Class 8 Science Chapter 13 – Our Home: Earth, a Unique Life Sustaining Planet from NCERT Curiosity with easy Notes and complete Book Solutions. Get simple explanations, important concepts, questions and answers, and revision material for effective learning, practice and exam preparation.
Our Home: Earth, a Unique Life Sustaining Planet
Class 8 Science – Curiosity
Chapter 13
Short Easy Notes, Concepts and Book Questions
Probe and Ponder
What do you think Earth would look like if there were no life on it at all?
Answer: Earth would look mostly lifeless, with no plants, animals, humans or microorganisms. Its landscapes, water and rocks would still be present.
Life on Earth has survived for billions of years. What allows it to keep going despite major changes and disasters?
Answer: Suitable conditions, reproduction, adaptation, biodiversity and the balance between living and non-living components help life continue.
Why don’t dogs lay eggs? Or hens give birth to live chicks?
Answer: Different animals have different reproductive systems. Dogs are mammals and usually give birth to young ones, while hens are birds and lay eggs.
If a spaceship carried soil and water to Mars, could plants start growing there?
Answer: Not easily. Plants need suitable temperature, atmosphere, nutrients, water and other conditions. Mars does not naturally provide all these conditions.
Share your questions
Think: Write any science question you have about Earth, life or space.
13.1 Why Is Earth a Unique Planet?
Earth supports life.
Earth has liquid water, a suitable atmosphere, moderate temperature, soil, sunlight and protection from harmful space particles.
Earth has liquid water, a suitable atmosphere, moderate temperature, soil, sunlight and protection from harmful space particles.
Earth’s crust:
The crust is the thin outer layer of Earth where life exists.
The crust is the thin outer layer of Earth where life exists.
Easy idea: If Earth were the size of an apple, its crust would be like the thin skin of the apple.
Activity 13.1 – Let us find out
List some features of the Earth that we often take for granted, but are interesting and important to us. Write them in Table 13.1. We have filled in a few for you.
| S.No. | Interesting features of the Earth |
|---|---|
| 1. | The air we breathe doesn’t fly off and disappear into space. |
| 2. | We can stand on the ground held by gravity, but our heart can pump blood up to our head. |
| 3. | Earth has liquid water. |
| 4. | Earth has an atmosphere suitable for life. |
Easy conclusion: Earth provides air, water, soil, minerals and suitable conditions needed for life.
13.2 What Do the Planets of Our Solar System Look Like?
Our solar system has eight planets that orbit the Sun.
1. MercuryRocky planet
2. VenusRocky planet
3. EarthRocky planet
4. MarsRocky planet
5. JupiterLarge gas-rich planet
6. SaturnLarge gas-rich planet
7. UranusLarge gas-rich planet
8. NeptuneLarge gas-rich planet
Activity 13.2 – Let us find out
Collect information about the temperature and size of the planets in the solar system, and check if they have an atmosphere.
Tip: Use your textbook, school library or trusted science sources to complete the table.
You may collect this information from books in your school library, trusted websites, or discuss with your teachers.
Answer: This is an information-gathering activity. Record the information in Table 13.2.
Fill out the missing information in Table 13.2.
| S.No. | Planet | Average temperature | Radius, compared to the Earth | Has an atmosphere? |
|---|---|---|---|---|
| 1. | Mercury | 170 °C | Small | No |
| 2. | Venus | 450 °C | 0.95 | Yes |
| 3. | Earth | 15 °C | 1 | Yes |
| 4. | Mars | Very cold | Smaller than Earth | Yes, very thin |
| 5. | Jupiter | Very cold | About 11 | Yes |
| 6. | Saturn | Very cold | About 9 | Yes |
| 7. | Uranus | Very cold | About 4 | Yes |
| 8. | Neptune | –200 °C | About 4 | Yes |
Is this what you found in Table 13.2?
Answer: Generally, planets farther from the Sun are colder. Venus is an important exception because its thick atmosphere traps a lot of heat.
Greenhouse effect: Gases such as carbon dioxide absorb radiation and help trap heat in the atmosphere.
Why is Venus the hottest planet?
Answer: Venus has a very thick atmosphere rich in carbon dioxide. It traps a large amount of heat.
A Step Further
Is the temperature or distance from the Sun, the only factor that makes the Earth habitable?
Answer: No. Earth’s size, atmosphere, magnetic field, liquid water and other conditions also make it suitable for life.
What would happen if the size of the Earth were too small or too big?
Answer: If Earth were too small, its gravity might not hold the atmosphere. If it were too large, its gravity could be too strong for life as we know it.
13.3 What Makes the Earth Suitable for Life to Exist?
13.3.1 Position of the Earth
Earth is at a suitable distance from the Sun. This allows water to remain mostly in liquid form.
