NCERT
Every NCERT book that matters for UPSC — open a book, then a chapter. Learn each chapter's concepts, then how UPSC tests them — with diagrams, flowcharts and the past questions to attempt.
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← Fundamentals of Physical Geography — all chaptersThe Origin and Evolution of the Earth
Start here: why this chapter matters
In simple wordsEvery family has a story of where it came from. This chapter is the earth's family story — starting long before the earth, with the birth of the universe, then stars, then planets, and finally how one hot, lifeless ball of rock became a planet with air, oceans and life.
Chapter 1 told you what geography studies. This chapter goes back to the very beginning: how the stage itself — the earth — was built. It answers four questions in order: How did the universe begin? How did stars and planets form? How did the earth get its layers? How did air, water and life appear? Each answer is the starting point of a later chapter.
- Opens Unit II, ‘The Earth’ — the unit that goes on to the earth's interior, continental drift and plate tectonics, earthquakes and volcanoes.
- Leads into Chapter 3 (Interior of the Earth): the layers made here by ‘differentiation’ are studied there.
- Links to Chapter 7 (Composition and Structure of Atmosphere) — today's nitrogen–oxygen air is the end of the story told here.
- UPSC: Prelims asks it under both Geography and Science & Technology (Big Bang, light year, nebulae); Mains GS1 asked about the origin of the earth through a space mission (2017).
| Word | What it means here |
|---|---|
| Universe | Everything that exists — all space, matter and energy |
| Galaxy | A huge system of a very large number of stars (ours is the Milky Way) |
| Nebula | A very large cloud of gas (mostly hydrogen) and dust in space; plural nebulae |
| Light year | The distance light travels in one year — a unit of distance |
| Planetesimal | A small rounded body in the early solar system; many joined to make a planet |
| Accretion | Growing bigger by small pieces sticking together |
| Density | How much mass is packed into a given volume — iron is denser than rock |
| Differentiation | Separation of the earth's materials into layers by density |
| Primordial | Existing at the very beginning |
| Degassing | Gases escaping from the earth's interior to the surface |
| Photosynthesis | Plants and algae making food from sunlight, water and carbon dioxide — releasing oxygen |
At a glance — the six ideas to carry away
- Nebular hypothesis (Kant → Laplace 1796 → Schmidt & Weizsäcker 1950): planets from a rotating cloud round a young sun.
- Big Bang = expanding universe: a singularity exploded 13.7 billion years ago; space between galaxies keeps growing.
- A light year is a distance (≈ 9.461 × 10¹² km), not a unit of time.
- Planets: gas core + disc → planetesimals → a few large planets by accretion.
- The earth became layered by differentiation: heavy iron sank, light material rose.
- Atmosphere in 3 stages: solar winds stripped H–He → degassing → photosynthesis added oxygen.
1. Early theories: the nebular hypothesis
In simple wordsStir a cup of tea with a few tea leaves in it. The liquid spins, and the leaves gather together as they swirl. The nebular idea is similar: a slowly spinning cloud of gas and dust around a young sun, whose material gathered into planets.
Many philosophers and scientists offered ideas about how the earth was born. One of the early and popular ones came from the German philosopher Immanuel Kant; the mathematician Laplace revised it in 1796. This is the Nebular Hypothesis: the planets formed from a cloud of material associated with a youthful sun that was slowly rotating.
In 1950, Otto Schmidt (Russia) and Carl Weizsäcker (Germany) revised the idea, though they differed in details. In their version the sun was surrounded by a solar nebula of mostly hydrogen and helium plus dust. Friction and collision of particles made a disc-shaped cloud, and the planets formed by accretion. Later scientists turned to a bigger question — the origin of the whole universe, not just the earth.
