What is Earth Exercises in Class 8 Science NCERT?

The Class 8 Science NCERT Chapter 13 — Our Home Earth: A Unique Life-Sustaining Planet exercise section tests students on all the key concepts covered in the chapter, including NCERT exercises, earth questions, atmosphere questions, conservation questions, competency-based questions. It includes mu…

What does the NCERT Class 8 Science Our Home Earth: A Unique Life-Sustaining Planet exercise section cover?

The Class 8 Science NCERT Chapter 13 u2014 Our Home Earth: A Unique Life-Sustaining Planet exercise section tests students on all the key concepts covered in the chapter, including NCERT exercises, earth questions, atmosphere questions, conservation questions, competency-based questions. It includes multiple-choice questions (MCQs), assertion-reason questions, short-answer questions, long-answer questions, and competency-based questions that align with the NCERT Curiosity textbook. Working through these exercises helps Class 8 students reinforce their conceptual understanding, prepare for classroom assessments, and build exam readiness for CBSE school tests. Each question links back to a specific section of the chapter so students can revise the theory alongside the practice.

How should Class 8 students approach the Our Home Earth: A Unique Life-Sustaining Planet exercises?

Class 8 students should approach the Our Home Earth: A Unique Life-Sustaining Planet exercises by first revising the main theory and definitions from each part of the chapter, especially around NCERT exercises and earth questions. Start with the MCQs and assertion-reason questions to quickly test recall, then attempt the short-answer questions that need a one or two-line explanation, and finally tackle the long-answer and competency-based questions that require applying concepts to new situations. Write neat diagrams wherever the question involves a process, cycle, or setup, and always use NCERT-style vocabulary in your answers to match CBSE marking schemes.

Are these Our Home Earth: A Unique Life-Sustaining Planet questions competency-based as per NEP 2020?

Yes, the Our Home Earth: A Unique Life-Sustaining Planet exercise set follows the NEP 2020 competency-based education (CBE) framework used by CBSE and NCERT for Class 8 Science. Instead of only asking students to recall definitions, many questions are scenario-based and require applying the concept to real-life situations, analysing data, or evaluating claims. This matches Bloom's Taxonomy levels L3 (Apply), L4 (Analyse), and L5 (Evaluate), going beyond rote learning. Students practising these questions build the higher-order thinking skills that modern CBSE school exams increasingly assess, and also prepare well for competitive foundation tests in later years.

Which NCERT Curiosity sections are tested in Chapter 13 exercises?

The Chapter 13 u2014 Our Home Earth: A Unique Life-Sustaining Planet exercise set systematically tests every major section of the NCERT Curiosity Class 8 Science textbook for this chapter. Topics covered include NCERT exercises, earth questions, atmosphere questions, conservation questions, competency-based questions. Every in-text question, activity-linked question, and end-of-chapter question from the Curiosity book is represented, so students can be confident that completing this exercise set gives them full coverage of the NCERT syllabus. Teachers also frequently pick questions from these sections for school unit tests and half-yearly exams, making thorough practice essential for strong performance.

How do assertion-reason questions work in this Class 8 Science chapter?

Assertion-reason questions in the Class 8 Science Our Home Earth: A Unique Life-Sustaining Planet exercise set present two statements u2014 an Assertion (A) and a Reason (R) u2014 and ask students to judge whether each is true and whether R correctly explains A. Students pick from four standard options: both true with R explaining A, both true but R not explaining A, A true and R false, or A false. This format tests whether Class 8 learners genuinely understand the cause-and-effect relationships behind NCERT exercises, not just surface facts. Mastering this format is valuable because CBSE Class 10 board exams use the same pattern.

What is the best revision strategy before attempting these exercises?

The best revision strategy before attempting Our Home Earth: A Unique Life-Sustaining Planet exercises is to read through all theory parts of NCERT Curiosity Chapter 13 once, write down the key terms such as NCERT exercises, earth questions, atmosphere questions, conservation questions, competency-based questions in your own words, and then re-do all activities mentally to understand the underlying concept. Next, make a one-page mind map linking the main ideas. Only then attempt the exercise questions u2014 first without looking back, then self-correcting. This active-recall approach builds much stronger long-term memory than repeatedly re-reading the textbook, and is widely recommended by CBSE teachers for Class 8 Science preparation.

What does the NCERT Class 8 Science Our Home Earth: A Unique Life-Sustaining Planet exercise section cover?