Habitable Zone / Goldilocks Zone: The range around a star where conditions may allow liquid water to exist.
Too Hot
→
Habitable Zone – Just Right
→
Too Cold
Did Mars ever support life?
Did Mars ever support life?
Answer: No proof of past life has been found yet. Scientists think Mars may have had liquid water in the past, so it continues to be studied.
13.3.2 Size of the Earth
Earth’s size gives it enough gravity to hold its atmosphere.
The atmosphere contains gases needed for life and also helps maintain temperature.
The ozone layer absorbs much of the harmful ultraviolet radiation from the Sun.
Our Scientific Heritage – Mangalyaan
India’s Mangalyaan, launched by ISRO in 2013, studied Mars and its atmosphere, surface and possible signs of past water.
13.3.3 Magnetic Field of the Earth
Earth behaves like a giant magnet. Its magnetic field acts as a protective shield against many harmful charged particles from the Sun and space.
Does the magnetic field of the Earth have any role in sustaining life on Earth?
Answer: Yes. It helps protect Earth from many harmful high-energy particles from space and the solar wind.
Earth’s life-supporting conditions: Suitable distance from the Sun + liquid water + suitable size + atmosphere + ozone layer + magnetic field.
13.4 What Allows Life to Be Sustained on Earth?
Life survives because living and non-living components of Earth work together.
Atmosphere
Air and gases around Earth.
Hydrosphere
All the water on Earth.
Geosphere
Solid parts such as rocks, soil and minerals.
Biosphere
All living organisms and places where life exists.
Sunlight
Provides energy for life and photosynthesis.
Soil
Provides support and nutrients for plants.
13.4.1 Air, Water, and Sunlight
Plants use carbon dioxide, water and sunlight to make food through photosynthesis. Oxygen released during photosynthesis is used by many organisms for respiration.
The greenhouse effect keeps Earth’s temperature suitable for liquid water.
Water is essential for drinking, photosynthesis, transport of nutrients, digestion and temperature regulation.
Water vapour forms clouds and contributes to rainfall, which refills rivers, lakes and groundwater.
13.4.2 Soil, Rocks, and Minerals
Rocks, soil and minerals form the geosphere. Soil provides plants with nutrients such as nitrogen and potassium.
Geodiversity: The variety of landforms, rocks, soils and geological processes on Earth.
13.4.3 Plants, Animals, and Microorganisms
Plants, animals and microorganisms together with their surroundings form the biosphere.
Plants make food
→
Animals depend on food
→
Decomposers recycle nutrients
13.4.4 The Importance of Balance
A change in one part of Earth can affect many other parts. For example, cutting forests can affect rainfall, soil, air quality, water and animals.
13.5 What Keeps Life from Disappearing?
Reproduction ensures that living organisms continue from one generation to the next.
Genes contain instructions that help organisms develop their characteristics.
Asexual Reproduction
One parent is involved. New individuals are usually genetically very similar to the parent.
Sexual Reproduction
Genetic material from two parents combines.
Variation
Differences among offspring can help populations adapt over generations.
13.5.1 Asexual Reproduction
Vegetative propagation: A new plant develops from a part such as a stem, leaf or root.
Can you observe and list some plants around you that grow this way?
Answer: Examples include potato, ginger, money plant, sugarcane and some other plants that can grow from vegetative parts.
Activity 13.3 – Let us find out
Take some parts of plants like stem cutting of a money plant, the ‘eyes’ of a sprouted potato, or a piece of ginger (Fig. 13.11b).
Activity: Plant them separately in moist soil and observe their growth.
Plant each of them separately in moist soil (not too deep). For money plant, you can just put a cutting in a glass container which makes it easy to observe.
Observation: Look for roots, stems and leaves developing from the planted part.
Make sure they get all the conditions they need to grow—like water, air, and sunlight.
Reason: These conditions support healthy plant growth.
Watch them every day and note how many days it takes for roots stem and leaves to appear. Also observe when the first new leaf appears.
Activity answer: Record your own observations because the time may differ for each plant.
Asexual Reproduction in Other Organisms
Bacteria and amoebae can divide into two. Hydra can form buds. Planaria can regenerate from body pieces.
13.5.2 Sexual Reproduction
Sexual reproduction usually involves two parents. Special reproductive cells called gametes carry genetic material.
When male and female gametes join, they form a zygote.
Offspring receive genetic information from both parents, so they may have similarities as well as differences.
Sexual Reproduction in Plants
Pollen
→
Pollination
→
Fertilisation
→
Zygote
→
Seed
Pollination: Transfer of pollen to the female part of a flower.
Fertilisation: Fusion of male and female gametes.
Sexual Reproduction in Animals
Male gametes are called sperm and female gametes are called eggs.
