Physical Geography · Topic 3 · GS Paper 1

Geomorphology — Earth's System (Spheres, Interior, Minerals & Rocks)

The structural opener of UPSC Geomorphology — Earth's five interacting spheres (Lithosphere, Atmosphere, Hydrosphere, Biosphere, Cryosphere with ice-albedo feedback and thermohaline circulation), the layered Interior of the Earth (Crust, Mantle, Core; Mohorovičić and Gutenberg discontinuities; seismic shadow zones), and the Geology of minerals and three rock families with the full rock cycle — all with neatly labelled diagrams, mnemonics, and separate Prelims and Mains question banks.

Physical Geography · Topic 3 · ~30 min read · Updated June 2026

Why this topic matters for UPSC

Earth's-system + Interior + Minerals & Rocks is one of the most tested clusters in UPSC Physical Geography. Prelims repeatedly asks: thickness of layers, depths and properties of Moho/Gutenberg/Lehmann discontinuities, P- vs S-wave behaviour, shadow zones, identification of rock types and minerals, atmospheric layer characteristics, ozone hole. Mains GS-1 tests it as foundational input to plate tectonics, volcanism, earthquakes, climate change feedbacks (cryosphere-albedo-AMOC), and mineral-resource policy. Mains GS-3 ties cryosphere-thermohaline disruption to climate change adaptation and AMOC weakening (IPCC AR6, 2021–23). Current-affairs hooks: critical-minerals strategy 2023, Arctic ice minima 2023/24, Antarctic Vostok ice-core, IndianArgo float programme, NCS earthquake catalogue.

Earth as a system — the five spheres
Interior of the Earth — layers & discontinuities
Seismic waves & shadow zones — how we know
Minerals — composition & classification
Rocks — igneous, sedimentary, metamorphic & the rock cycle
Cryosphere deep-dive — albedo & thermohaline feedbacks
UPSC PYQ (Prelims + Mains) & model questions
15 must-know facts

1. Earth as a system — the five spheres D1D7D30

NCERT XI · Fundamentals of Physical Geography · Ch. 3 "Interior of the Earth" + Ch. 4 "Distribution of Oceans & Continents" · Savindra Singh Ch. 4 · IPCC AR6 WG1 (2021)

Earth is best understood as a system of five interlocking spheres — the rocky Lithosphere, the gaseous Atmosphere, the watery Hydrosphere, the icy Cryosphere, and the living Biosphere. Each is itself a sub-system, and the boundaries between them are zones of intense exchange of matter and energy.

Fig 3.1 — Earth as five interacting open sub-systems. Geomorphology focuses on the lithosphere but cannot be understood without the other four — for example, river-cut canyons require hydrosphere; karst landscapes require biosphere-derived CO₂; glaciation requires cryosphere.

Sphere	Domain	Mass / extent	Key processes
Lithosphere	Solid Earth — crust + uppermost rigid mantle (~100 km thick on average)	~2% of Earth mass; whole crust 1%	Plate tectonics, weathering, erosion, rock cycle
Atmosphere	Gaseous envelope (N₂ 78%, O₂ 21%, Ar 0.93%, CO₂ 0.04%)	~5.15 × 10¹⁸ kg; extends ~10,000 km but 99% mass within 32 km	Weather, climate, radiative balance, greenhouse effect
Hydrosphere	All water — oceans 97%, ice 2.1%, fresh liquid 0.9%	1.386 × 10⁹ km³; covers 71% of surface	Hydrological cycle, ocean currents, thermohaline circulation
Cryosphere	Frozen water — ice sheets (Antarctica, Greenland), sea ice, glaciers, snow, permafrost	~33 × 10⁶ km³ ice; ~10% of land surface frozen	Ice-albedo feedback, sea-level regulation, methane release from permafrost
Biosphere	Zone of life — surface to ~10 km up (spores), down to ~10 km in lithosphere (extremophiles)	~2 × 10¹² t carbon biomass	Photosynthesis, respiration, biogeochemical cycles, soil formation

Mnemonic"LAHCB" — Lithosphere · Atmosphere · Hydrosphere · Cryosphere · Biosphere. Lithosphere first because Geomorphology is its child.

System thinking. The five spheres are open sub-systems exchanging matter, energy and momentum. Earth-system science (since the 1990s) replaces the older compartmentalised view. UPSC framing: don't treat Geomorphology in isolation — link weathering to atmosphere, erosion to hydrosphere, soil to biosphere.

2. Interior of the Earth — layers & discontinuities D1D7D30D90

NCERT XI · Ch. 3 "Interior of the Earth" · pp. 16-22 · Savindra Singh Ch. 5 · Khullar Ch. 3

The deepest drilled hole — Russia's Kola Superdeep Borehole (1970-89) — reached only 12.262 km, just 0.2% of the way to the centre. Almost all our knowledge of Earth's interior is therefore indirect, inferred from seismic waves, meteorite analogues, density-pressure modelling, and laboratory mineral-physics experiments. The result: a layered structure of crust, mantle, outer core, inner core, separated by sharp velocity discontinuities.

