERT) PDF Download

Q1: How are minerals useful to mankind?
Ans: Minerals are essential to humankind in various ways:

• Some serve as fuels, such as coal, natural gas, and petroleum.
• They are vital in industries, providing materials like iron, aluminium, gold, and uranium.
• Minerals are used in medicine and in the production of fertilisers.

Q2: What are the uses of rocks?
Ans: Uses of rocks

• The hard rocks are used for making roads, houses, and buildings.
• Stones are used in many games. For example, seven stones (pitthoo), hopscotch (stapu/kit kit), five stones (gitti).

Q3: How are extrusive and intrusive rocks formed?
Ans: Extrusive rocks: These rocks form when molten lava erupts onto the Earth's surface. They cool quickly, resulting in a fine-grained structure. An example of extrusive igneous rock is basalt, which makes up the Deccan Plateau. 
Intrusive rocks: These rocks develop when molten magma cools slowly beneath the Earth's crust. This slow cooling allows for larger crystals to form. A common example of intrusive igneous rock is granite, often used for grinding stones.

Q4: Sedimentary rocks are formed from sediments. Give reason.
Ans: Rocks roll down, crack, and hit each other and are broken down into small fragments. These smaller particles are called sediments. These sediments are transported and deposited by wind, water, etc. These loose sediments are compressed and hardened to form layers of rocks. These types of rocks are called sedimentary rocks.

Q5: What do you know about Earth’s interior?
Ans: The earth is made up of several concentric layers with one inside another.

• 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.
• Mantle: Just beneath the crust is the mantle which extends up to a depth of 2900 km. below the crust.
• Core: 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. The central core has very high temperature and pressure.

Q6: Write a note on various types of rocks?
Ans: There are three major types of rocks: igneous rocks, sedimentary rocks and metamorphic rocks.
Igneous rocks: These rocks form when molten magma cools and solidifies. They are also known as primary rocks and can be classified into two types:

• Extrusive igneous rocks: These form when lava erupts onto the Earth's surface and cools quickly, resulting in fine-grained rocks like basalt.
• Intrusive igneous rocks: These form when magma cools slowly beneath the Earth’s surface, leading to coarse-grained rocks like granite.

Sedimentary rocks: These rocks are created from the accumulation and compression of sediments, which are small fragments of other rocks. Sediments are transported by wind and water. An example is sandstone, formed from sand grains. Metamorphic rocks: These rocks arise when igneous or sedimentary rocks change due to extreme heat and pressure. For instance, clay can transform into slate, and limestone can change into marble.
Metamorphic rocks: Igneous and sedimentary rocks can change into metamorphic rocks under great heat and pressure. For example, clay changes into slate and limestone into marble.

Q7: Distinguish between crust and core.
Ans: The Earth's structure consists of different layers, primarily the crust and the core.
Crust:

• The outermost layer of the Earth.
• Thickness varies: about 35 km under continents and 5 km under oceans.
• Composed mainly of silica and alumina in continental areas (referred to as sial).
• Oceanic crust is primarily made of silica and magnesium (known as sima).
  

Core:

• The innermost layer of the Earth, with a radius of about 3,500 km.
• Composed mainly of nickel and iron (often called nife).
• Divided into two parts: the outer core (liquid) and the inner core (solid).
• Characterised by extremely high temperatures and pressures.