The Class 8 Science NCERT Chapter 13 — Our Home Earth: A Unique Life-Sustaining Planet exercise section tests students on all the key concepts covered in the chapter, including NCERT exercises, earth questions, atmosphere questions, conservation questions, competency-based questions. It includes multiple-choice questions (MCQs), assertion-reason questions, short-answer questions, long-answer questions, and competency-based questions that align with the NCERT Curiosity textbook. Working through these exercises helps Class 8 students reinforce their conceptual understanding, prepare for classroom assessments, and build exam readiness for CBSE school tests. Each question links back to a specific section of the chapter so students can revise the theory alongside the practice.

How should Class 8 students approach the Our Home Earth: A Unique Life-Sustaining Planet exercises?

Class 8 students should approach the Our Home Earth: A Unique Life-Sustaining Planet exercises by first revising the main theory and definitions from each part of the chapter, especially around NCERT exercises and earth questions. Start with the MCQs and assertion-reason questions to quickly test recall, then attempt the short-answer questions that need a one or two-line explanation, and finally tackle the long-answer and competency-based questions that require applying concepts to new situations. Write neat diagrams wherever the question involves a process, cycle, or setup, and always use NCERT-style vocabulary in your answers to match CBSE marking schemes.

Are these Our Home Earth: A Unique Life-Sustaining Planet questions competency-based as per NEP 2020?

Yes, the Our Home Earth: A Unique Life-Sustaining Planet exercise set follows the NEP 2020 competency-based education (CBE) framework used by CBSE and NCERT for Class 8 Science. Instead of only asking students to recall definitions, many questions are scenario-based and require applying the concept to real-life situations, analysing data, or evaluating claims. This matches Bloom's Taxonomy levels L3 (Apply), L4 (Analyse), and L5 (Evaluate), going beyond rote learning. Students practising these questions build the higher-order thinking skills that modern CBSE school exams increasingly assess, and also prepare well for competitive foundation tests in later years.

Which NCERT Curiosity sections are tested in Chapter 13 exercises?

The Chapter 13 — Our Home Earth: A Unique Life-Sustaining Planet exercise set systematically tests every major section of the NCERT Curiosity Class 8 Science textbook for this chapter. Topics covered include NCERT exercises, earth questions, atmosphere questions, conservation questions, competency-based questions. Every in-text question, activity-linked question, and end-of-chapter question from the Curiosity book is represented, so students can be confident that completing this exercise set gives them full coverage of the NCERT syllabus. Teachers also frequently pick questions from these sections for school unit tests and half-yearly exams, making thorough practice essential for strong performance.

How do assertion-reason questions work in this Class 8 Science chapter?

Assertion-reason questions in the Class 8 Science Our Home Earth: A Unique Life-Sustaining Planet exercise set present two statements — an Assertion (A) and a Reason (R) — and ask students to judge whether each is true and whether R correctly explains A. Students pick from four standard options: both true with R explaining A, both true but R not explaining A, A true and R false, or A false. This format tests whether Class 8 learners genuinely understand the cause-and-effect relationships behind NCERT exercises, not just surface facts. Mastering this format is valuable because CBSE Class 10 board exams use the same pattern.

What is the best revision strategy before attempting these exercises?

The best revision strategy before attempting Our Home Earth: A Unique Life-Sustaining Planet exercises is to read through all theory parts of NCERT Curiosity Chapter 13 once, write down the key terms such as NCERT exercises, earth questions, atmosphere questions, conservation questions, competency-based questions in your own words, and then re-do all activities mentally to understand the underlying concept. Next, make a one-page mind map linking the main ideas. Only then attempt the exercise questions — first without looking back, then self-correcting. This active-recall approach builds much stronger long-term memory than repeatedly re-reading the textbook, and is widely recommended by CBSE teachers for Class 8 Science preparation.

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Our Home Earth — Exercises

🎓 Class 8 Science CBSE Theory Ch 13 — Chemical Effects of Electric Current ⏱ ~22 min

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📚 Chapter Summary

Unique Earth

The only known planet in the solar system that supports life — thanks to a perfect combination of distance, size, atmosphere, water and magnetic field.

Goldilocks Zone

The band of distances from the Sun where liquid water can exist. Earth lies inside it at about 150 million km.

Right Size & Gravity

Earth's mass is just enough to hold its atmosphere — too small means gases escape (Mercury, Moon); too big means crushing gas layers (Jupiter).

Magnetic Shield

Generated by molten iron in Earth's outer core. Deflects solar wind, protects atmosphere and living cells from harmful radiation.

Neighbour Planets

Mercury — too hot, no air. Venus — runaway greenhouse, 465 °C. Mars — too cold, thin atmosphere, lost magnetic field.