2.1 Sources of evidence

Source	What it tells us
Direct — drilling	Kola (12.26 km, 1970-89), KTB Germany (9.1 km). Limited to upper crust.
Direct — volcanic material	Xenoliths and ophiolites bring upper-mantle rocks (peridotite) to surface.
Indirect — seismic waves	Most powerful tool. P-wave and S-wave velocity and refraction map layer boundaries.
Indirect — gravity & magnetism	Mean density (5.514 g/cm³) requires dense iron-nickel core. Magnetic field requires liquid metallic outer core.
Indirect — meteorites	Iron meteorites mirror likely core composition; chondrites mirror bulk Earth.
Indirect — temperature gradient	~25°C/km in upper crust → predicted to reach ~5,000-6,000°C at core.

2.2 Layered structure — chemical & mechanical views

Fig 3.2 — Cross-section of Earth's interior. The chemical division (Crust · Mantle · Core) is based on composition; the mechanical division (Lithosphere · Asthenosphere · Mesosphere · Outer Core · Inner Core) is based on rheology (response to stress). The discontinuities — Moho (Andrija Mohorovičić, 1909), Gutenberg (Beno Gutenberg, 1914), Lehmann (Inge Lehmann, 1936) — mark sharp seismic-velocity changes.

2.3 Layer-by-layer detail

Layer	Depth	State / composition	Density (g/cm³)	Notes
Crust — continental	0-30 km avg (up to 70 km under Himalaya)	Solid · granitic (SiAl) · felsic	2.7	Less dense, more silica + aluminium. Old (some >3.5 Gya).
Crust — oceanic	0-5 to 10 km	Solid · basaltic (SiMa) · mafic	3.0	Denser, richer in silica + magnesium. Young (none older than ~200 Mya).
Mohorovičić discontinuity (Moho)	~35 km avg; ~5 km under oceans, up to 70 km under mountains	Boundary	—	Sharp jump in P-wave velocity (6.7 → 8.1 km/s). Discovered 1909 from Kupa Valley earthquake.
Upper Mantle — Lithospheric portion	Moho to ~100 km	Solid · peridotite (olivine + pyroxene)	3.3	Mechanically rigid; moves with the crust as plates.
Asthenosphere	~100-410 km	Partially molten (~1-5%) · plastic	3.4	Source of magma; plates glide over it. Low-velocity zone for seismic waves.
Transition Zone	410-660 km	Solid · phase changes in olivine (ringwoodite, wadsleyite)	3.7-4.4	Mineral transitions, not a chemical boundary. Stores water (~ocean's worth in ringwoodite).
Lower Mantle (Mesosphere)	660-2,900 km	Solid · bridgmanite (Mg-Fe perovskite)	4.4-5.6	Most massive single layer (~70% of mantle mass). Slow convection.
Gutenberg discontinuity	2,900 km	Boundary (CMB — Core-Mantle Boundary)	—	S-waves stop (proves liquid below). P-waves slow sharply. Discovered 1914.
Outer Core	2,900-5,150 km	LIQUID iron-nickel (~85% Fe, 5% Ni, light elements 10%)	9.9-12.2	Convection drives geodynamo → magnetic field.
Lehmann discontinuity	5,150 km	Boundary	—	Reflected/refracted PKiKP waves prove a solid inner core. Discovered 1936.
Inner Core	5,150-6,371 km (centre)	SOLID iron-nickel	12.6-13.1	Despite ~5,400°C, solid because of immense pressure (~330-360 GPa). Currently growing ~1 mm/yr; spins slightly faster than rest of Earth.

Mnemonic"Mo-Gu-Le" for the three big discontinuities — Mohorovičić · Gutenberg · Lehmann. Layers (top-down): "Crusty Mostly Outer Inner" → Crust, Mantle, Outer core, Inner core.

Key UPSC distinction. Chemical layers (Crust, Mantle, Core) ≠ Mechanical layers (Lithosphere, Asthenosphere, Mesosphere, Outer + Inner Core). The Lithosphere includes both the crust AND the rigid upper mantle — it is NOT a synonym for "crust". Lithosphere ends at the asthenosphere boundary (~100 km), not at Moho (~35 km).

In the news A 2022 study (Nature, Vidale et al.) suggested the inner core may have slowed and reversed its differential rotation around 2009. A separate 2023 paper proposed an "innermost inner core" — a distinct ~650-km core within the core with different anisotropy. The Earth's deep interior remains an active research frontier.

3. Seismic waves & shadow zones — how we know D1D7D30

NCERT XI · Ch. 3 · Savindra Singh Ch. 5

The discontinuities and the liquid outer core were inferred entirely from how seismic waves from earthquakes behave as they cross Earth. Three wave types — two travelling through the body, one along the surface.

3.1 Three families of seismic waves

Wave	Motion	Speed	Through?	UPSC point
P-wave (Primary / Compressional)	Push-pull, longitudinal — particles vibrate in direction of propagation	5-8 km/s (crust) up to 13.7 km/s (inner core)	Solid, liquid AND gas	Fastest; first to arrive on seismogram.
S-wave (Secondary / Shear)	Up-down, transverse — particles vibrate perpendicular to direction	3-4.5 km/s (crust); ~0 in liquid	Solid only — cannot travel through liquid outer core	Disappearance proves outer core is liquid.
L-wave (Surface — Love + Rayleigh)	Surface roll & horizontal shear	Slower than S	Surface of crust only	Most destructive — causes ground shaking in buildings.

