Horizon Academy
Inside Our Earth
Important Questions & Answers
Geography - Class 7
The Earth's Interior
1. Why is the Earth called a dynamic planet?
Answer: The Earth is called a dynamic planet because it is always changing both inside and outside.
2. What is the Earth made up of?
Answer: The Earth is made up of several layers like an onion. These layers are the crust, mantle, and core.
3. How many main layers does the Earth have? Name them.
Answer: The Earth has three main layers:
- Crust
- Mantle
- Core
Crust
The outermost layer, thinnest of all layers
Mantle
Middle layer, thickest part of Earth
Core
Innermost layer, mostly iron and nickel
4. What is the crust?
Answer: The crust is the uppermost layer of the Earth. It is the thinnest layer.
5. What is the thickness of the crust?
Answer:
- On continental areas, it is about 35 km thick.
- On the ocean floor, it is only about 5 km thick.
6. What is the continental crust made of? What is it called?
Answer: The continental crust is made of silica and alumina. It is called SIAL (Si for silica, Al for alumina).
7. What is the oceanic crust made of? What is it called?
Answer: The oceanic crust is made of silica and magnesium. It is called SIMA (Si for silica, Ma for magnesium).
8. What is the mantle? Where is it located?
Answer: The mantle is the layer just below the crust. It extends up to 2900 km below the crust.
9. What is the core of the Earth?
Answer: The core is the innermost layer of the Earth. It has a radius of about 3500 km.
10. What is the core made up of? What is it called?
Answer: The core is made up of nickel and iron. It is called NIFE (Ni for nickel, Fe for iron/ferrous).
11. What is the temperature and pressure like in the core?
Answer: The core has very high temperature and pressure.
12. How deep is the deepest mine in the world?
Answer: The deepest mine is in South Africa and it is about 4 km deep.
13. How deep have engineers dug for oil?
Answer: Engineers have dug up to 6 km deep in search of oil.
14. How deep would we have to dig to reach the center of the Earth?
Answer: We would need to dig about 6000 km deep from the ocean floor to reach the center of the Earth (but it is not possible!).
15. Why is it difficult to reach the center of the Earth?
Answer: It is difficult because the depth is too much (about 6000 km), and the temperature and pressure are extremely high.
Additional Facts
1. What percentage of the Earth's volume is made up of the crust, mantle, and core?
Answer:
- Crust: 1%
- Mantle: 84%
- Core: 15%
2. What is the radius of the Earth?
Answer: The radius of the Earth is 6371 km.
Rocks and Minerals
3. What is a rock?
Answer: A rock is a natural mass of mineral matter that makes up the Earth's crust. Rocks come in different colours, sizes, and textures.
4. How many major types of rocks are there? Name them.
Answer: There are three major types of rocks:
- Igneous rocks
- Sedimentary rocks
- Metamorphic rocks
Igneous Rocks
5. How are igneous rocks formed?
Answer: Igneous rocks are formed when molten magma cools and becomes solid. They are also called primary rocks.
6. What are the two types of igneous rocks?
Answer:
- Intrusive igneous rocks
- Extrusive igneous rocks
7. What is lava?
Answer: Lava is molten magma that comes out from a volcano onto the Earth's surface.
8. What are extrusive igneous rocks? Give an example.
Answer: When lava comes out and cools down quickly on the Earth's surface, it forms extrusive igneous rocks. They have a fine-grained structure. Example: Basalt (Deccan Plateau is made of basalt)
9. What are intrusive igneous rocks? Give an example.
Answer: When molten magma cools slowly inside the Earth's crust, it forms intrusive igneous rocks. They have large grains. Example: Granite (used in grinding stones)
Sedimentary Rocks
10. How are sedimentary rocks formed?
Answer: Sedimentary rocks are formed when small rock pieces (sediments) are transported by wind or water and then compressed and hardened in layers.
11. What is a sediment?
Answer: Sediments are small pieces of rocks formed by breaking and cracking of bigger rocks.
12. Give an example of a sedimentary rock.
Answer: Sandstone, which is made from grains of sand.
13. What are fossils?
Answer: Fossils are the remains of dead plants and animals found trapped in the layers of sedimentary rocks.
e.g.: remains of dinosaur bones trapped in stone etc
e.g.: remains of dinosaur bones trapped in stone etc
13. What are fossil fuels?
Answer: Fossil fuels are natural fuels formed from the remains of dead plants and animals that were buried under the earth millions of years ago. With time, heat and pressure turned them into fuels
e.g.: coal, petroleum , natural gas etc
e.g.: coal, petroleum , natural gas etc
Metamorphic Rocks
14. How are metamorphic rocks formed?
Answer: When igneous or sedimentary rocks are under great heat and pressure, they change into metamorphic rocks.
15. Give two examples of metamorphic rocks.
Answer:
- Clay changes into slate
- Limestone changes into marble
Uses of Rocks
16. How are rocks useful to us?
Answer: Rocks are used to make roads, houses, and buildings. Some stones are also used in games.
17. Name some games that use stones.
Answer:
- Seven stones (pitthoo)
- Hopscotch (stapu/kit-kit)
- Five stones (gitti)
The Rock Cycle
18. What is the rock cycle?
Answer: The rock cycle is the process where one type of rock changes into another in a cyclic way under certain conditions.
19. Explain the rock cycle in simple steps.
Answer:
- Molten magma cools → forms igneous rock
- Igneous rocks break down → form sedimentary rocks
- Heat and pressure on these rocks → form metamorphic rocks
- Metamorphic rocks melt again → form molten magma, and the cycle repeats.
Minerals
20. What are minerals?
Answer: Minerals are naturally occurring substances that have specific physical properties and chemical composition.
21. How are minerals useful to us?
Answer: Minerals are used:
- As fuels: coal, petroleum, natural gas
- In industries: iron, aluminium, gold
- In medicine and fertilisers
Word Origins (Etymology)
22. What is the meaning of the word 'Igneous'?
Answer: It comes from the Latin word "Ignis" which means fire.
23. What is the meaning of the word 'Sedimentary'?
Answer: It comes from the Latin word "Sedimentum" which means settle down.
24. What is the meaning of the word 'Metamorphic'?
Answer: It comes from the Greek word "Metamorphose" which means change of form.
Local Resource-Based Question
25. What are some minerals found in Jharkhand?
Answer: Jharkhand has minerals like coal, iron ore, copper, mica, bauxite, and uranium.
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