Class 8 Science · Chapter 13
Short answer:
NCERT Class 8 Science Curiosity, Chapter 13 "Our Home: Earth, a Unique Life Sustaining Planet" hume batata hai ki Earth solar system ka woh akela planet kyun hai jahan life exist karti hai — sahi distance from Sun, atmosphere, water, aur temperature range ka combination. Ye naye rationalised 13-chapter Class 8 Science Curiosity textbook ka last chapter hai (2026-27 session).
Chapter 1 se lekar Chapter 12 tak humne matter, forces, light, electricity aur nature ke systems padhe — is last chapter "Our Home: Earth, a Unique Life Sustaining Planet" me hum zoom-out karte hain aur poore solar system ke context me Earth ko dekhte hain. Ye chapter samjhata hai ki Earth ko "unique" kyun kaha jata hai — iski position, atmosphere, temperature, water availability, aur gravity ka ek perfect combination jo life ko possible banata hai.
Ye chapter poore class 8 science curiosity book ka conceptual closure hai — jaise Chapter 1 ne matter ki neev rakhi thi (particulate nature of matter), waise hi ye chapter Earth Science ki neev rakhta hai jo Class 9-10 me Geography/Environmental Science se connect hogi. School exams me is chapter se diagram-based, comparison-table-based aur "why Earth is unique" type reasoning questions common hain.
Chapter 13 Summary — 5 Minute Revision
Is chapter me hum padhte hain ki solar system me Sun ke around 8 planets ghoomte hain, lekin sirf Earth par hi confirmed life hai. Iske peeche 4 major reasons hain:
1. Right distance from Sun: Earth na zyada paas hai (jaise Mercury/Venus, jo bohot garam hain) na zyada door (jaise Mars se aage ke planets, jo bohot thande hain). Is ideal zone ko "Habitable Zone" ya "Goldilocks Zone" bolte hain — na zyada garam, na zyada thanda, "just right".
2. Presence of Atmosphere: Earth ka atmosphere mainly nitrogen (~78%) aur oxygen (~21%) se bana hai, thoda carbon dioxide aur dusri gases bhi hain. Ye breathing ke liye zaroori hai, harmful UV radiation ko rokta hai (ozone layer), aur temperature ko regulate karta hai (greenhouse effect ka balanced form).
3. Availability of Water in liquid form: Earth ka lagbhag 71% surface water se dhaka hai. Sirf Earth par hi water teeno states (solid, liquid, gas) me naturally exist karta hai. Liquid water life ke liye essential solvent hai — isiliye solutes solvents and solutions class 8 wala concept yahan biologically bhi important ho jata hai, kyunki cells ke andar ki reactions water-based solutions me hoti hain.
4. Suitable Temperature Range aur Gravity: Earth ka average surface temperature life-friendly hai, aur Earth ki gravity itni strong hai ki atmosphere ko bandhe rakhe (Moon jaisa nahi jahan gravity kam hai aur atmosphere escape kar gaya).
Chapter me Earth ki internal structure (crust, mantle, core) aur layers of atmosphere (troposphere, stratosphere, etc.) ka bhi basic overview milta hai, saath hi ye bhi discuss hota hai ki human activities (pollution, deforestation, global warming) is delicate balance ko kaise disturb kar rahi hain — isliye chapter ka closing message conservation aur responsible behaviour par hota hai.
Interesting cross-link: Chapter 12 "how nature works in harmony class 8" me humne food chains aur ecosystems padhe the — ye chapter uss harmony ko planetary scale par extend karta hai: Earth khud ek balanced system hai jisme atmosphere, hydrosphere, lithosphere aur biosphere ek dusre ko support karte hain.
In-Text Questions — Solutions
Earth ko 'unique planet' kyun kaha jata hai?
Earth ko unique isliye kaha jata hai kyunki ye solar system ka aisa planet hai jahan life exist karne ke liye zaroori sabhi conditions ek saath maujood hain: (1) Sun se sahi distance (Habitable Zone me), (2) breathable atmosphere jisme oxygen aur nitrogen hai, (3) liquid water ki abundant availability (~71% surface), aur (4) life-supporting temperature range (average ~15°C, na zyada garam na zyada thanda). Koi aur confirmed planet in sab conditions ko ek saath satisfy nahi karta.Habitable Zone kya hoti hai?