⤵ How the explanation grew
Kant — Nebular Hypothesisplanets from a rotating cloud round a young sun
Laplace revises it — 1796still an explanation of the earth and planets only
Schmidt (Russia) and Weizsäcker (Germany) — 1950solar nebula of H, He and dust → disc → planets by accretion
Modern theoriesthe question widens to the origin of the whole universe → the Big Bang
Beyond NCERTKant published his idea in 1755. The usual spelling of the German scientist's name is Carl Friedrich von Weizsäcker (NCERT prints ‘Weizascar’). Other old theories you may meet in older books — Chamberlin and Moulton's planetesimal hypothesis and James Jeans's tidal hypothesis — imagined a passing star pulling material out of the sun; they are no longer accepted.
Exam trapUPSC 1999 asked which scholar suggested the earth's origin from gases and dust particles: the answer was O. Schmidt — not James Jeans, Alfvén or Hoyle. Hoyle is linked to the steady state theory (section 2).
2. The Big Bang: how the universe began
In simple wordsImagine running a film of the universe backwards. Galaxies that are now far apart come closer and closer, until everything is squeezed into one unimaginably small, hot point. Run the film forwards from that point and you have the Big Bang — not an explosion in space, but space itself starting to grow.
The most popular explanation of the universe's origin is the Big Bang Theory, also called the expanding universe hypothesis. Edwin Hubble (1920, as NCERT puts it) gave evidence that the universe is expanding: as time passes, galaxies move further and further apart.
Reading NCERT Figure 2.1 — The Big Bang (page 14)
- It is an upside-down cone: the point at the bottom is the only label — ‘Singularity’. Time runs upwards.
- Just above the point is a burst — the bang — and then three slices of the universe, each wider than the one below. The widening cone is the expansion.
- Each slice holds galaxies (drawn as spirals): about three in the lowest slice, four in the middle, five in the top one, and they are farther apart in each later slice.
- Notice: the book also draws the galaxies bigger in later slices. The text itself warns that galaxies do not expand — only the space between them grows (the same flaw it points out in the balloon example). Our re-drawing keeps the galaxies the same size.
- The figure has no dates or numbers: learn them from the text — 13.7 billion years, 3 minutes, 300,000 years, 4,500 K.
⤵ Stages of the Big Bang (NCERT)
(i) Singularityall matter in one place — a ‘tiny ball’ of tiny volume, infinite temperature and density
(ii) The Big Bang — 13.7 billion years agoviolent explosion → huge expansion, fastest in the first fractions of a second, slower since; still going on
Energy → matteras it grew, some energy became matter; the first atom began to form within the first three minutes
(iii) Within 300,000 yearstemperature fell to 4,500 K → atomic matter; the universe became transparent
The balloon experiment. Mark dots on a balloon (the galaxies) and blow it up: the dots move away from one another, just as galaxies do. But the dots also grow as the rubber stretches — and real galaxies do not. Scientists observe that the space between galaxies increases, but galaxies themselves do not expand. So the balloon example is only partly correct.
| Big Bang (expanding universe) | Steady state | |
|---|---|---|
| Proposed / backed by | Evidence from Edwin Hubble that galaxies are moving apart | Fred Hoyle |
| Idea | The universe began at one moment and has been expanding ever since | The universe is roughly the same at any point of time |
| Status today | Favoured by the scientific community | Given up as evidence for expansion grew |
Beyond NCERT — the numbers scientists use today
- Age of the universe: about 13.8 billion years (NCERT's 13.7 is the older estimate).
- Hubble's landmark paper showing galaxies racing away (the farther, the faster — Hubble's law) came in 1929; the ‘1920’ in NCERT is approximate.
- What formed in the first three minutes were the nuclei of light elements (hydrogen, helium); complete, neutral atoms formed at about 380,000 years, when the universe had cooled to roughly 3,000 K and light could travel freely. That leftover light is the cosmic microwave background.
- The two main evidences for expansion are the red shift of light from distant galaxies and the cosmic microwave background — exactly what UPSC asked in 2012.
