Class 8 Science Our Home: Earth, a Unique Life-Sustaining Planet
Class 8 Science Our Home: Earth, a Unique Life-Sustaining Planet
1. Introduction
Earth is the only known planet that sustains life. Its unique combination of air, water, land, and climate supports a variety of living organisms. Understanding Earth’s structure and resources helps us protect and conserve it.
2. Earth’s Shape and Size
Shape: Nearly spherical; slightly flattened at poles (oblate spheroid)
Diameter: ~12,742 km
Circumference: ~40,075 km
3. Layers of the Earth
Crust: Outer solid layer; thickness 5–70 km
Mantle: Hot, semi-solid layer below crust
Outer core: Liquid layer; mainly iron and nickel
Inner core: Solid, dense layer; mainly iron and nickel
Lithosphere: Crust + uppermost mantle; supports continents and oceans
4. Atmosphere
Definition: Layer of gases surrounding Earth
Composition:
Nitrogen ~78%
Oxygen ~21%
Other gases (CO₂, argon, water vapor) ~1%
Importance:
Provides oxygen for respiration
Protects from harmful solar radiation
Helps regulate temperature
5. Hydrosphere
Definition: All water on Earth
Distribution:
Oceans: 97%
Ice caps & glaciers: 2%
Rivers, lakes, groundwater: 1%
Importance:
Supports aquatic life
Provides water for drinking, agriculture, industry
Regulates climate
6. Biosphere
Definition: Part of Earth where life exists
Includes: Land, water, and atmosphere supporting life
Importance: Maintains balance of ecosystems
7. Earth’s Unique Features Supporting Life
Liquid water available
Oxygen-rich atmosphere
Suitable temperature for survival
Magnetic field protects from harmful solar radiation
Gravity retains atmosphere and water
8. Human Impact on Earth
Deforestation → loss of habitat and biodiversity
Pollution (air, water, soil) → climate change and health hazards
Overuse of natural resources → depletion of minerals, water
Global warming → melting ice caps, rising sea levels
9. Conservation of Earth
Planting trees and afforestation
Reducing pollution
Sustainable use of resources
Protecting water bodies and wildlife
Promoting renewable energy sources
10. Key Terms
Term
Meaning
Crust
Outer solid layer of Earth
Mantle
Semi-solid layer beneath crust
Core
Central part of Earth, divided into outer (liquid) and inner (solid) core
Lithosphere
Crust + upper mantle
Atmosphere
Layer of gases surrounding Earth
Hydrosphere
All water on Earth
Biosphere
Regions of Earth where life exists
Oblate spheroid
Shape of Earth slightly flattened at poles
Global warming
Increase in Earth’s average temperature
Conservation
Protection and sustainable use of Earth’s resources
11. Examples in Daily Life
Rivers and lakes → water supply for drinking and agriculture
Forests → oxygen production, habitat for animals
Soil → supports crops and plants
Atmosphere → provides air and protects from harmful radiation
12. Possible Questions
Very Short Answer Questions (1–2 marks)
Name the four main layers of Earth.
What is the composition of Earth’s atmosphere?
Define hydrosphere.
Give one example of a human impact on Earth.
Why is Earth called a life-sustaining planet?
Short Answer Questions (3–5 marks)
Explain the importance of lithosphere.
Describe the distribution of water on Earth.
List human activities that affect Earth’s environment.
Explain the unique features of Earth that support life.
Long Answer Questions (6–8 marks)
Describe the structure of Earth with a labeled diagram.
Discuss the importance of atmosphere, hydrosphere, and biosphere.
Explain measures to conserve Earth’s resources and protect the environment.
Discuss the impact of global warming and ways to reduce it.
Multiple Choice Questions (MCQs)
The Earth is: a) Flat b) Perfect sphere c) Oblate spheroid d) Cylinder Answer: c
The outer core of Earth is: a) Solid b) Liquid c) Gas d) None Answer: b
Oceans cover approximately: a) 50% of Earth b) 97% of Earth’s water c) 10% of Earth d) 70% of total area Answer: b
Fill in the Blanks
Lithosphere consists of crust and upper mantle.
Nitrogen makes up 78% of atmosphere.
Biosphere includes regions where life exists.