Habitable Zone (jise Goldilocks Zone bhi bolte hain) Sun ke around woh region hai jahan koi planet ho to uska temperature na itna zyada ho ki water turant evaporate ho jaaye, na itna kam ho ki water hamesha frozen rahe. Is zone me hi liquid water surface par stable reh sakta hai. Earth is zone ke bilkul beech me hai — Venus zone se andar (bahut garam) hai aur Mars zone se bahar ki taraf (bahut thanda) hai.Earth ke atmosphere ki composition kya hai aur ye life ke liye kyun zaroori hai?
Earth ke atmosphere me approximately Nitrogen 78%, Oxygen 21%, aur baaki 1% me Carbon dioxide, Argon aur trace gases hain. Ye zaroori isliye hai kyunki: Oxygen respiration ke liye chahiye, Nitrogen plant growth (proteins) ke liye zaroori hai, Carbon dioxide photosynthesis me use hoti hai, aur ozone layer (stratosphere me) harmful UV radiation se surface ko protect karti hai. Atmosphere temperature ko bhi ek reasonable range me maintain karta hai.Exercise Questions — Solutions (Q1–Q4)
Solar system ke sabhi planets me se sirf Earth par hi life kyun sambhav hai? Chaar reasons detail me likho.
Step-by-step answer (4 marks — 1 mark per reason):
1. Sahi distance from Sun (1 mark): Earth Habitable Zone me sthit hai — Sun se na bahut paas (jaise Mercury, jahan din ka temperature 400°C+ ho sakta hai) na bahut door (jaise outer planets, jahan temperature -100°C se bhi neeche chala jata hai). Isse Earth ka average temperature life-friendly rehta hai.
2. Suitable Atmosphere (1 mark): Earth ka atmosphere Nitrogen (78%) aur Oxygen (21%) se bana hai jo breathing, photosynthesis aur protection (ozone layer) provide karta hai.
3. Availability of Water (1 mark): Earth ka ~71% part water se dhaka hai, jo teeno states (solid — ice, liquid — oceans, gas — water vapour) me exist karta hai. Liquid water life ki basic requirement hai.
4. Suitable Gravity aur Temperature Range (1 mark): Earth ki gravity atmosphere ko surface se bandhe rakhti hai (escape nahi hone deti), aur average surface temperature (~15°C) life-processes ke liye ideal hai.
Earth ki internal structure ke teen major layers ke naam likho aur unka ek-ek characteristic batao.
Step-by-step answer (3 marks):
1. Crust: Earth ki sabse upar wali, sabse patli (thin) layer hai, jispar hum rehte hain. Ye solid rocks aur soil se bani hoti hai.
2. Mantle: Crust ke neeche wali mota (thick) layer hai, semi-solid/molten rock (magma) se bani hoti hai, aur Earth ke volume ka sabse bada hissa cover karti hai.
3. Core: Earth ka sabse andar wala hissa hai, do parts me — outer core (liquid, mainly iron-nickel) aur inner core (solid, extreme high pressure ki wajah se) me divide hota hai. Core Earth ke magnetic field ke liye responsible hai.
Global warming aur human activities Earth ke life-supporting balance ko kaise disturb kar rahi hain? Do examples do.
Step-by-step answer (2 marks):
Example 1 — Deforestation aur CO2 increase: Jab hum forests kaatte hain aur fossil fuels (coal, petroleum) jalaate hain, atmosphere me carbon dioxide badh jata hai. Ye extra CO2 greenhouse effect ko badhata hai, jisse Earth ka average temperature dheere-dheere badh raha hai (global warming), jo ice caps ko pighla raha hai aur weather patterns disturb kar raha hai.
Example 2 — Pollution of water aur air: Industrial waste aur vehicles se nikalne wale pollutants water bodies aur atmosphere ki quality kharab karte hain, jisse dono humans aur dusre organisms ke survival par negative impact padta hai — isse ecosystem ka natural balance (jo Chapter 12 me 'how nature works in harmony' me padha tha) disturb hota hai.
Numerical/data-based: Agar Earth ka total surface area 510 million km² hai aur usme se 71% water se dhaka hai, to land area kitni hai?
Water-covered area = 71% of 510 million km²
= (71/100) × 510 = 362.1 million km²
Land area = Total area − Water area = 510 − 362.1 = 147.9 million km²
Answer: Earth ka land area approximately 147.9 million km² hai (~29%).