- Fred Hoyle proposed the steady state theory with Hermann Bondi and Thomas Gold (1948); ironically, Hoyle coined the name ‘Big Bang’ while mocking it.
Exam trapThe expanding universe is about space between galaxies increasing — not galaxies growing. And Hubble = expansion of the universe; Wegener = continental drift (UPSC 2008 swapped them to trap you).
3. Galaxies, stars and the light year
In simple wordsSprinkle flour unevenly on a table and blow gently: the flour gathers into small heaps where there was a little more to begin with. In the early universe, places with slightly more matter had slightly more gravity, pulled in more matter, and grew into galaxies and stars.
⤵ From uneven matter to stars
Matter and energy unevenly spreadsmall density differences in the early universe
Differences in gravitational forcematter is drawn together where gravity is stronger
Galaxies begina galaxy starts as a huge cloud of hydrogen — a nebula
Nebula forms localised clumpsclumps grow into denser and denser gas bodies
Stars are bornNCERT: star formation about 5–6 billion years ago
- A galaxy contains a very large number of stars.
- Galaxies are spread over distances measured in thousands of light years.
- Diameters of individual galaxies: 80,000–150,000 light years.
Reading the light-year box (page 14)
- A light year is a measure of distance, not of time.
- Light travels at 300,000 km per second; in a year it covers 9.461 × 10¹² km (the reprint has lost the ‘×’ sign and prints ‘9.461 10¹²’).
- Mean sun–earth distance: 149,598,000 km. The box says ‘in terms of light years, it is 8.311 minutes’ — read this as 8.311 light-minutes: light from the sun takes about 8.3 minutes to reach us. (149,598,000 ÷ 300,000 ≈ 499 seconds ≈ 8.3 minutes — the arithmetic checks out; only the unit wording is loose.)
Beyond NCERT
- NCERT's ‘5–6 billion years ago’ for star formation should not be read as the age of the first stars: the first stars lit up within the first few hundred million years after the Big Bang, and stars are still forming today. Our sun is about 4.6 billion years old — the same age as the earth.
- Light from the moon takes about 1.3 seconds; from the nearest star beyond the sun (Proxima Centauri) about 4.2 years.
- Astronomers use light years because the speed of light is constant (UPSC 2021). Other space objects asked in 2023: Cepheids — stars that brighten and dim regularly; pulsars — spinning neutron stars left after massive stars collapse.
Exam trapA light year measures distance. A nebula is a giant cloud of gas and dust — not a star that brightens and dims (that is a Cepheid). UPSC 2023 swapped exactly these two descriptions.
4. How the planets formed
In simple wordsRoll a small ball of wet snow across a snowy field: it picks up more snow and grows into a big snowball. Planets grew the same way — tiny grains stuck together into small bodies, and small bodies crashed and stuck together into a few big ones.
| Stage | What happens | Key word |
|---|---|---|
| (i) | Stars are local lumps of gas inside a nebula. Gravity inside a lump forms a core, and a huge rotating disc of gas and dust develops round it | Core and disc |
| (ii) | The gas cloud condenses; matter round the core becomes small rounded objects, which grow by cohesion into planetesimals. Collisions and gravity make the material stick into larger bodies | Planetesimals |
| (iii) | The many small planetesimals accrete to form a few large bodies — the planets | Accretion |
Connect the ideasThe planet-forming disc of stage (i) is the same disc-shaped cloud of the revised nebular hypothesis (Schmidt and Weizsäcker). The modern picture keeps that idea and places it inside the bigger Big Bang story.
Exam trapOrder matters: disc → planetesimals → planets. Planetesimals are many small bodies; planets are few large ones.
5. Evolution of the earth: the layered lithosphere
In simple wordsShake a jar of water with sand, pebbles and a little oil, then leave it. The pebbles sink to the bottom, the sand settles above them, and the oil floats on top. The young earth, hot and soft, sorted itself the same way: heavy at the centre, light at the surface.