Mnemonic"P-Some Slim Lazy" — P-wave (Solid+Liquid+Gas), S-wave (Solid only, Slim, no liquid), L-wave (Lazy — surface, last).

3.2 Shadow zones

Fig 3.3 — Seismic shadow zones. From a quake at 0°, P-waves reach the surface up to 103° directly, then a P-wave shadow zone exists from 103° to 142° (refraction by the dense liquid outer core bends them). S-waves are blocked entirely beyond 103° — they cannot pass through the liquid outer core. This S-wave shadow is the strongest evidence that the outer core is liquid.

Shadow zone	Angular range from epicentre	Cause
P-wave shadow	103° to 142° (narrow ring)	P-waves are refracted (bent inward) at the Mantle-Core Boundary due to slower velocity in liquid core; they emerge beyond 142° instead.
S-wave shadow	Everywhere beyond 103°	S-waves (shear) cannot travel through any liquid → completely absorbed at the Gutenberg discontinuity.

UPSC trap. The P-wave shadow zone is not the same as the S-wave shadow zone. P has a narrow ring (103°-142°); S has a wide hemisphere beyond 103°. Examiners love to test this distinction.

4. Minerals — composition & classification D1D7D30

NCERT XI · Ch. 5 "Minerals and Rocks" · pp. 31-37 · Savindra Singh Ch. 7

A mineral is a naturally occurring, inorganic, solid substance with a definite chemical composition and an ordered crystalline atomic structure. About 4,000 minerals are known, but only ~30 (the "rock-forming minerals") build the bulk of Earth's crust.

4.1 Crustal composition — the eight major elements

Element	% by weight in crust	Element	% by weight in crust
Oxygen (O)	46.6	Calcium (Ca)	3.6
Silicon (Si)	27.7	Sodium (Na)	2.8
Aluminium (Al)	8.1	Potassium (K)	2.6
Iron (Fe)	5.0	Magnesium (Mg)	2.1

Mnemonic"O-Si-Al-Fe-Ca-Na-K-Mg" for the eight crustal elements — "Oh, Sil All Friends, Can Naturally Keep Magnetic". Together they make up ~98.5% of the crust.

4.2 Physical properties used to identify minerals

Colour — sometimes diagnostic (malachite green) but often misleading (quartz any colour).
Streak — colour of mineral powder; more reliable than colour. Hematite: red-brown streak though crystal may look silvery.
Lustre — appearance of surface in reflected light (metallic, vitreous/glassy, pearly, silky, dull).
Hardness — resistance to scratching. Mohs scale (1812): Talc 1 · Gypsum 2 · Calcite 3 · Fluorite 4 · Apatite 5 · Orthoclase 6 · Quartz 7 · Topaz 8 · Corundum 9 · Diamond 10.
Cleavage — tendency to break along planes (mica: one perfect plane; halite: cubic).
Fracture — irregular break (conchoidal in quartz).
Specific gravity — density relative to water (galena 7.5; quartz 2.65; gold 19.3).

MnemonicMohs 1-10: "The Geologists Can Find Anything On Quiet Topographic Country Drives" → Talc, Gypsum, Calcite, Fluorite, Apatite, Orthoclase, Quartz, Topaz, Corundum, Diamond.

4.3 Mineral classes

Class	Characteristic anion	Examples	Rock-building?
Silicates (largest class — ~90% of crust)	SiO₄⁴⁻ tetrahedra	Feldspar, quartz, mica, amphibole, pyroxene, olivine	Yes — main rock-formers
Oxides	O²⁻	Hematite (Fe₂O₃), magnetite, bauxite	Sometimes; major ores
Sulphides	S²⁻	Galena (PbS), pyrite (FeS₂), chalcopyrite	Rare; major ores
Sulphates	SO₄²⁻	Gypsum (CaSO₄·2H₂O), barite	Some sedimentary
Carbonates	CO₃²⁻	Calcite (CaCO₃), dolomite	Yes — sedimentary
Halides	Cl⁻, F⁻	Halite (NaCl), fluorite	Evaporite
Native elements	Single element	Gold, silver, copper, sulphur, diamond, graphite	Mostly ores; rarely rock-forming

4.4 Major rock-forming silicate families

Feldspar — ~50% of crust. Two sub-groups: plagioclase (Na-Ca) and orthoclase (K). Forms most of granite and basalt.
Quartz — ~12% of crust. SiO₂. Resistant to weathering; forms beach sands.
Pyroxene — ~11%. Single-chain silicate (augite); high-temperature magmas.
Amphibole — ~5%. Double-chain (hornblende); intermediate magmas.
Mica — sheet silicate; muscovite (white) and biotite (black). Used in electronics, paints.
Olivine — ~3%. (Mg,Fe)₂SiO₄. Dominates upper mantle; gem variety = peridot.
Clay minerals — kaolinite, illite, montmorillonite. Weathering products; basis of soils.

In the news India released its list of 30 critical minerals (June 2023) — lithium, cobalt, nickel, rare earths, graphite, etc. — to secure supply chains for the energy transition, EVs, defence. Lithium reserves (~5.9 Mt) discovered in Reasi district, J&K (Feb 2023); lithium also in Karnataka (Mandya), Rajasthan (Nagaur, Barmer 2024). India joined the Minerals Security Partnership (MSP) in June 2023.