Important Equations — Ek Nazar Me
| Concept | Key Point / Relation |
|---|---|
| Habitable Zone condition | Not too hot, not too cold — liquid water surface par stable rehta hai |
| Earth's atmosphere composition | Nitrogen ≈ 78%, Oxygen ≈ 21%, Other gases (CO₂, Argon, etc.) ≈ 1% |
| Water coverage on Earth | Approx. 71% surface water, 29% land |
| Earth's internal layers | Crust (thin, outermost) → Mantle (thick, middle) → Core (innermost, outer liquid + inner solid) |
| Average surface temperature | Approximately 15°C — life-supporting range |
| Water-area calculation | Water area = (% water ÷ 100) × Total surface area |
↔ Table ko side me swipe karein
Common Mistakes — Yahan Marks Kat te Hain
- Students Habitable Zone ko sirf 'Earth ke around ka area' samajh lete hain — actually ye Sun ke around ek specific distance-range hai jahan koi bhi planet ho to liquid water possible ho.
- 'Atmosphere hai' aur 'breathable atmosphere hai' me farak nahi karte — Venus aur Mars dono me atmosphere hai lekin wo life-supporting composition ka nahi hai (mostly CO2).
- Earth ke 71% water ko sab 'drinkable/freshwater' samajh lete hain — jabki isme se zyadatar (~97%) oceans ka saltwater hai, sirf thoda fraction freshwater hai.
- Crust, Mantle, Core ka order galat likh dete hain ya inki thickness ka sahi sense nahi hota — Mantle sabse thick layer hai, Crust sabse patli.
- Global warming aur Greenhouse effect ko same cheez samajh lete hain — Greenhouse effect naturally zaroori hai (Earth ko warm rakhta hai), Global warming iska excessive/harmful increase hai human activities ki wajah se.
- Numerical questions me percentage calculate karte waqt total area ko formula me galat jagah rakh dete hain — hamesha (% ÷ 100) × Total likhna yaad rakho, seedha % ko multiply mat karo.
Board-Style Important Questions
- School/board-pattern question: 'Explain why Earth is called a unique planet in our solar system' (reasoning-based question type)
- Diagram-based question: 'Label the internal structure of Earth showing Crust, Mantle and Core' (diagram-labeling question type)
- Comparison-based question: 'Compare Earth's atmosphere with that of Venus or Mars and explain why Earth supports life' (comparison/HOTS-style question type)
- Assertion-Reason style question based on statements about Habitable Zone and liquid water availability (competency-based question type)
- Very short answer: 'What percentage of Earth's surface is covered with water?' (factual recall question type)
Aksar Poochhe Jaane Wale Sawaal
NCERT Class 8 Science Curiosity chapter 1 solutions is website par milenge kya?
Haan, ye site poore Class 8 Science Curiosity textbook (all 13 chapters) ke solutions cover karti hai, jisme Chapter 1 se leke Chapter 13 'Our Home: Earth' tak sab shaamil hain — har chapter ke intext questions, exercise questions, aur exam-style answers ke saath.
Class 8 Science Curiosity book PDF download 2026-27 session ke liye kaha se milegi?
Official NCERT textbook PDF NCERT ki official website (ncert.nic.in) se free download ki ja sakti hai. Solutions aur explanations ke liye is jaisi study resources use karo, lekin original textbook content hamesha official NCERT source se hi verify karo.
Kya ye chapter (Our Home: Earth) purane syllabus ke 'Stars and Solar System' chapter jaisa hai?
Nahi, ye purane chapter se different hai. Old NCERT me 'Stars and Solar System' astronomy-focused tha (stars, constellations, planets ki details), jabki ye naya chapter Earth-centric hai — specifically ye samjhata hai ki Earth life ko support karne ke liye kyun unique hai, na ki sirf solar system ki general jaankari deta hai.
Is chapter se related dusre chapters kaunse hain jo revise karne chahiye?
Chapter 12 'How Nature Works in Harmony' (food chains, ecosystems) is chapter se directly connect hota hai. Chapter 1 (particulate nature of matter) aur Chapter 7 (solutes, solvents and solutions) bhi conceptually related hain kyunki water ka role (solvent) discuss hota hai. Revision ke liye ye teeno chapters saath padhna helpful rahega.
Kya is chapter se numerical questions aate hain?
Ye chapter mainly conceptual/descriptive hai, lekin school tests me simple percentage-based calculations (jaise water-covered area vs land area) puchhe ja sakte hain — jaise exercise section me diya gaya numerical example.
Health the ultimate treasure aur is chapter ka koi connection hai kya?
Directly nahi, lekin dono chapters ek broader theme share karte hain — 'balance' ka concept. 'Health the Ultimate Treasure' human body ke internal balance (health) par focus karta hai, jabki ye chapter planetary-scale balance (Earth's ecosystem) par — dono me disturbance (bimari ya pollution) se system disturb hota hai, ye common thread exam-answers me bhi likha ja sakta hai agar analogy-based question aaye.
Class 8 Science — Saare Chapters
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