The young earth was very different from today's: a barren, rocky and hot object with a thin atmosphere of hydrogen and helium. Over the period from 4,600 million years ago to the present, a chain of processes turned it into a planet with plenty of water, a life-friendly atmosphere and life itself.
The earth has a layered structure: from the outer edge of the atmosphere to the centre, material is not uniform. Air has the least density; inside the earth there are zones with different materials. NCERT asks: how did these layers develop?
⤵ How the layers formed
Primordial earth: mostly volatilehot and largely in a fluid, unsettled state
Density and temperature inside increasematerial starts separating by density
Heavy materials (iron) sink; light ones risethis sorting is called differentiation
The earth cools, solidifies and shrinksthe outer surface forms a crust
Giant impact forms the moonthe earth is heated up again
Layers: crust → mantle → outer core → inner coredensity increases from the crust to the core (details in Chapter 3)
Reading the question box on page 15The grey box asks: ‘How was the layered structure of the earth developed?’ The answer is the next paragraph — differentiation, helped by the heat of the moon-forming giant impact. NCERT's exercise question 2(i) asks you to explain this process.
Beyond NCERTThe moon is thought to have formed about 4.5 billion years ago, when a Mars-sized body (often called Theia) struck the young earth; debris thrown into orbit gathered into the moon. NCERT mentions the giant impact only as a source of extra heat.
Exam trapDifferentiation made the earth's layers; it is not one of the processes that formed the atmosphere (NCERT exercise Q1-ii). The atmosphere's processes are solar winds, degassing and photosynthesis.
6. Evolution of the atmosphere and the oceans
In simple wordsThink of a pot of rice on the stove. First the lid is blown off (the first air is lost). Then steam rises from inside the pot (gases come out of the hot earth). The steam cools on the lid and drips back as water (rain fills the oceans). Last, someone adds fresh herbs that change the smell (living things add oxygen).
Today's atmosphere is mainly nitrogen and oxygen. It reached that state in three stages:
⤵ The three stages of the atmosphere
Stage 1 — Loss of the primordial atmospherethe first hydrogen–helium air was stripped away by solar winds (on all terrestrial planets)
Stage 2 — The hot interior adds gases (degassing)as the earth cooled, water vapour, nitrogen, CO2, methane, ammonia came out; very little free oxygen; volcanoes kept adding more
Water vapour condensesCO2 dissolves in rain; cooling → more rain
Oceans formin depressions, within 500 million years of the earth's birth
Life begins in the oceansabout 3,800 million years ago
Photosynthesis evolves2,500–3,000 million years ago
Stage 3 — Life modifies the air (photosynthesis)oceans saturated with oxygen; about 2,000 million years ago oxygen began to flood the atmosphere
| Early atmosphere (after degassing) | Present atmosphere |
|---|---|
| Water vapour, nitrogen, carbon dioxide, methane, ammonia; very little free oxygen | Mainly nitrogen and oxygen |
| Supplied by the hot interior and volcanoes | Oxygen supplied by photosynthesis of living things |
- Solar wind — the stream of charged particles from the sun — removed the first, light H–He atmosphere.
- Degassing is the name for gases pouring out of the earth's interior.
- Oceans formed within 500 million years of the earth's formation, so they are about 4,000 million years old.
- Life stayed confined to the oceans for a long time.
Beyond NCERTGeologists call the rise of oxygen in the air the Great Oxidation Event, usually dated to about 2.4 billion years ago; NCERT gives a round 2,000 million years. Oxygen in the air later allowed the ozone layer to form, which shielded land from ultraviolet rays so that life could move out of the oceans. UPSC 2018 tested this chapter's idea directly: the early atmosphere was not oxygen-rich, and living organisms did modify it.
Exam trapThe first atmosphere (H, He) was lost to solar winds — it is not the source of today's air. Today's air began with degassing, and its oxygen came from photosynthesis, not from volcanoes.
