Class 8 Science Curiosity Chapter 13 Solutions (NCERT 2026–27) – Our Home: Earth, a Unique Life Sustaining Planet

These Class 8 Science Curiosity Chapter 13 solutions cover Our Home: Earth, a Unique Life Sustaining Planet from the new NCF-2023 textbook (2026–27), with every “Keep the curiosity alive” question answered step by step.

Class: 8 Subject: Science Book: Curiosity Chapter: 13 Exercise: Keep the curiosity alive (12 Qs) Session: 2026–27
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Class 8 Science Curiosity Chapter 13 Solutions – Overview

Chapter 13 of Curiosity, Our Home: Earth, a Unique Life Sustaining Planet, is the concluding chapter of the Grade 8 book. It explains why Earth is the only known planet that supports life: its position in the habitable (Goldilocks) zone where water stays liquid, its right size to hold an atmosphere by gravity, the protective ozone layer, and the Earth’s magnetic field that helps deflect charged particles from space. It then shows how the atmosphere, hydrosphere, geosphere and biosphere interact to sustain life, how reproduction (asexual and sexual) keeps life going, and how the triple planetary crisis—climate change, biodiversity loss and pollution—threatens this delicate balance. These Class 8 Science Curiosity Chapter 13 solutions answer every textbook question step by step.

Key Concepts & Definitions

Habitable zone (Goldilocks zone): the range of distances from a star where surface liquid water could exist on a planet with suitable atmospheric conditions. Being in this zone does not guarantee water or life. Earth lies in the Sun’s habitable zone.

Greenhouse effect: gases like carbon dioxide trap heat radiated by the warmed Earth, keeping it warm enough for liquid water. A mild greenhouse effect is helpful; too much (as on Venus) makes a planet too hot.

Crust & geosphere: the crust is Earth’s outermost solid layer. The geosphere includes the solid Earth, not just its surface. Life also occurs in water, soil and parts of the atmosphere; it is not restricted to the crust.

The four spheres: atmosphere (air), hydrosphere (water), geosphere (solid Earth), biosphere (all living things and their habitats) — they interact to sustain life.

Ozone layer: the ozone-rich region of the stratosphere. Ozone (O₃) absorbs much of the Sun’s harmful ultraviolet radiation; it is not the same protection as a magnetic field.

Magnetic field: generated mainly by moving, electrically conducting fluid in the outer core. It changes the paths of many charged particles from space; the atmosphere also provides essential radiation shielding.

Reproduction: allows life to continue across generations. Asexual — one parent without gamete fusion; offspring are generally genetically very similar, though mutations can occur. Sexual — fusion of gametes, usually from two parents, combines genetic information. Self-fertilisation can involve one individual.

Triple planetary crisis: climate change, biodiversity loss and pollution — the biggest threats to life on Earth.

“Probe and Ponder” & Activity — Answers

What do you think Earth would look like if there were no life on it at all?

ANSWERThere would be no forests, crops, animals or people, and no structures built by humans. However, a lifeless Earth would not necessarily be a dry copy of Mars or the Moon: rocks, oceans, clouds and weather could still exist, depending on its physical conditions. Without photosynthetic organisms, the atmosphere would not have acquired its present oxygen-rich composition.

Life on Earth has survived for billions of years. What allows it to keep going despite major changes and disasters?

ANSWERReproduction replaces generations, while inherited variation gives natural selection material to act on as conditions change. Mutations occur in both asexual and sexual lineages; sexual reproduction reshuffles genetic information.Liquid water, energy and suitable environments have allowed life to persist in many habitats. This does not mean conditions have always been stable or that every species survives: many lineages became extinct, while others survived and diversified.

Why don’t dogs lay eggs? Or hens give birth to live chicks?

ANSWERDifferent animals have different reproductive strategies. In most mammals like dogs, the zygote develops into an embryo inside the mother’s body, which supplies food and oxygen until birth. In birds like hens, the fertilised egg is laid and the embryo develops outside, using the food stored in the egg until it hatches.

If a spaceship carried soil and water to Mars, could plants start growing there?

ANSWERNot in an unprotected Martian garden. Plants need a controlled growing space with suitable pressure and gas composition, light, temperature, nutrients and liquid water. They use carbon dioxide for photosynthesis and oxygen for respiration. Radiation protection would also be needed. Simply bringing soil and water would not supply all these conditions.

Activity 13.1: List some features of the Earth that we often take for granted, but are interesting and important to us.

ANSWER Some examples beyond those given in the book: (3) Liquid water exists in oceans, rivers, lakes and groundwater, although safe fresh water is unevenly distributed and can be scarce. (4) The temperature stays moderate, so water does not all freeze or boil away. Other valid features: oxygen in the air lets us breathe; the ozone layer blocks harmful UV rays; the magnetic field protects us from harmful space particles; seasons repeat in a steady cycle; soil and minerals supply food and building materials.