Atmospheric Layers

Troposphere (weather) → Stratosphere (ozone) → Mesosphere (meteors) → Thermosphere (ISS, auroras) → Exosphere (boundary with space).

Air Composition

78% Nitrogen + 21% Oxygen + 1% others (Argon, CO₂, water vapour, trace gases). Tiny changes in CO₂ can cause big climate effects.

Ozone Layer

Thin layer of O₃ in the stratosphere that absorbs most harmful UV radiation. Protected under the Montreal Protocol (1987).

Water on Earth

Exists in all three states — solid, liquid, gas. 97% salty, 3% fresh; most fresh water is locked in ice or groundwater.

Extremophiles

Organisms that survive extreme heat, cold, pressure, acidity or radiation — tardigrades, Antarctic bacteria, deep-sea tube worms.

Threats

Climate change, air/water/plastic pollution, species extinction and ozone depletion — all largely caused by human activity.

Global Action

Montreal Protocol (ozone), Paris Agreement (climate), International Solar Alliance (India + France), India's 2022 single-use plastic ban.

🔑 Key Terms

Solar SystemThe Sun and the planets, moons and small bodies around it.

Goldilocks ZoneOrbital band where liquid water can exist on a planet's surface.

GravityAttractive force due to mass; holds atmosphere and keeps us on the ground.

Magnetic FieldInvisible region of magnetic force; Earth's is generated by its molten iron core.

MagnetosphereRegion around Earth shaped by its magnetic field; deflects solar wind.

Solar WindStream of high-energy charged particles from the Sun.

AtmosphereBlanket of gases surrounding Earth, held by gravity.

TroposphereLowest layer (0–12 km) where weather occurs.

Stratosphere12–50 km layer containing the ozone layer.

Mesosphere50–85 km; coldest layer where meteors burn up.

Thermosphere85–500 km; very hot but thin; auroras & ISS here.

ExosphereOutermost layer fading into space.

Ozone LayerThin O₃ layer in stratosphere that absorbs UV rays.

Greenhouse EffectHeat-trapping by gases like CO₂ and methane.

Runaway GreenhouseUncontrolled warming loop — as on Venus.

Water CycleContinuous movement of water among ocean, air and land.

ExtremophileOrganism thriving in extreme environments.

BiodiversityVariety of all living things and ecosystems.

ExtinctionPermanent disappearance of a species.

CFCsChlorofluorocarbons — gases that destroyed ozone; now banned.

Montreal Protocol1987 treaty that phased out CFCs worldwide.

Paris Agreement2015 treaty to limit global warming to below 2 °C.

ISAInternational Solar Alliance — India-led global solar initiative.

Mission LiFEIndia's lifestyle-for-environment movement.

📝 Exercises

Q1. Fill in the blanks:
(a) The region around the Sun where liquid water can exist is called the ______ zone.
(b) Earth's magnetic field protects us from the harmful ______ wind of the Sun.
(c) The ozone layer is present in the ______ layer of the atmosphere.
(d) About ______ % of Earth's total water is salty.

(a) Goldilocks / habitable (b) solar (c) stratosphere (d) 97

Q2. State True (T) or False (F):
(a) Mercury is hotter than Venus because it is closer to the Sun.
(b) Nitrogen is the most abundant gas in Earth's atmosphere.
(c) The water cycle does not operate on any other planet of our solar system.
(d) The Paris Agreement banned CFCs.

(a) F — Venus is hotter because of its runaway greenhouse effect. (b) T — nitrogen is about 78%. (c) T — Earth is the only planet with a continuous water cycle in all three states. (d) F — the Montreal Protocol (1987) phased out CFCs; the Paris Agreement (2015) targets greenhouse gases and climate change.

Q3. Explain, with reasons, why Earth is called a unique planet.

Earth is unique because it offers a rare combination of life-friendly conditions: (i) it lies in the Goldilocks zone, so liquid water is possible; (ii) its size gives just the right gravity to hold a breathable atmosphere; (iii) it has an active magnetic field that deflects the solar wind; (iv) it has an atmosphere rich in oxygen and nitrogen with a protective ozone layer; (v) water exists in all three states, driving a continuous water cycle. No other planet in the solar system has all these at once, which is why only Earth is known to support life.

Q4. Compare Venus, Earth and Mars with respect to distance from the Sun, surface temperature, atmosphere and suitability for life.