NCERT says ‘Chapter 8’The text says the composition and structure of the atmosphere are dealt with in ‘Chapter 8’. In the current book that is Chapter 7 (Composition and Structure of Atmosphere); Chapter 8 is Solar Radiation, Heat Balance and Temperature.
7. Origin of life
In simple wordsLego bricks lying in a box are not a house. Put them together in the right way and you get a structure — and if that structure could build copies of itself, it would be ‘alive’. Scientists think life began like that: simple chemicals joined into complex molecules that could copy themselves.
The last phase of the earth's evolution is the origin and evolution of life. At first neither the earth nor its atmosphere suited life. Modern scientists see the origin of life as a kind of chemical reaction: it first produced complex organic molecules and assembled them so that they could duplicate themselves — turning non-living matter into living substance.
⤵ From chemicals to the fossil record
Simple chemicals in the early oceansa world not yet suited to life
Complex organic molecules formthrough chemical reactions
Molecules assemble and copy themselvesinanimate matter becomes living substance — about 3,800 million years ago
Life leaves traces in rocks as fossilsmicroscopic structures like blue algae, in rocks older than 3,000 million years
Beyond NCERT
- ‘Blue algae’ are today called cyanobacteria (blue-green algae). They were among the first organisms to photosynthesise, so they produced the oxygen of section 6.
- The oldest widely accepted fossils are stromatolites — layered mounds built by such microbes — about 3.5 billion years old.
- The elements at the heart of living molecules are carbon, hydrogen, nitrogen and oxygen.
| Geological time (Beyond NCERT, rounded) | When | What to remember |
|---|---|---|
| Hadean eon | 4,600–4,000 Ma | Earth and moon form; first oceans |
| Archaean eon | 4,000–2,500 Ma | First life; earliest fossils; photosynthesis begins |
| Proterozoic eon | 2,500–about 540 Ma | Oxygen builds up in the air; first many-celled life |
| Phanerozoic eon — Palaeozoic era | about 540–252 Ma | Life spreads onto land; fishes, amphibians, early reptiles |
| Mesozoic era | 252–66 Ma | Age of dinosaurs; ends with a mass extinction |
| Cenozoic era | 66 Ma–today | Age of mammals; humans appear very late |
Exam trapLife appeared about 3.8 billion years ago — not 3.8 million (NCERT exercise Q1-iii). The earth is 4.6 billion years old; the universe 13.7 billion (NCERT).
NCERT exercise — answer outlines
The three multiple-choice questions are in the Self-check below. Try each written question yourself first, then open the outline to compare. These are the points an examiner looks for.
2(i) What is meant by the process of differentiation? (30 words)
The separation of the young earth's materials into layers according to density. As the hot, volatile earth heated up inside, heavier materials like iron sank to the centre and lighter ones rose, giving crust, mantle, outer core and inner core.
2(ii) What was the nature of the earth surface initially? (30 words)
Barren, rocky and hot, with a thin atmosphere of hydrogen and helium; mostly volatile in its primordial stage. There was no water body, no oxygen-rich air and no life.
2(iii) What were the gases which initially formed the earth's atmosphere? (30 words)
The primordial atmosphere: hydrogen and helium (stripped by solar winds). After degassing, the early atmosphere had water vapour, nitrogen, carbon dioxide, methane, ammonia and very little free oxygen.
3(i) Write an explanatory note on the ‘Big Bang Theory’. (150 words)
Intro: the most accepted theory of the origin of the universe, also called the expanding universe hypothesis; Edwin Hubble showed galaxies are moving apart.
Stages: (i) all matter in a singularity — tiny volume, infinite temperature and density; (ii) it exploded 13.7 billion years ago → enormous, very rapid expansion, slowing later; energy turned into matter; the first atom within three minutes; (iii) within 300,000 years the temperature fell to 4,500 K → atomic matter; universe became transparent.