Class 8 Science Curiosity Chapter 13 Solutions — 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. This is the intended textbook option: Mars has a very thin atmosphere and no persistent bodies of liquid water on its surface today. It does have water ice and evidence of ancient rivers and lakes.These conditions make its surface unsuitable for unprotected Earth-like life. They do not prove that no microbial life could ever have existed or could exist in a protected habitat. See NASA’s Mars facts.

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. Geodiversity is the variety of landforms, rocks and soils, together with the processes that shape them. Options (i) and (iv) describe living variety (biodiversity) and (iii) describes weather.

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) is the intended option. At the same density, a smaller planet has less mass, weaker surface gravity and a lower escape speed, so it would tend to lose atmospheric gases more easily.This is a tendency, not instant or complete loss: atmospheric retention also depends on temperature, gas composition and processes that add or remove gases.

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. In sexual reproduction the gametes from two parents combine, so the offspring inherit a new mix of genetic instructions — sharing some traits with each parent but also showing differences (variation).

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?

ANSWERSeeds of flowering plants could arrive by wind, rainwater or birds and other animals, then lodge in cracks containing dust or debris.Most seeds need water, oxygen and a suitable temperature to germinate. Sunlight and soil are not universal requirements for the initial germination step; seedlings later need light for photosynthesis and a supply of mineral nutrients.If the green growth is moss, fern or algae rather than a seed plant, it may have arrived as spores or cells instead. Observe the plant before assuming all green growth came from seeds.

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?

ANSWERLocal climate: loss of shade and transpiration can raise local temperatures; roads and buildings may store additional heat. Clearing trees also reduces carbon storage. Effects on rainfall depend on the scale of clearing and regional conditions.Biodiversity: habitat loss and fragmentation remove food, shelter and movement routes, potentially reducing plant and animal populations and disrupting food webs.Water: paving and compacted soil can increase runoff and reduce infiltration and groundwater recharge. Eroded soil and road pollutants can enter streams. Recharge may decrease; it does not necessarily stop everywhere.

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?

ANSWERPast natural climate change does not explain away today’s warming. Evidence identifies human greenhouse-gas emissions as the main cause of recent global warming. Burning fossil fuels adds carbon dioxide; methane also comes from leaks during fuel production, livestock and waste.Higher greenhouse-gas concentrations reduce the rate at which Earth initially loses heat to space, causing warming until the energy balance adjusts. Current warming raises risks for ecosystems and people, including heat extremes, sea-level rise and changing rainfall.Reference: IPCC Sixth Assessment Synthesis Report.

8. Imagine Earth’s magnetic field suddenly disappeared. What kinds of problems could arise for life on Earth? Explain.

ANSWEREarth’s magnetic environment deflects many charged particles. Without it, near-Earth space would be more exposed to particles from the Sun, with increased risks for spacecraft and astronauts and possible changes in the upper atmosphere.The atmosphere would still provide shielding at the surface. It would not instantly vanish, nor would all life immediately die. The amount and timescale of atmospheric change would depend on several processes.Distinguish the protections: ozone absorbs ultraviolet light; the magnetic field acts on charged particles. It does not directly block UV. See NASA’s magnetosphere explanation.
Comparison of ozone absorbing ultraviolet light, magnetic fields deflecting charged particles, and the atmosphere helping maintain pressure and temperature.
Different protections work in different ways. This teaching sketch is schematic and not to scale. Tap to view at full size.

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?

ANSWERA settlement would need (1) breathable air at suitable pressure, (2) reliable liquid water and recycling, and (3) a heated, radiation-shielded habitat. It would also need food, energy and waste management.One reasonable choice for the hardest task is maintaining a reliable, closed life-support system for years: oxygen, carbon dioxide removal, water recycling and equipment repair must all work together. Another defensible choice is radiation shielding, because effective protection requires substantial material.The question asks for a settlement, so a sealed habitat is enough for the design answer; recreating an atmosphere or magnetic field for the whole planet is not required. An ozone-like screen alone would not stop high-energy charged particles.

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.

ANSWERPossible causes: global warming can contribute to higher temperatures and changing rainfall; local land clearing and natural year-to-year variability may also matter. A few years of village observations alone cannot establish the precise cause.Two adaptations: (1) collect and safely store rainwater and improve irrigation efficiency; (2) select locally suitable drought-tolerant crops and adjust sowing dates using weather advice. Native shade trees can help reduce heat exposure.Using clean energy reduces emissions: this is mitigation. Adjusting farming and water use to cope with impacts is adaptation.