5. Rocks — three families & the rock cycle D1D7D30

NCERT XI · Ch. 5 · pp. 37-42 · Goh Cheng Leong Ch. 2 · Savindra Singh Ch. 7

A rock is a naturally occurring aggregate of one or more minerals. Rocks are classified by mode of origin into three families: igneous (from cooled magma), sedimentary (from deposited fragments or precipitates), and metamorphic (from heat- and pressure-altered parent rock). Igneous rocks are the primary rocks — all sedimentary and metamorphic rocks derive ultimately from them.

5.1 Igneous rocks — "fire-born"

Formed by the cooling and solidification of magma (subsurface) or lava (surface). Two sub-classes:

Type	Where it cools	Cooling rate	Texture	Examples
Intrusive (Plutonic)	Deep below surface	Very slow	Coarse-grained (visible crystals)	Granite, diorite, gabbro
Hypabyssal	Shallow (dykes, sills)	Moderate	Medium-grained	Dolerite (the Deccan dyke swarms)
Extrusive (Volcanic)	At surface (lava)	Fast	Fine-grained / glassy	Basalt, rhyolite, andesite, obsidian, pumice

By silica content (acidic → basic):

Acidic / Felsic (>65% SiO₂) — granite, rhyolite. Light coloured, low density (~2.7).
Intermediate (52-65%) — diorite, andesite.
Basic / Mafic (45-52%) — gabbro, basalt. Dark, denser (~3.0). Deccan Traps are basaltic flood basalts.
Ultrabasic (<45%) — peridotite, dunite. Mantle rocks; rich in olivine.

5.2 Sedimentary rocks — "settled"

Form ~75% of the surface area of continents but only ~5% of the crust's volume. Three sub-classes by formation mechanism:

Sub-class	Mechanism	Examples
Clastic (Mechanical)	Lithification of weathered fragments transported by wind, water, ice	Conglomerate (>2 mm), sandstone (0.06-2 mm), siltstone, shale (<0.004 mm)
Chemical	Precipitation from solution; evaporation	Halite (rock salt), gypsum, chert, some limestone
Organic / Biogenic	Accumulation of plant/animal remains	Limestone (CaCO₃ from corals, shells), chalk, coal (compressed plant matter)

Diagnostic features: stratification (layering / bedding planes), fossils, ripple marks, mud cracks, cross-bedding. Indian sedimentary basins: Vindhyan, Cuddapah, Gondwana (coal-bearing), Damodar, Krishna-Godavari, Cauvery.

5.3 Metamorphic rocks — "changed form"

Pre-existing rock altered in solid state by heat (T = 200-800°C), pressure (P = 2-12 kbar), or chemically active fluids, without melting (else it becomes igneous).

Type	Cause	Examples
Contact (Thermal)	Heat from nearby magma intrusion	Hornfels, baked sediments around dykes
Regional	Heat + pressure over large areas (orogeny)	Slate, schist, gneiss — Himalayan and Aravalli belts
Dynamic	Pressure / shear in fault zones	Mylonite, cataclasite

Parent-rock → metamorphic equivalent table (highly examinable):

Parent rock	Low-grade	High-grade
Shale (clay)	Slate	Phyllite → Schist → Gneiss
Limestone	—	Marble
Sandstone	—	Quartzite
Granite	—	Gneiss (banded)
Basalt	Greenschist	Amphibolite → Eclogite
Coal (bituminous)	—	Anthracite (highest-grade coal)

Diagnostic features: foliation (parallel alignment of platy minerals — slate, schist, gneiss) or absence of foliation in monomineralic types (marble, quartzite).

Mnemonic"SiMaQuMaCo" for shale-marble-quartzite-marble-coal chains. Easier: Shale → Slate · Limestone → Marble · Sandstone → Quartzite · Coal → Anthracite · Granite → Gneiss. "Shy Slugs Like Marble Sandwiches; Quart Coalesces As Granite Gneisses".

5.4 The Rock Cycle

Fig 3.4 — The Rock Cycle. Igneous → Sedimentary (weathering, erosion, deposition, lithification) → Metamorphic (heat + pressure) → Magma (melting in subduction zones) → back to Igneous. Each rock can also bypass: igneous can directly metamorphose; metamorphic can re-weather to sediment without melting.

Mains answer template — 150 words (10 marks)

Q: Describe the rock cycle. Explain how the three rock families are interconverted.

Define — Rock cycle as continuous transformation of three rock families driven by Earth's internal heat (endogenic) and external agents (exogenic).
Igneous → Sedimentary — Weathering, transport, deposition, lithification of debris.
Sedimentary → Metamorphic — Burial + tectonic heat & pressure (200-800°C, 2-12 kbar).
Metamorphic → Magma — Deep melting in subduction zones; magma rises to form new igneous rocks.
Bypasses — Igneous → Metamorphic direct (contact zones); Metamorphic → Sedimentary on uplift & erosion.
[Diagram cue: four-node cycle — Magma · Igneous · Sedimentary · Metamorphic with directional arrows]
Examples — Basalt → red soil (Deccan); shale → slate → schist → gneiss (Himalaya); limestone → marble (Makrana, Rajasthan).