In fish and frogs, fertilisation may occur in water. In birds and mammals, fertilisation generally occurs inside the female body.
What are the advantages and disadvantages of giving birth to young ones vs. laying eggs? Do you think animals like dogs, cows, or humans could lay eggs like birds? Why or why not?
Answer: Giving birth allows the developing baby to receive protection and nourishment inside the mother’s body. Laying eggs allows the mother to leave the eggs outside, but the eggs may face environmental dangers. Dogs, cows and humans cannot lay eggs like birds because their reproductive systems and development processes are different.
13.6 What Are the Threats to Life on Earth?
The three major environmental challenges are climate change, biodiversity loss and pollution. Together they are called the triple planetary crisis.
Climate Change
Long-term changes in temperature, rainfall and weather patterns.
Biodiversity Loss
Reduction or disappearance of different forms of life.
Pollution
Harmful substances entering air, water or soil.
Burning fossil fuels releases greenhouse gases such as carbon dioxide and methane. These gases increase heat trapping in the atmosphere.
Destruction of habitats can cause plants and animals to disappear and disturb food chains and ecosystems.
Air pollution can harm people, plants and animals and can contribute to smog and acid rain.
Water and soil pollution can harm aquatic life, reduce soil quality and allow harmful substances to enter food chains.
What can we do?
Save water and energy, reduce waste, reuse and repair items, recycle materials, protect biodiversity, use cleaner energy and support sustainable practices.
Save water and energy, reduce waste, reuse and repair items, recycle materials, protect biodiversity, use cleaner energy and support sustainable practices.
Important Environmental Agreements
| Agreement | Main purpose |
|---|---|
| Montreal Protocol | Helped reduce ozone-depleting substances such as CFCs. |
| Earth Summit | Encouraged international environmental cooperation. |
| Kyoto Protocol | Focused on reducing greenhouse gas emissions. |
| Paris Agreement | International effort to address climate change and limit global warming. |
Snapshots – Quick Revision
- Earth is a unique planet because it supports life.
- Earth lies in the habitable or Goldilocks zone.
- Liquid water is essential for life as we know it.
- Earth’s size helps it hold its atmosphere.
- The ozone layer protects life from harmful ultraviolet rays.
- Earth’s magnetic field provides protection from many harmful space particles.
- Atmosphere, hydrosphere, geosphere and biosphere interact to sustain life.
- Reproduction ensures continuity of life.
- Asexual reproduction involves one parent.
- Sexual reproduction involves genetic material from two parents.
- Pollination transfers pollen to the female part of a flower.
- Fertilisation forms a zygote.
- Climate change, biodiversity loss and pollution form the triple planetary crisis.
Keep the Curiosity Alive
1. What is one major reason Mars cannot currently support life like Earth?
(i) It has too many volcanoes.
(ii) It is too close to the Sun.
(iii) It lacks a thick atmosphere and liquid water.
(iv) Its magnetic field is too strong.
Answer: (iii) It lacks a thick atmosphere and liquid water.
2. Which of these is an example of geodiversity?
(i) Variety of bird chirping in a forest.
(ii) Different landforms like mountains, valleys, and deserts.
(iii) Changing weather during monsoons.
(iv) Number of different types of fish in a pond.
Answer: (ii) Different landforms like mountains, valleys, and deserts.
3. If the Earth were smaller with the same density, what might happen to its atmosphere?
(i) It would become thicker and hotter.
(ii) It would escape into space due to weaker gravity.
(iii) It would become frozen.
(iv) It would cause stronger winds.
Answer: (ii) It would escape into space due to weaker gravity.
4. In sexual reproduction, why are offspring different from their parents?
(i) They grow in different climates.
(ii) They eat different food.
(iii) They acquire new instructions after birth.
(iv) They get mixed instructions (genes) from both parents.
Answer: (iv) They get mixed instructions (genes) from both parents.
5. You notice tiny green plants growing in cracks on your school wall after the monsoon. Where do you think the seeds came from? What conditions helped these plants grow there?
Answer: Seeds may have been carried by wind, birds or water. Moisture, air, sunlight and a suitable place helped them grow.
6. A city has recently cut down a large patch of forest to build new roads and buildings. Discuss the possible effects this could have on the local climate and biodiversity? How might this affect water availability or quality in the area?
Answer: Forest loss can reduce biodiversity, disturb habitats, increase temperature and affect rainfall. It can also increase soil erosion and reduce groundwater recharge, affecting water availability and quality.
7. A friend says, “The Earth has always had climate changes in the past, so today’s global warming is nothing new.” How would you respond using what you’ve learnt in this and other chapters of your science book?