11. If there were no atmosphere on the Earth, would it affect life, temperature, and water on the planet? Explain.

ANSWER Yes, it would seriously affect all three. Life: there would be no oxygen to breathe and no ozone layer, so harmful UV rays and space particles would reach the surface — most life could not survive. Temperature: with no atmosphere there would be no greenhouse effect, so the Earth would lose its heat to space and become extremely cold (and scorching where the Sun shines directly), with huge swings between day and night. Water: without atmospheric pressure and warmth, liquid water could not remain stable on the surface — it would freeze or evaporate away, so the oceans and rivers as we know them could not exist.

12. Discuss five examples of vegetative propagation.

ANSWERVegetative propagation produces new plants from vegetative parts rather than seeds. Five examples are:
  1. Potato: buds in the “eyes” of a stem tuber grow into shoots. A suitable piece must contain a bud.
  2. Ginger: buds on its horizontal underground stem, the rhizome, form new shoots and roots.
  3. Money plant: a stem cutting containing a node can develop roots and a new shoot in water or a suitable moist medium.
  4. Sugarcane: stem pieces containing viable buds at nodes can establish new plants.
  5. Onion: buds in a bulb can grow; daughter bulbs can separate to form new plants. A bulb has a short stem surrounded by fleshy storage leaves.
These are generally genetically similar to the parent, apart from possible mutations. A potato tuber and a ginger rhizome are modified stems, not roots.
Five vegetative propagation examples: potato stem tuber eye, ginger rhizome bud, money plant node, sugarcane node bud and onion bulb bud.
Locate the bud or node that can produce a new shoot. Drawings show the key structures, not scale or a guaranteed growth timetable. Tap to view at full size.

Common Misconceptions to Avoid

Watch out for these

  • Thinking the hottest planet is the closest one — Venus is hotter than Mercury because its thick carbon-dioxide atmosphere traps heat (greenhouse effect).
  • Believing the greenhouse effect is always bad — a mild greenhouse effect keeps Earth warm enough for liquid water; only excess greenhouse gases cause harmful global warming.
  • Confusing the planet’s greenhouse effect with a plant greenhouse — the planet’s effect works by gases absorbing radiation, not just by trapping warm air behind glass.
  • Assuming every planet in the habitable zone must support life — the zone indicates possible surface liquid water under suitable conditions; atmosphere and other planetary properties still matter.
  • Mixing up the four spheres — geosphere (solid), hydrosphere (water), atmosphere (air), biosphere (life).
  • Thinking asexual reproduction can never produce variation — mutations can introduce differences; sexual reproduction also reshuffles genetic information.

Extra Practice Questions

These questions and MCQs are ClearStudy practice, separate from the NCERT exercise.

Very Short Answer Type Questions

Q1. What is the other name for the habitable zone?

ANSWERThe Goldilocks zone.

Q2. Name the layer of the atmosphere that blocks harmful UV rays.

ANSWERThe ozone layer.

Q3. What are the three challenges together called the “triple planetary crisis”?

ANSWERClimate change, biodiversity loss and pollution.

Short Answer Type Questions

Q1. Why is liquid water important for Earth being a unique planet?

ANSWERAs far as we know, liquid water is essential for life to develop and survive. Earth lies at just the right distance from the Sun (the habitable zone), so water stays mostly liquid instead of freezing or evaporating — this is a key reason Earth can support life and looks blue from space.

Q2. Name the four spheres of the Earth system and what each consists of.

ANSWERThe atmosphere (air), hydrosphere (water), geosphere (the solid part — rocks, soil and minerals) and biosphere (all living things and their habitats). They interact and together sustain life on Earth.

Long Answer Type Question

Q1. Explain the main factors that make the Earth suitable for life to exist.

ANSWEREnergy and water: Earth receives sunlight and has extensive liquid water. Its atmosphere and distance from the Sun help maintain suitable conditions.Gravity and atmosphere: gravity helps retain air. Atmospheric pressure and the natural greenhouse effect help sustain liquid surface water. Oxygen supports aerobic respiration, although not all life needs oxygen.Protection: ozone absorbs harmful UV; the magnetic field and atmosphere help protect against energetic charged particles. Nutrients and interactions among the four Earth systems also support life.Earth’s slightly elliptical orbit produces modest changes in solar distance. The seasons mainly result from axial tilt; temperatures are not constant throughout the year.

