Everyday Science — Chapter 2

Earth & Its Spheres — the Lithosphere, the Hydrosphere, the Atmosphere and the Ozone Layer

Why this chapter matters: the Earth is not one thing in the papers — it is three spheres, and PPSC builds most of its Everyday Science MCQs from them. Our verified banks hold 44 questions matching this topic by question text, and the weight sits where this chapter puts it: the lithosphere and the Earth’s interior (15 questions) — the crust’s oxygen, the Moho, the rock types — followed by the atmosphere and its layers (12), the hydrosphere and the water cycle (9) and ozone (8). The lectures teach the whole topic at full depth (EDS Lecture 2 for the spheres, EDS Lecture 1 Section 11 for the Earth’s interior), and the IBES Everyday Science capsule bank sits behind it. Learn the layer table in Section 4 and the rock table in Section 2 and the chapter answers itself. The food-science half of EDS Lecture 2 — balanced diet, vitamins, proteins — is not taught here: it belongs to Chapter 5 (Vitamins, Food & Nutrition), and is cross-linked from there, not double-taught.

1. The framework — biotic, abiotic, and the three spheres

• Biotic = living — animals (including us), plants, microorganisms/microbes.
• Abiotic = non-living. The trick is the prefix: “a-” makes a word its opposite (like ahimsa = non-violence).
• The abiotic surroundings are three spheres, and the names give the subject away:
  • Lithosphere — litho = rocks/land.
  • Hydrosphere — hydro = water.
  • Atmosphere — air.
• Renewable resources are reusable after use: land, water.
• Non-renewable resources are one-time use: petroleum, coal. Asked directly: petroleum is a non-renewable resource — once it is in the car tank, it is gone.

2. The lithosphere — the Earth’s interior and its rocks

The Earth’s interior — three layers, inside out

Crust → Mantle → Core (this is the Earth-structure section carried over from Chapter 1, taught here in full).

• The crust comes in two kinds: oceanic crust (under the sea) and continental crust (the land).
• Bank facts that hang on this table: the boundary layer that separates the Earth’s crust from the mantle is the Moho (the Mohorovičić discontinuity); the most common elements in the Earth’s crust are silicon, aluminium and oxygen; silicon is 27.72% of the crust; the second most abundant metal in the crust is iron; and the science of the chemical composition of the Earth’s crust and its changes is geochemistry.
• The crust’s oxygen is the same oxygen the banks ask about in the “element without which earth life cannot survive beyond a few minutes” question — it forms about half of the Earth’s crust and over one-fifth of the air we breathe.

Rocks — the three types

• Rock cycle: Igneous → (weathering) → Sedimentary → (heat + pressure) → Metamorphic → can become igneous or sedimentary again.
• A crack in the Earth’s crust through which hot magma and gases force out is a volcano — the banks ask it in exactly those words.

3. The hydrosphere — water, and the cycle that moves it

• Earth’s surface: 71% water, 29% land. Option strategy from the lecture: if 71 is there, tick it; else the 70.9/70.8/70.7 variants; only then 70.
• Of all water: 97% saline (the 5 big oceans: Pacific, Atlantic, Southern, Indian, Arctic), 3% fresh — the only drinkable water, in lakes, rivers, ponds and glaciers.
• Of that 3%, only about 1% is readily usable — most of the rest is locked in glaciers. This is the water running the renewable cycle below.
• Freshwater split (PMS Screening 2026 Tough GK Mock, Q24; mock-only bank row, no mark claimed): of all freshwater, about 68.7% is locked in ice caps and glaciers, about 30.1% is groundwater, and only about 1.2% is surface and other water (lakes, rivers, soil moisture, atmosphere). So the biggest source of freshwater on Earth is glaciers and ice caps — and, of the freshwater that is not ice, the largest share is groundwater.
• Bank facts that hang on this section: sea water is saline because rivers carry soluble minerals from the mountains; the most abundant elements in sea water are sodium and chlorine, and the most common salt in seawater is sodium chloride; the purest form of water comes from rain (heavy rains / rain water — asked both ways); and water moving into soil is called percolation — the step that fills the groundwater stores.