True/False Questions
Inner core is solid and dense. True
Hydrosphere includes all land on Earth. False
Earth’s magnetic field protects us from solar radiation. True
Match the Following
Column A
Column B
Crust
Outer solid layer
Mantle
Semi-solid layer beneath crust
Outer core
Liquid iron and nickel
Inner core
Solid, dense iron and nickel
Atmosphere
Layer of gases surrounding Earth
Earth’s Shape and Structure
Earth is shaped like a: a) Perfect sphere b) Oblate spheroid c) Cylinder d) Cube Answer: b
Diameter of Earth is approximately: a) 12,742 km b) 40,000 km c) 5,000 km d) 100,000 km Answer: a
Circumference of Earth is about: a) 12,742 km b) 40,075 km c) 29,530 km d) 50,000 km Answer: b
The outermost solid layer of Earth is called: a) Mantle b) Crust c) Core d) Lithosphere Answer: b
The layer below crust is: a) Mantle b) Outer core c) Inner core d) Lithosphere Answer: a
Outer core of Earth is: a) Solid b) Liquid c) Gas d) Semi-solid Answer: b
Inner core of Earth is: a) Solid and dense b) Liquid c) Gas d) Semi-solid Answer: a
Lithosphere includes: a) Crust only b) Upper mantle only c) Crust + upper mantle d) Mantle + core Answer: c
Mantle is mainly: a) Solid b) Semi-solid c) Gas d) Liquid Answer: b
Core is mainly composed of: a) Iron and nickel b) Silicon and oxygen c) Carbon and hydrogen d) Aluminum and magnesium Answer: a
Atmosphere
The atmosphere is: a) Solid layer around Earth b) Layer of gases surrounding Earth c) Liquid layer around Earth d) Core of Earth Answer: b
Nitrogen in atmosphere makes up approximately: a) 21% b) 78% c) 1% d) 50% Answer: b
Oxygen in atmosphere is about: a) 78% b) 21% c) 1% d) 50% Answer: b
Other gases like CO₂, argon, and water vapor make up: a) 1% b) 10% c) 50% d) 25% Answer: a
Atmosphere protects Earth from: a) Harmful solar radiation b) Wind c) Earthquakes d) Volcanic eruptions Answer: a
Oxygen in atmosphere is essential for: a) Photosynthesis b) Respiration c) Combustion d) Both b and c Answer: d
Greenhouse gases in atmosphere help: a) Produce water b) Maintain Earth’s temperature c) Increase UV radiation d) Destroy ozone layer Answer: b
Without atmosphere, Earth would: a) Have same temperature b) Experience extreme temperatures c) Have more water d) Support life easily Answer: b
Water vapor in atmosphere helps: a) Photosynthesis b) Cloud formation c) Magnetic field d) Soil formation Answer: b
Air pollution mainly affects: a) Lithosphere b) Atmosphere c) Core d) Mantle Answer: b
Hydrosphere
Hydrosphere includes: a) All water on Earth b) Only oceans c) Only rivers d) Only glaciers Answer: a
Oceans contain approximately: a) 50% of water b) 97% of water c) 2% of water d) 1% of water Answer: b
Ice caps and glaciers contain approximately: a) 97% b) 2% c) 1% d) 50% Answer: b
Rivers, lakes, and groundwater contain approximately: a) 97% b) 2% c) 1% d) 50% Answer: c
Hydrosphere is important for: a) Aquatic life b) Drinking water c) Agriculture d) All of the above Answer: d
Oceans help regulate: a) Climate b) Sunlight c) Soil formation d) Rock layers Answer: a
Groundwater is stored in: a) Atmosphere b) Aquifers c) Core d) Lithosphere only Answer: b
Melting glaciers contribute to: a) Sea level rise b) Lower temperatures c) Earthquakes d) Soil erosion Answer: a
Water is essential for: a) Photosynthesis b) Drinking c) Industry d) All of the above Answer: d
Oceans are mainly composed of: a) Fresh water b) Salt water c) Pure water d) Polluted water only Answer: b
Biosphere and Life
Biosphere includes regions where: a) Life exists b) Only water exists c) Only soil exists d) Only air exists Answer: a
Plants produce: a) Carbon dioxide b) Oxygen c) Methane d) Nitrogen Answer: b
Animals produce: a) Oxygen b) Carbon dioxide c) Nitrogen d) Sunlight Answer: b
Biodiversity means: a) Variety of ecosystems b) Variety of species c) Variety of water sources d) Only variety of plants Answer: b
High biodiversity helps: a) Maintain ecosystem stability b) Reduce oxygen c) Increase pollution d) Decrease soil fertility Answer: a
Human activities can reduce biodiversity through: a) Deforestation b) Pollution c) Overhunting d) All of the above Answer: d
Forests are important because: a) Provide oxygen b) Maintain ecological balance c) Prevent soil erosion d) All of the above Answer: d
Agriculture depends on: a) Soil b) Water c) Sunlight d) All of the above Answer: d
Urbanization can: a) Increase biodiversity b) Reduce green cover c) Maintain natural habitats d) Increase water availability Answer: b
Overuse of natural resources can lead to: a) Resource depletion b) Climate balance c) Soil fertility improvement d) Increase in biodiversity Answer: a
Conservation and Protection
Planting trees helps: a) Reduce soil erosion b) Maintain oxygen levels c) Protect habitats d) All of the above Answer: d
Using renewable energy sources helps: a) Reduce pollution b) Conserve fossil fuels c) Reduce global warming d) All of the above Answer: d
Protecting water bodies prevents: a) Soil fertility loss b) Water pollution c) Deforestation d) Air pollution Answer: b
Recycling helps: a) Reduce waste b) Conserve resources c) Reduce pollution d) All of the above Answer: d
Reducing vehicle emissions helps: a) Improve air quality b) Decrease oxygen c) Increase pollution d) Reduce water availability Answer: a
True/False
Inner core is solid and dense. True
Hydrosphere includes only oceans. False
Earth’s atmosphere protects us from harmful solar radiation. True