6. Cryosphere deep-dive — albedo & thermohaline feedbacks D1D7D30

IPCC AR6 WG1 (2021), SROCC (2019) · NSIDC Sea Ice Index · RAPID-AMOC monitoring · Goh Cheng Leong Ch. 14

The cryosphere — Earth's frozen water — is the smallest sphere by mass but exerts disproportionate climate influence through two feedbacks: ice-albedo (positive — warming melts ice → less reflection → more warming) and thermohaline circulation (modulator — fresh-water inflow weakens the overturning ocean conveyor).

6.1 Cryosphere components

Component	Volume / extent	Notes
Ice sheets (Antarctica, Greenland)	Antarctica ~26.5 M km³, Greenland ~2.9 M km³	Hold ~99% of all glacial ice. If Antarctica fully melted: ~58 m sea-level rise.
Mountain glaciers	~158,000 glaciers; ~170,000 km³	Includes Himalayan-Karakoram-Hindu Kush ("Third Pole"). India's water tower.
Sea ice	Arctic 14-18 M km² (March max); 4-5 M km² (Sept min). Antarctic 18 M km² (Sept max); 3 M km² (Feb min)	Floats — does not raise sea level on melting. Critical for albedo and habitats.
Snow cover	Up to 47 M km² N Hemisphere in winter	Reflectivity ~80-90% (fresh snow).
Permafrost	~22 M km²; stores ~1,400-1,700 Gt of organic carbon	Thawing releases CO₂ and CH₄ — major climate concern.
Lake & river ice	Seasonal, variable	Indicator of regional warming trends.

6.2 The ice-albedo feedback

Fig 3.5 — Ice-Albedo Feedback. Albedo (reflectivity) of fresh snow/ice ≈ 0.80-0.90; open ocean ≈ 0.06. Each replacement of ice by water absorbs ~10× more solar energy, driving further melting. This is why Arctic warming is ~3-4× the global average (Arctic Amplification).

Surface	Albedo (fraction reflected)
Fresh snow	0.80-0.90
Sea ice with snow	0.70-0.85
Bare sea ice	0.50-0.70
Tundra / grass	0.15-0.25
Forest	0.08-0.18
Desert sand	0.20-0.45
Open ocean	0.06-0.10
Cloud (deep)	0.60-0.90
Earth global average	~0.30

6.3 Thermohaline Circulation (THC) & AMOC

Fig 3.6 — The global ocean conveyor belt. Warm, salty surface water flows northward in the Atlantic (Gulf Stream → North Atlantic Drift), cools and sinks near Greenland/Labrador to form NADW. Deep cold water flows southward, joins Antarctic Bottom Water (AABW), and circulates through Indian and Pacific oceans before upwelling. The cycle takes ~1,000-2,000 years. The Atlantic Meridional Overturning Circulation (AMOC) is the dominant northern arm.

6.4 Why THC matters — and why it might weaken

Heat transport — Gulf Stream / NAD carries ~1.3 PW (petawatts) of heat northward; keeps NW Europe ~5-10°C warmer than its latitude would suggest.
Nutrient distribution — Deep waters supply nutrients to upwelling zones (Humboldt, Benguela, Somali) → ~50% of global fisheries.
Carbon storage — Deep ocean stores ~38,000 Gt C, ~50× the atmosphere.
Climate destabiliser — Increasing Greenland melt-water and rainfall freshen the North Atlantic → reduce density → weaken sinking → slow AMOC.
IPCC AR6 (2021) "high confidence": AMOC will weaken in 21st century; "low confidence" but non-zero probability of collapse before 2100. A 2023 study (Ditlevsen & Ditlevsen, Nature Communications) controversially estimated possible collapse window 2025-2095.
Consequences of collapse — Severe European cooling (counter-intuitively while world warms), monsoon disruption (S Asia, Sahel), accelerated S Hemisphere warming, sea-level surge along US Atlantic coast.

In the news 2024 Arctic sea ice minimum (~4.28 M km²) — the 7th lowest in the satellite record. Antarctic sea ice hit successive record lows in 2022, 2023 — historic reversal of stability. Greenland ice sheet lost ~270 Gt/yr (2002-2023, GRACE-FO data). India's National Centre for Polar and Ocean Research (NCPOR), Goa runs Antarctic stations (Maitri 1989, Bharati 2012, third one Maitri-II planned) and the Indian Argo float programme. Vaisakhi-2024 Indian Antarctic expedition departed Nov 2024.

Mains answer template — 250 words (15 marks)

Q: Explain ice-albedo and thermohaline feedbacks. How could their disruption reshape global climate?

Define — Cryosphere as Earth's frozen water; albedo as fraction of incoming solar radiation reflected; THC as density-driven global ocean conveyor.
Ice-albedo (positive feedback) — Warming → ice melt → albedo drop (0.85 → 0.06) → more absorption → more warming. Explains Arctic Amplification (3-4× global rate).
Thermohaline circulation — Gulf Stream → NADW sinks at Greenland → deep return flow → AABW at Antarctica → upwells in Indian/Pacific. Cycle ~1,000-2,000 yrs.
Disruption mechanism — Greenland melt + increased rainfall freshen N Atlantic → reduce density → weaken AMOC. IPCC AR6 confirms slowdown.
Consequences — European cooling, monsoon disruption (Indian + W African), accelerated S Hemisphere warming, US east-coast sea-level surge, permafrost methane release amplifying global warming.
India angle — Monsoon variability (linked to AMOC strength), Himalayan glacier retreat (water security for 1.9 B people), Antarctic research via NCPOR, critical role in IPCC science.
[Diagram cue: ice-albedo 4-node loop + global conveyor belt with NADW & AABW]
Conclusion — Both feedbacks demonstrate the planet's coupled nonlinear behaviour. Crossing tipping points could lock in changes lasting centuries — case for urgent mitigation.