Answer: Earth has experienced natural climate changes, but today’s warming is strongly influenced by human activities such as burning fossil fuels, which increase greenhouse gases.
Prepare some questions based on your learnings so far …
Why? When?
How long?
Where? Why not?
8. Imagine Earth’s magnetic field suddenly disappeared. What kinds of problems could arise for life on Earth? Explain.
Answer: More harmful charged particles from the Sun and space could reach Earth. They could damage the atmosphere and increase harmful radiation reaching living organisms.
9. You are tasked with designing a new settlement for humans on Mars. Name three things you would need to recreate from Earth to support human life there. Which of these do you think is the hardest to replicate, and why?
Answer: We would need breathable air, liquid water and suitable temperature and protection. Creating a complete Earth-like atmosphere and long-term life-support system would be very difficult.
10. In a village, the temperature has been increasing and rainfall has become unpredictable over the past few years. What could be causing this change? Suggest two ways the village could adapt to these new conditions.
Answer: Climate change can cause such changes. The village could conserve water, use rainwater harvesting, grow suitable crops and protect trees.
11. If there were no atmosphere on the Earth, would it affect life, temperature, and water on the planet? Explain.
Answer: Yes. Without the atmosphere, Earth would lose much of its heat, harmful radiation would reach the surface more easily, and liquid water would not remain in the same way. Life as we know it could not survive.
12. Discuss five examples of vegetative propagation.
Answer: Five examples are:
- Potato – eyes
- Ginger – stem/rhizome
- Money plant – stem cutting
- Sugarcane – stem pieces
- Rose – stem cutting
Discover, Design, and Debate
Design an ‘Earth Survival Kit’. Imagine you’re building a tiny model of Earth for another planet. What must it have to support life, and why?
Sample answer: It should have water, air, suitable temperature, soil, nutrients, sunlight and protection from harmful radiation. These are needed to support living organisms.
India is planning for a challenging lunar mission, Chandrayaan-4, which will bring back samples of soil from the Moon. If the Moon had water, could plants grow in that soil? Think of some experiment that could help you explore whether plant growth is possible on the Moon.
Sample answer: Water alone may not be enough. We could grow the same type of seeds in lunar soil and normal soil under similar conditions and compare germination and growth.
Flowers are often brightly coloured and have a pleasant smell. How do you think these features help the plant reproduce?
Answer: Bright colours and pleasant smells can attract insects and other animals that help in pollination.
Why do animals like fish and frogs lay hundreds or even thousands of eggs at a time, while other animals lay only a few? What might be the advantages and disadvantages of laying so many eggs?
Answer: Many eggs may increase the chance that some young ones survive. However, many eggs and young ones may be eaten or may not survive because of environmental conditions.
Birds like sparrows build nests and care for their eggs and chicks, while reptiles like snakes usually lay their eggs and leave them without protection. How might this difference in parental care affect the chances of survival for the young ones in each case?
Answer: Parental care can protect young ones from predators and help provide food, increasing their chances of survival. Young reptiles may face more dangers when parents do not provide such care.
Reflect on the questions framed by your friends and try to answer …
Chapter 13 – One-Page Revision
Why Earth?
Liquid water, suitable temperature, atmosphere, ozone and magnetic field.
Habitable Zone
Region where liquid water can exist under suitable conditions.
Atmosphere
Provides gases and helps regulate temperature.
Hydrosphere
All water on Earth.
Geosphere
Rocks, soil and minerals.
Biosphere
All living things and their surroundings.
Reproduction
Ensures continuity of life.
Asexual
One parent.
Sexual
Genetic material from two parents.
Pollination
Transfer of pollen.
Fertilisation
Fusion of male and female gametes.
Triple Planetary Crisis
Climate change, biodiversity loss and pollution.
Important Terms to Remember
| Term | Easy Meaning |
|---|---|
| Crust | Thin outer layer of Earth where life exists. |
| Habitable Zone | Region around a star where liquid water may exist. |
| Greenhouse Effect | Atmospheric gases trap some heat and keep Earth warm. |
| Ozone Layer | Layer that absorbs much harmful UV radiation. |
| Magnetic Field | Protective field around Earth. |
| Geodiversity | Variety of Earth’s landforms, rocks and soils. |
| Biosphere | Part of Earth where life exists. |
| Gene | Unit of genetic information. |
| Gamete | Special reproductive cell. |
| Zygote | Cell formed after male and female gametes fuse. |
| Vegetative Propagation | New plant grows from a vegetative part of a parent plant. |
| Triple Planetary Crisis | Climate change, biodiversity loss and pollution. |
Prepare with this NCERT Curiosity worksheet for Chapter 13. The worksheet includes important questions and revision exercises to help students understand key concepts, practise what they have learned, and prepare effectively for class tests and exams.
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