Meaning of expansion: the space between galaxies grows — the balloon analogy (only partly right, since galaxies don't expand).
Alternative: Hoyle's steady state — universe the same at all times — rejected as evidence for expansion grew.
After: uneven matter → galaxies → stars → planets.
Diagram: a quick cone like Figure 2.1 earns marks.
Stages: (i) all matter in a singularity — tiny volume, infinite temperature and density; (ii) it exploded 13.7 billion years ago → enormous, very rapid expansion, slowing later; energy turned into matter; the first atom within three minutes; (iii) within 300,000 years the temperature fell to 4,500 K → atomic matter; universe became transparent.
Meaning of expansion: the space between galaxies grows — the balloon analogy (only partly right, since galaxies don't expand).
Alternative: Hoyle's steady state — universe the same at all times — rejected as evidence for expansion grew.
After: uneven matter → galaxies → stars → planets.
Diagram: a quick cone like Figure 2.1 earns marks.
3(ii) List the stages in the evolution of the earth and explain each stage in brief. (150 words)
Intro: 4,600 million years ago the earth was barren, rocky and hot with a thin H–He atmosphere.
1. Lithosphere — differentiation: heavy iron sank, light material rose; cooling formed the crust; the moon-forming giant impact reheated the earth; layers crust → mantle → outer core → inner core.
2. Atmosphere — three stages: (a) the primordial H–He air was stripped by solar winds; (b) degassing and volcanoes released water vapour, N₂, CO₂, CH₄, NH₃; (c) photosynthesis added oxygen, which flooded the air about 2,000 million years ago.
3. Hydrosphere: vapour condensed, CO₂ dissolved in rain, more cooling, more rain → oceans within 500 million years (~4,000 million years old).
4. Life: chemical reactions made self-copying organic molecules about 3,800 million years ago; blue-algae-like fossils older than 3,000 million years.
Conclude with a timeline sketch.
1. Lithosphere — differentiation: heavy iron sank, light material rose; cooling formed the crust; the moon-forming giant impact reheated the earth; layers crust → mantle → outer core → inner core.
2. Atmosphere — three stages: (a) the primordial H–He air was stripped by solar winds; (b) degassing and volcanoes released water vapour, N₂, CO₂, CH₄, NH₃; (c) photosynthesis added oxygen, which flooded the air about 2,000 million years ago.
3. Hydrosphere: vapour condensed, CO₂ dissolved in rain, more cooling, more rain → oceans within 500 million years (~4,000 million years old).
4. Life: chemical reactions made self-copying organic molecules about 3,800 million years ago; blue-algae-like fossils older than 3,000 million years.
Conclude with a timeline sketch.
Project work: NASA's ‘Stardust’ project — which agency, why collect stardust, and from where?
Beyond NCERT: (i) NASA (USA) launched the Stardust spacecraft in 1999. (ii) Comet and interstellar dust is almost unchanged material from the time the solar system formed, so it tells scientists what the early solar nebula was made of — the raw material of the planets in this chapter. (iii) It collected particles from the tail (coma) of Comet Wild 2 in 2004, plus interstellar dust, in a gel called aerogel, and returned them to earth in a capsule that landed in Utah, USA, in January 2006. (The web addresses printed in the book are out of date.)
What to remember
Numbers
Laplace revises the nebular hypothesis1796
Schmidt and Weizsäcker revise it1950
Hubble's evidence of expansion (NCERT)1920
Big Bang (NCERT)13.7 billion years ago
First atom began to formwithin 3 minutes
Universe transparent; atomic matterwithin 300,000 years, at 4,500 K
Diameter of a galaxy80,000–150,000 light years
Star formation (NCERT)5–6 billion years ago
Speed of light300,000 km/s
1 light year9.461 × 10¹² km
Mean sun–earth distance149,598,000 km ≈ 8.3 light-minutes
Age of the earth4,600 million years
Oceans formedwithin 500 million years → ~4,000 million years old
Life began~3,800 million years ago
Blue-algae-like fossilsolder than 3,000 million years
Photosynthesis evolved2,500–3,000 million years ago
Oxygen floods the atmosphere~2,000 million years ago
Stages of the atmosphere3
One-liners
- Nebular hypothesis: Kant → Laplace (1796) → Schmidt & Weizsäcker (1950).