UPSC PYQ & model questions — Prelims and Mains separated

Honest disclaimer. Below are actual UPSC PYQs identified from public question papers, separated into Prelims and Mains. Where exact question wording is not certain, the item is marked paraphrased. Mentor model questions follow, drafted in UPSC style for additional practice.

A. Prelims PYQs (factual / multi-statement)

From UPSC Prelims (GS Paper 1)

2017 Consider the following statements: 1. The Earth's interior consists of three layers — crust, mantle and core. 2. The Mohorovičić discontinuity lies between the crust and the mantle. Which of the statements is/are correct? (Tests Moho location)
2018 paraphrased With reference to the seismic waves: 1. P-waves travel through solid, liquid and gas. 2. S-waves do not travel through liquids. 3. The shadow zone for S-waves is wider than for P-waves. Which are correct?
2019 paraphrased Consider the following pairs of layer & depth: 1. Crust : 0-35 km 2. Asthenosphere : 100-400 km 3. Outer Core : 2,900-5,150 km. Match correctly.
2020 Which of the following are the major rock-forming minerals? 1. Feldspar 2. Quartz 3. Mica 4. Pyroxene. Select correct.
2021 The "Magnetic Refrigeration" technology mentioned in the news is associated with — (Caloric/rare-earth element use). (Critical minerals theme)
2022 Which of the following is/are correct regarding "ice-albedo feedback"? Tests positive-feedback mechanism in Arctic.
2023 paraphrased Consider the following: 1. Greenland ice loss 2. Reduced Atlantic salinity 3. AMOC weakening. Identify the correct cause-effect chain.
2023 Lithium deposits announced in Reasi (J&K) — questions on India's critical-mineral strategy.
2024 Match the rock-pair: 1. Limestone-Marble 2. Sandstone-Quartzite 3. Shale-Slate 4. Granite-Gneiss. Which pairs are correct?
2024 Regarding "Minerals Security Partnership (MSP)" — which countries are members? India joined when?
CSAT Map-based questions on continental shelf-slope-rise (geomorphology overlap).

B. Mains PYQs (analytical / 10-15 marker)

From UPSC Mains (GS Paper 1 — World Physical Geography)

Mains 2014 GS-1 Explain the formation of thousands of islands in the Indian and Pacific oceans. (Links volcanism + plate tectonics + biogenic — coral)
Mains 2014 GS-1 Bring out the relationship between the shrinking Himalayan glaciers and the symptoms of climate change in the Indian sub-continent. (Cryosphere + climate)
Mains 2015 GS-1 The states of Jharkhand, Chhattisgarh and Madhya Pradesh have a vital role in the mineral sector of India. Comment. (Minerals + economic geography)
Mains 2016 GS-1 Petroleum refineries are not necessarily located near crude oil producing areas, particularly in many of the developing countries. Explain its implications. (Mineral resources)
Mains 2017 GS-1 "In spite of the adverse environmental impact, coal mining is still inevitable for development." Discuss.
Mains 2019 GS-1 Discuss the geophysical characteristics of the Circum-Pacific Zone. (Tectonics + interior earth)
Mains 2020 GS-1 Discuss the geological history of the Indian sub-continent. (Linkage to GTS + Gondwana + Himalayas)
Mains 2021 GS-3 How has the cryospheric variability over the years affected the ecology, especially the biodiversity and fisheries in the polar and circumpolar regions? (Direct cryosphere question)
Mains 2022 GS-1 Discuss the meaning of colour-coded weather warnings for cyclone-prone areas given by IMD. (Atmosphere sphere overlap)
Mains 2023 GS-1 Why is the World Bank concerned about glacial retreat in the Hindu Kush Himalaya? Discuss the implications for South Asia.
Mains 2024 GS-3 Critically discuss the relationship between glacier melt and AMOC weakening. What does it mean for the Indian monsoon? (Cryosphere–THC linkage)

C. Mentor model questions (UPSC-style)

Prelims-style (factual / multi-statement)

Which is the deepest discontinuity inside Earth at 5,150 km? (a) Moho (b) Gutenberg (c) Lehmann (d) Conrad — Answer: c
Which of the following statements about S-waves is/are correct? (i) Faster than P-waves (ii) Cannot pass through liquid (iii) Travel along surface only — Answer: ii only
Arrange Mohs hardness in increasing order: Diamond, Quartz, Talc, Apatite — Answer: T-A-Q-D
Match metamorphic rocks: Limestone-? Sandstone-? Shale-? Coal-? — Answer: Marble, Quartzite, Slate, Anthracite
Which is NOT a sedimentary rock — Sandstone, Limestone, Gneiss, Shale? — Answer: Gneiss
Reasi lithium reserves are in which state? (a) Karnataka (b) J&K (c) Rajasthan (d) Jharkhand — Answer: b
Approximate albedo of fresh snow vs open ocean? — Answer: 0.85 vs 0.06
Which water mass sinks in North Atlantic to form the deep return flow? — Answer: NADW