MCQs & Assertion–Reason

1. The range of distances from a star where water can stay liquid is called the:

(a) ozone zone    (b) habitable (Goldilocks) zone    (c) magnetic zone    (d) greenhouse zone

2. Earth is called the “Blue Planet” mainly because:

(a) the sky looks blue    (b) it is cold    (c) most of its surface is covered with water    (d) it has a blue core

3. The hottest planet in the solar system is Venus because:

(a) it is closest to the Sun    (b) its thick atmosphere traps heat    (c) it has no atmosphere    (d) it has a strong magnetic field

4. The solid part of the Earth — rocks, soil and minerals — is called the:

(a) hydrosphere    (b) atmosphere    (c) geosphere    (d) biosphere

5. The Earth’s magnetic field protects us by deflecting:

(a) sunlight    (b) rainwater    (c) cosmic rays and the solar wind    (d) clouds

6. The ozone layer is important because it:

(a) provides oxygen to breathe    (b) blocks harmful ultraviolet rays    (c) makes rain    (d) creates gravity

7. Growing a new plant from a stem cutting of money plant is an example of:

(a) sexual reproduction    (b) pollination    (c) vegetative propagation    (d) fertilisation

8. In flowering plants, the male gametes are present in the:

(a) ovule    (b) pollen grains (anther)    (c) root    (d) fruit

9. The triple planetary crisis includes climate change, pollution and:

(a) earthquakes    (b) biodiversity loss    (c) volcanoes    (d) tides

10. On Mars, compared with Earth, the atmosphere is:

(a) much thicker    (b) about 100 times thinner    (c) exactly the same    (d) made mostly of oxygen

Answer key: 1-(b), 2-(c), 3-(b), 4-(c), 5-(c), 6-(b), 7-(c), 8-(b), 9-(b), 10-(b).

For each Assertion–Reason question, choose: (A) Both true and the Reason correctly explains the Assertion; (B) Both true but the Reason is not the correct explanation; (C) Assertion true, Reason false; (D) Assertion false, Reason true.

A-R 1. Assertion: Earth lies in the habitable zone of the Sun.

Reason: At Earth’s distance from the Sun, the temperature allows water to remain in liquid form.

A-R 2. Assertion: Venus is hotter than Mercury even though Mercury is closer to the Sun.

Reason: Venus has a thick carbon-dioxide atmosphere that traps heat through the greenhouse effect.

A-R 3. Assertion: A smaller planet of the same density tends to retain atmospheric gases less easily, other factors being comparable.

Reason: A smaller planet has stronger gravity that pulls the atmosphere inward.

A-R 4. Assertion: Asexual reproduction produces offspring with great variation from the parent.

Reason: Asexual reproduction usually produces genetically similar offspring from one parent, although mutations may occur.

A-R 5. Assertion: The Earth’s magnetic field helps protect life on the planet.

Reason: It deflects harmful cosmic rays and the solar wind away from the Earth.

Answer key: 1-(A), 2-(A), 3-(C), 4-(D), 5-(A).

Quick Revision Summary

  • Earth is a unique planet because it supports life; it lies in the habitable (Goldilocks) zone where water stays liquid.
  • Gravity helps retain the atmosphere. Earth’s axial tilt causes seasons, so temperatures vary during the year.
  • The ozone layer blocks harmful UV rays; the magnetic field shields Earth from cosmic rays and the solar wind.
  • The atmosphere, hydrosphere, geosphere and biosphere interact and together sustain life.
  • Reproduction continues lineages: asexual offspring are usually genetically similar; sexual reproduction combines gametes and reshuffles genetic information.
  • Climate change, biodiversity loss and pollution form the triple planetary crisis; balance must be protected.

Real-life Applications

Understanding Earth’s habitable conditions guides real choices: rainwater harvesting and tree planting help villages cope with rising temperatures and uncertain rains; using clean energy like solar and wind cuts greenhouse gases; reusing, repairing and recycling reduce pollution and waste. Knowing about the ozone layer led the world to the Montreal Protocol to phase out CFCs, while the Paris Agreement targets limiting global warming. Space missions like India’s Mangalyaan study whether other planets could ever support life.

How to write a clear answer

Learn the four factors that make Earth habitable (position, size, ozone layer, magnetic field) and the four spheres with one line each. Remember why Venus is the hottest planet (greenhouse effect, not distance). For reproduction questions, clearly contrast asexual (one parent, usually genetically similar) with sexual (gamete fusion, usually two parents, reshuffled genes), and keep five vegetative-propagation examples ready (potato, ginger, money plant, sugarcane, onion).

Frequently Asked Questions

What is Class 8 Science Curiosity Chapter 13 about?

It explains why Earth is a unique, life-sustaining planet — its position in the habitable (Goldilocks) zone, its right size and atmosphere, the ozone layer and magnetic field, how its four spheres sustain life, how reproduction continues life, and the threats of the triple planetary crisis.

What is the habitable zone or Goldilocks zone?

It is the range of distances from a star where surface liquid water could exist on a planet with a suitable atmosphere. Being in the zone does not guarantee water or life. Earth lies in this zone around the Sun.

How many questions are in the “Keep the curiosity alive” exercise of Chapter 13?

There are 12 questions, all solved on this page along with the “Probe and ponder” prompts and the activity.

Are these Class 8 Science Curiosity Chapter 13 solutions free?

Yes. All solutions are free and follow the official NCERT Curiosity textbook for 2026–27.

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