Venus — 108 million km; ~465 °C; very thick CO₂ atmosphere; runaway greenhouse makes it uninhabitable. Earth — 150 million km; average ~15 °C; thin atmosphere with N₂ + O₂; supports abundant life. Mars — 228 million km; average ~−60 °C; very thin atmosphere (mostly CO₂); liquid water unstable; no global magnetic field; currently lifeless but being explored for signs of past microbial life.

Q5. With the help of a neat labelled diagram, describe the five layers of Earth's atmosphere.

From the ground upwards: (1) Troposphere (0–12 km) — all weather; temperature falls with height. (2) Stratosphere (12–50 km) — contains ozone layer; temperature rises with height as ozone absorbs UV. (3) Mesosphere (50–85 km) — coldest layer; meteors burn up here. (4) Thermosphere (85–500 km) — very hot but thin air; ISS orbits here; auroras occur. (5) Exosphere (500+ km) — gases slowly fade into outer space; satellites orbit here. Diagram shows Earth with horizontal bands labelled with each layer and its altitude range.

Q6. How does the ozone layer protect life on Earth? What damages it, and what is being done to save it?

The ozone layer absorbs most of the Sun's ultraviolet (UV) radiation, preventing it from reaching the surface where it would cause skin cancer, eye damage, and harm tiny plankton at the base of marine food chains. It was damaged by chlorofluorocarbons (CFCs) once used in refrigerators, air-conditioners and spray cans. In 1987, almost every country signed the Montreal Protocol to phase out CFCs. Because of this global action, the ozone layer is now slowly recovering and is expected to fully heal by about 2060.

Q7. Why is fresh water called a scarce resource even though Earth is covered mostly by water?

Out of all the water on Earth, about 97% is salty seawater, unsuitable for drinking or agriculture. Only 3% is fresh water, and most of that is trapped in ice caps, glaciers or deep underground. Barely 1% of the fresh water flows in rivers and lakes where it can be used easily — less than 1% of Earth's total water. With a growing population and increasing pollution, this small share faces huge demand, making fresh water genuinely scarce.

Q8. What are extremophiles? Give two examples and explain why scientists are interested in studying them.

Extremophiles are living organisms that survive in conditions considered extreme — boiling water, polar ice, crushing deep-sea pressure, strong acid or high radiation. Examples: (i) Tardigrades — microscopic animals that survive vacuum of space, freezing and boiling. (ii) Thermophilic bacteria — microbes thriving in hot springs at 80 °C or higher. Scientists study them because (a) they expand the possibilities for finding alien life on moons like Europa and Enceladus, and (b) their special enzymes and proteins have valuable medical and industrial uses (e.g. enzymes used in COVID-19 and DNA tests).

Q9. Differentiate between the Montreal Protocol and the Paris Agreement.

Montreal Protocol (1987): targets ozone depletion; phases out CFCs and similar ozone-destroying chemicals; has largely succeeded — the ozone layer is recovering. Paris Agreement (2015): targets climate change; asks countries to cut greenhouse gas emissions (especially CO₂) to limit warming to well below 2 °C; progress is slower and continues today. In short: Montreal → ozone; Paris → climate.

Q10. List any five simple habits a student can adopt to reduce their "environmental footprint".

(i) Switch off lights, fans and chargers when not in use. (ii) Carry a reusable cloth bag and water bottle; avoid single-use plastics. (iii) Close taps while brushing; report leaks; collect rainwater. (iv) Walk or cycle for short distances; use public transport. (v) Segregate dry and wet waste; compost kitchen waste. (Also: plant trees, eat locally-grown food, avoid wasteful packaging.)

Q11. Describe two contributions of India to protecting the global environment.

(i) International Solar Alliance (ISA): Co-founded by India in 2015 with France, the ISA brings together over 100 countries to expand the use of solar energy — a clean, renewable source that does not emit greenhouse gases. (ii) Ban on single-use plastic (2022): India prohibited thin plastic bags, straws, cutlery and similar items to reduce plastic waste in landfills, rivers and oceans. Other important efforts include Mission LiFE, Project Tiger, and continued growth of forest cover.

Q12. Imagine Earth's magnetic field suddenly became extremely weak. Predict three consequences and justify each.

(i) Atmospheric loss — the solar wind would strip away the atmosphere over time, as it did on Mars; breathable air would gradually thin. (ii) Increased radiation — high-energy particles from the Sun would reach the surface, damaging DNA and increasing cancers. (iii) Disruption of migrating animals — many birds, turtles and fish use the magnetic field as a natural compass; their migration and breeding patterns would be confused. Together these would make Earth slowly less suitable for life — a reminder of how vital this invisible shield is.

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