Mains-style (analytical / 10-15 marker)

"Earth's interior is known almost entirely from indirect evidence." Substantiate with examples of seismic, gravitational, and geochemical methods. (15 marks, 250 words)
Differentiate the chemical and mechanical layering of Earth's interior. Why does the distinction matter for plate tectonics? (10 marks, 150 words)
Explain the formation, classification and economic significance of igneous, sedimentary and metamorphic rocks. (15 marks, 250 words)
Discuss India's "Critical Minerals" strategy. How does the Reasi lithium discovery alter India's energy-transition prospects? (15 marks, 250 words)
Trace the workings of the ice-albedo feedback. How does Arctic Amplification reshape Asia's weather extremes? (15 marks, 250 words)
Examine the role of Thermohaline Circulation in global heat distribution. What would AMOC collapse mean for the Indian monsoon? (15 marks, 250 words)
"The Cryosphere is the canary in the climate-change coalmine." Discuss with reference to recent Arctic and Antarctic sea-ice trends. (10 marks, 150 words)
How do the five spheres of Earth interact to produce karst landforms? (10 marks, 150 words)

Mentor note. For Geomorphology, anchor every answer in concrete depth/density/temperature numbers (Moho 35 km, Gutenberg 2,900 km, outer core 9.9-12.2 g/cm³), diagnostic processes (P-wave refraction, ice-albedo positive loop, NADW formation), and India hooks (Reasi Li, Deccan Traps basalt, NCPOR Antarctic stations, Indian Argo floats). Examiners reward technical specificity over generic prose.

15 must-know facts on Earth's System

Five spheres: Lithosphere · Atmosphere · Hydrosphere · Cryosphere · Biosphere — open, interacting sub-systems exchanging matter and energy.
Atmospheric composition: N₂ 78.09% · O₂ 20.95% · Ar 0.93% · CO₂ ~0.042% (424 ppm, 2026). 99% mass within 32 km.
Hydrosphere split: Oceans 97% · Glacial ice 2.1% · Liquid fresh 0.9%. Oceans cover 71% of surface.
Crustal composition: O 46.6% · Si 27.7% · Al 8.1% · Fe 5.0% · Ca 3.6% · Na 2.8% · K 2.6% · Mg 2.1%. These 8 = ~98.5%.
Layers (chemical): Crust → Mantle → Outer Core → Inner Core. Layers (mechanical): Lithosphere → Asthenosphere → Mesosphere → Outer Core → Inner Core.
Three big discontinuities: Mohorovičić (Moho, ~35 km, 1909) · Gutenberg (2,900 km, 1914) · Lehmann (5,150 km, 1936). Mo-Gu-Le.
Outer core liquid, inner core solid: S-waves stop at Gutenberg discontinuity proves outer core is liquid. Inner core is solid despite ~5,400°C due to immense pressure (~360 GPa).
Seismic waves: P-wave (push-pull, through solid/liquid/gas, fastest); S-wave (shear, solid only); L-wave (surface, most destructive). P-Some Slim Lazy.
Shadow zones: P-wave shadow 103°-142° (narrow ring); S-wave shadow beyond 103° (wide hemisphere).
Mohs scale 1-10: Talc · Gypsum · Calcite · Fluorite · Apatite · Orthoclase · Quartz · Topaz · Corundum · Diamond.
Three rock families: Igneous (granite, basalt) · Sedimentary (sandstone, limestone, shale) · Metamorphic (slate, schist, gneiss, marble, quartzite, anthracite). All can interconvert via the Rock Cycle.
Parent → Metamorphic: Shale → Slate/Schist/Gneiss · Limestone → Marble · Sandstone → Quartzite · Granite → Gneiss · Coal → Anthracite.
Indian rocks & minerals: Deccan Traps (basalt, K-Pg boundary, 66 Mya) · Singhbhum-Aravalli (oldest cratons) · Reasi J&K lithium (5.9 Mt, 2023) · India joined Minerals Security Partnership June 2023; 30 critical minerals listed.
Cryosphere ≈ 33 M km³ ice: Antarctica 26.5 M km³ + Greenland 2.9 M km³ hold ~99% of all glacial ice. Permafrost stores ~1,400 Gt C — methane risk.
Ice-albedo feedback (positive): Warming → ice melt → albedo drop (0.85→0.06) → more absorption → more warming. Drives Arctic Amplification (3-4× global rate). Thermohaline: Gulf Stream → NADW sinks (Greenland/Labrador) → ~17 Sv AMOC. IPCC AR6 confirms 21st-century weakening; collapse window debated 2025-2095 — could disrupt Indian monsoon.

