This chapter explores what lies beneath the Earth’s surface, starting with its internal structure. The Earth is made up of different layers: the crust, the mantle, and the core. Each layer has its own characteristics and plays a role in shaping our planet. It covers rocks and minerals, which form the Earth’s crust. It explains how they are formed, their types, and their uses in daily life. Understanding these natural materials helps us see how they contribute to the world around us.
Interior of the Earth Class
Layers of the Earth
- Earth is a lively planet with changes inside and out.
- It has layers like an onion, one inside another.
- The crust is the top layer, thin and solid.
- The crust is 35 km thick on land, 5 km under oceans.
- Continental crust has silica and alumina, called sial.
- Oceanic crust has silica and magnesium, called sima.
- The crust is just 1% of Earth’s total volume.
- The mantle lies below the crust, 2900 km deep.
- The mantle makes up 84% of Earth’s volume.
- The core is the deepest layer, 3500 km in radius.
- The core is made of nickel and iron, called nife.
- The core has high heat and pressure inside.
- The core forms 15% of Earth’s volume.
- Digging to the center is impossible, needing a 6000 km hole.
Rocks and Minerals
What Are Rocks?
- Rocks are natural masses in Earth’s crust.
- They differ in color, size, and texture.
Types of Rocks
- Igneous rocks form from cooled magma.
- Extrusive igneous rocks cool fast on the surface.
- Basalt is an example, found in the Deccan plateau.
- Intrusive igneous rocks cool slowly inside Earth.
- Granite is an example, used for grinding stones.
- Sedimentary rocks come from layered sediments.
- Sandstone is an example, made from sand grains.
- Fossils can be found in sedimentary rocks.
- Metamorphic rocks form under heat and pressure.
- Slate comes from clay, marble from limestone.
Rock Cycle
- Rocks change types in a cycle.
- Magma cools into igneous rocks.
- Igneous rocks break into sediments.
- Sediments harden into sedimentary rocks.
- Heat and pressure turn them into metamorphic rocks.
- Melting makes magma again to restart the cycle.
Uses of Rocks
- Rocks build roads, houses, and buildings.
- Stones are used in games like pitthoo and stapu.
What Are Minerals?
- Minerals are natural substances with specific traits.
- They have a fixed chemical makeup.
- Rocks contain different minerals.
- Minerals like coal and petroleum are fuels.
- Iron and gold are used in industries.
- Some minerals help in medicine and fertilizers.
Questions and Answers
1. Answer the following questions.
(i) What are the three layers of the earth? The three layers of the earth are the crust, the mantle, and the core.
(ii) What is a rock? A rock is any natural mass of mineral matter that makes up the earth’s crust. Rocks can be of different colour, size, and texture.
(iii) Name three types of rocks. The three major types of rocks are igneous rocks, sedimentary rocks, and metamorphic rocks.
(iv) How are extrusive and intrusive rocks formed? Extrusive igneous rocks are formed when molten lava comes out from the interior of the earth onto its surface. It rapidly cools down and becomes solid, resulting in a very fine-grained structure. Basalt is an example. Intrusive igneous rocks are formed when molten magma cools down deep inside the earth’s crust. Because they cool down slowly, they form large grains. Granite is an example.
(v) What do you mean by a rock cycle? The rock cycle is the process of transformation of rock from one type to another in a cyclic manner. Molten magma cools and solidifies to become igneous rock. These igneous rocks are broken down into small particles that are transported and deposited to form sedimentary rocks. When igneous and sedimentary rocks are subjected to heat and pressure, they change into metamorphic rocks. Metamorphic rocks under great heat and pressure melt down to form molten magma again, which can then cool and solidify into igneous rocks.
(vi) What are the uses of rocks? Hard rocks are used for making roads, houses, and buildings. Stones are also used in many games like seven stones (pitthoo), hop-scotch (stapu/kit kit), and five stones (gitti).
(vii) What are metamorphic rocks? Metamorphic rocks are formed when igneous and sedimentary rocks change under great heat and pressure. For example, clay changes into slate, and limestone into marble.
2. Tick the correct answer.
(i) The rock which is made up of molten magma is (a) Igneous
(ii) The innermost layer of the earth is (b) Core
(iii) Gold, petroleum and coal are examples of (b) Minerals
(iv) Rocks which contain fossils are (a) Sedimentary rocks
(v) The thinnest layer of the earth is (a) Crust
3. Match the following.
(i) Core – (e) Innermost layer (ii) Minerals – (d) Has definite chemical composition (iii) Rocks – (b) Used for roads and buildings (iv) Clay – (f) Changes into slate (v) Sial – (c) Made of silicon and alumina
4. Give reasons.
(i) We cannot go to the centre of the earth. Reaching the center of the earth is not possible because it would require digging a hole about 6000 km deep on the ocean floor, which is far beyond the depth of the deepest mine (about 4 km) and the deepest hole dug for oil (about 6 km). Additionally, the central core has very high temperature and pressure, making it extremely challenging to reach and explore.
(ii) Sedimentary rocks are formed from sediments. When rocks roll down, crack, and break into small fragments, these smaller particles are called sediments. These sediments are transported and deposited by agents like wind and water. Over time, these loose sediments are compressed and hardened to form layers of sedimentary rocks.
(iii) Limestone is changed into marble. Limestone is a type of rock that, when subjected to great heat and pressure, undergoes a process of change and transforms into marble. This transformation results in the formation of a metamorphic rock.
5. For fun.
(i) What are the minerals most commonly used in the following objects?
- Karhai: Commonly made of iron or steel (which contains iron and other minerals). [Information outside of sources]
- Ornaments: Often made of precious metals like gold and silver, as well as gemstones which are various types of minerals (e.g., diamond, ruby, sapphire) [11, Information outside of sources].
- Pan/Tava: Frequently made of iron, aluminum, or steel. [Information outside of sources]
- Bell: Traditionally made of bronze, an alloy of copper and tin. [Information outside of sources]
- Hammer: The head is typically made of steel (an alloy of iron and carbon). [Information outside of sources]
- Lamp: Older lamps might have used clay for the base. Electric lamps use various metals (like copper for wiring) and glass (made from silica) or plastics (derived from petroleum) for other parts. [Information outside of sources, 11]
(ii) Identify some more objects made up of different minerals.
- Grinding stones are made of granite, which is composed of several minerals like quartz, feldspar, and mica.
- Roads are constructed using hard rocks such as granite, basalt, and limestone, which are made up of various minerals.
- Buildings are also built using hard rocks like granite, sandstone (composed mainly of quartz), and marble (metamorphosed limestone, composed mainly of calcite, a mineral).
- Fertilisers contain various minerals like nitrogen, phosphorus, and potassium compounds [11, Information outside of sources].
- Jewelry includes items made of gold, silver, platinum, diamonds, rubies, sapphires, and other gemstones (minerals) [11, Information outside of sources].
- Coins are made of various metal alloys which are combinations of different metals (minerals) like copper, nickel, and zinc [Information outside of sources].
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