- Big Bang = expanding universe hypothesis; evidence from Edwin Hubble.
- Steady state = Hoyle: the universe is roughly the same at all times.
- A galaxy begins as a nebula — a huge cloud of hydrogen gas.
- Light year = a distance.
- Planets: core and disc → planetesimals → accretion.
- Differentiation made the layers; density rises from crust to core.
- Atmosphere: solar winds → degassing → photosynthesis.
- Life was confined to the oceans for a long time.
Traps to avoid
- A light year measures distance, not time.
- The universe expands by the space between galaxies growing; galaxies themselves do not expand.
- Hubble = expanding universe; Wegener = continental drift; Hoyle = steady state; Schmidt = earth from gas and dust.
- Differentiation formed the earth's layers — it did not form the atmosphere.
- The first (H–He) atmosphere was lost to solar winds; today's air began with degassing.
- The early atmosphere had very little free oxygen; oxygen came from photosynthesis.
- Life: 3.8 billion years ago — not million. Earth: 4.6 billion. Universe: 13.7 billion (NCERT).
- Planetesimals are many small bodies; planets are few large ones.
- A nebula is a gas-and-dust cloud; a star that brightens and dims regularly is a Cepheid.
How to strategise
Prelims — what UPSC asks
- Asked under two subjects. Geography asks the earth's story — who said the earth formed from gas and dust (Schmidt, 1999), how the early atmosphere changed (2018). Science & Technology asks the universe — Hubble and expansion (2008), the evidence for expansion (microwave background, red shift — 2012), nebulae, Cepheids and pulsars (2023).
- The light-year box is a favourite: the unit for star distances (1980) and why astronomers use it — the speed of light is constant (2021).
- Match-the-scientist questions recur: learn Kant, Laplace, Schmidt, Weizsäcker, Hubble, Hoyle, Wegener as one list.
- Statement questions twist the order or the gas — e.g. ‘the early earth had 54% oxygen’ (false, 2018). Know which gases came first, and that oxygen came last.
- Follow space news on the origin of the solar system (comet and asteroid sample missions, planetary probes) — UPSC links them back to this chapter.
Mains — where it appears and how to answer
- GS1 (Geography): ‘How does NASA's Juno mission help to understand the origin and evolution of the earth?’ (2017). Juno studies Jupiter, the oldest and largest planet, whose make-up preserves the material of the early solar nebula — so the answer needs this chapter's nebula → planetesimal → planet sequence and the earth's later evolution.
- Answer frame: origin of the universe (Big Bang, evidence) → stars and planets (nebula, planetesimals, accretion) → evolution of the earth (lithosphere, atmosphere, hydrosphere, life) → why it matters (resources, habitability, climate history).
- Use a sketch: a Big Bang cone, the three-panel planet formation, or a timeline with 4,600 / 4,000 / 3,800 / 2,000 million years — each takes under a minute and earns marks.
Self-check
Tap an option. NCERT's own exercise questions come first; the rest test the figures and common confusions.
1. Which one of the following figures represents the age of the earth?
2. Which one of the following is not related to the formation or modification of the present atmosphere?
3. Life on the earth appeared around how many years before the present?
4. A light year is a unit of…
5. According to the Big Bang theory, the universe is expanding because…
6. Which is the correct order in the formation of planets?
7. The process by which gases were outpoured from the earth's interior is called…
UPSC questions from this chapter
Open any question to attempt it in the Question bank — your attempt is saved to your progress.