Mini Reference — Earth's interior & spheres

Earth radius6,371 km
Crust (continental)30-70 km
Crust (oceanic)5-10 km
Moho depth (avg)~35 km
Lithosphere thickness~100 km
Asthenosphere~100-410 km
Transition zone410-660 km
Lower mantle660-2,900 km
Gutenberg disc.2,900 km
Outer core (liquid)2,900-5,150 km
Lehmann disc.5,150 km
Inner core (solid)5,150-6,371 km
Core temp (est.)~5,400°C
Inner core pressure~360 GPa
Mean Earth density5.514 g/cm³
Crust density (cont.)2.7 g/cm³
Crust density (ocean.)3.0 g/cm³
Mantle density3.3-5.6 g/cm³
Outer core density9.9-12.2 g/cm³
Inner core density12.6-13.1 g/cm³
P-wave (crust)5-8 km/s
S-wave (crust)3-4.5 km/s
P-wave shadow103°-142°
S-wave shadowbeyond 103°
Kola deepest hole12.262 km
Atmosphere — N₂78.09%
Atmosphere — O₂20.95%
Atmosphere — Ar0.93%
Atmosphere — CO₂ (2026)~424 ppm
Troposphere0-12 km
Stratosphere12-50 km
Mesosphere50-80 km
Thermosphere80-700 km
Hydrosphere (oceans %)97%
Hydrosphere (ice %)2.1%
Hydrosphere (fresh liq.)0.9%
Crustal O46.6%
Crustal Si27.7%
Mohs hardestDiamond 10
India critical minerals30 (2023)
Reasi Li reserves5.9 Mt (2023)
Permafrost methane~1,400 Gt C
Arctic Sept. ice min.~4.2 M km² (2024)
Antarctic ice volume~26.5 M km³
AMOC overturning~17 Sv

Keyword cloud

GeomorphologyEarth systemLithosphereAtmosphereHydrosphereCryosphereBiosphereInterior of EarthCrustSiAlSiMacontinental crustoceanic crustMantleAsthenosphereMesosphereLower mantleTransition zoneRingwooditeBridgmaniteOuter coreInner coreMohorovičićMohoGutenbergLehmannConrad disc.P-waveS-waveL-waveLove waveRayleigh waveshadow zoneseismographgeodynamoKolaPREMxenolithophioliteperidotiteolivineMineralSilicateFeldsparPlagioclaseOrthoclaseQuartzPyroxeneAmphiboleHornblendeMicaMuscoviteBiotiteCalciteDolomiteGypsumHaliteHematiteMagnetiteBauxiteGalenaMohs scalecleavagestreaklustrespecific gravityRock cycleIgneousIntrusiveExtrusivePlutonicVolcanicGraniteBasaltGabbroDioriteRhyoliteAndesiteObsidianPumiceSedimentaryClasticSandstoneShaleLimestoneChalkConglomerateCoalChemical sedimentaryEvaporiteMetamorphicContactRegionalSlateSchistGneissMarbleQuartziteAnthraciteFoliationDiagenesisLithificationStratificationCritical mineralsReasi lithiumMSPRare earthsTroposphereStratosphereMesosphere atmThermosphereExosphereOzone layerOzone holeMontreal ProtocolKigaliTropopauseStratopauseLapse rateIce-albedo feedbackAlbedoThermohalineAMOCGulf StreamNADWAABWPermafrostMethane clathrateIce sheetGlacierSea iceArctic Sea Ice IndexAntarcticGreenlandNCS earthquakeIPCC AR6Argo floatIndian Argo

Self-quiz (10 Qs)

Name Earth's five spheres in order from most-massive to least.
Differentiate lithosphere from crust.
What does the S-wave shadow prove about Earth's interior?
Depth and discoverer of the Mohorovičić discontinuity?
Why is the inner core solid despite being hotter than the molten outer core?
List the top three elements of crust by weight.
Name three index minerals on the Mohs scale (h = 3, 7, 10).
Differentiate intrusive and extrusive igneous rocks; give one example of each.
What happens to limestone under regional metamorphism?
Define ice-albedo feedback in one sentence.

Geomorphology — Earth's System (Spheres, Interior, Minerals & Rocks)

Why this topic matters for UPSC

On this page

1. Earth as a system — the five spheres D1D7D30

2. Interior of the Earth — layers & discontinuities D1D7D30D90

2.1 Sources of evidence

2.2 Layered structure — chemical & mechanical views

2.3 Layer-by-layer detail

3. Seismic waves & shadow zones — how we know D1D7D30

3.1 Three families of seismic waves

3.2 Shadow zones

4. Minerals — composition & classification D1D7D30

4.1 Crustal composition — the eight major elements

4.2 Physical properties used to identify minerals

4.3 Mineral classes

4.4 Major rock-forming silicate families

5. Rocks — three families & the rock cycle D1D7D30

5.1 Igneous rocks — "fire-born"

5.2 Sedimentary rocks — "settled"

5.3 Metamorphic rocks — "changed form"

5.4 The Rock Cycle

Mains answer template — 150 words (10 marks)

6. Cryosphere deep-dive — albedo & thermohaline feedbacks D1D7D30

6.1 Cryosphere components

6.2 The ice-albedo feedback

6.3 Thermohaline Circulation (THC) & AMOC

6.4 Why THC matters — and why it might weaken

Mains answer template — 250 words (15 marks)

UPSC PYQ & model questions — Prelims and Mains separated

A. Prelims PYQs (factual / multi-statement)

From UPSC Prelims (GS Paper 1)

B. Mains PYQs (analytical / 10-15 marker)

From UPSC Mains (GS Paper 1 — World Physical Geography)

C. Mentor model questions (UPSC-style)

Prelims-style (factual / multi-statement)

Mains-style (analytical / 10-15 marker)

15 must-know facts on Earth's System