The water cycle

Water bodies → Evaporation (+ transpiration from plants = evapotranspiration) → Condensation (clouds) → Rain → back into water bodies or onto land (→ seeps down → groundwater storage, the fresh water we pump out).

• The condensation step was asked directly.
• Evaporation causes cooling (asked twice, in both wordings) — the same physics as water kept in an earthen pitcher staying cool, because the pitcher’s porous build promotes evaporation and consequent cooling.

4. The atmosphere — composition and layers

• Definition (asked): the atmosphere is an envelope of air around the Earth.
• Composition: Nitrogen 78%, Oxygen 21%, other gases 1% — of which CO₂ = 0.03%, argon = 0.9% (plus helium, neon, xenon — all inside that 1%).
• Bank facts that hang on the definition: the most abundant element in the Earth’s atmosphere is nitrogen; only one planet in the solar system has an atmosphere — Earth (asked twice); if there were no atmosphere, the sky would be black (asked twice — the same answer as Chapter 1’s “no light → black sky”); if there were no CO₂ in the atmosphere, the Earth’s surface temperature would be less than the present (the greenhouse framing); in the atmosphere, high pressure indicates fair weather; and the science of the physics of the upper atmosphere is aeronomy.
• How many layers does the atmosphere have? The banks answer 5 — the four temperature layers below plus the exosphere.

The layers — the master table

Layers mnemonic: T S M T (+ E). Temperature pattern going up: decrease → increase → decrease → increase.

• Ionosphere (the other classification): 60–1,000 km, divided by electric current, not temperature. It overlaps the mesosphere and thermosphere — it is a different way of slicing the same air, not a sixth layer on top of the five.

5. Ozone — the layer, the hole, and the treaty

• The ozone layer lives in the stratosphere (20–30 km) and blocks ultraviolet rays from the Sun — that is its whole job, and the banks ask it five ways, answering ultraviolet / UV rays every time. The ozone layer plays a beneficial role for organic life on Earth.
• The banks phrase the layer’s height as “present about 30 miles (50 km) in the atmosphere above Earth” and still answer stratosphere — 50 km is the top of the stratosphere, so the layer question and the height question are the same question (see Traps).
• Ozone MCQs from the lecture: photocopier machines emit ozone (asked); International Ozone Day = 16 September (asked). The Antarctica ozone hole (7th continent) came from industrial/vehicle emissions depleting the layer.
• Bank facts that complete the picture: the gas that affects the ozone layer is CFCs (chlorofluorocarbons); and the international treaty signed in 1987 to protect the ozone layer, by phasing out the production and consumption of ozone-depleting substances, is the Montreal Protocol.

6. Master table — the three spheres at a glance

7. Rapid-fire one-liners

• Biotic → living (animals, plants, microbes); Abiotic → non-living; “a-” → opposite (ahimsa = non-violence).
• Three spheres → Lithosphere (rocks/land), Hydrosphere (water), Atmosphere (air).
• Freshwater split: ~68.7% ice caps/glaciers, ~30.1% groundwater, ~1.2% surface/other — biggest freshwater source = glaciers and ice caps.
• Renewable → land, water; Non-renewable → petroleum, coal; Petroleum = non-renewable.
• Earth interior → Crust (0–100 km, oxygen) → Mantle (to 2,900 km, magnesium + iron) → Core (to 6,378 km, nickel + iron).
• Crust boundary → Moho; crust elements → silicon, aluminium, oxygen; silicon = 27.72%; second most abundant metal = iron; crust chemistry = geochemistry.
• Oceanic crust (under the sea) vs continental crust (the land).
• Igneous rocks → from lava (fiery); Granite is igneous; Magma below, Lava above; No petroleum/coal in igneous rocks.
• Sedimentary rocks → layers from weathering + pressure; petroleum, coal, CNG, LPG found here; Porous rocks = sedimentary; Shale = sedimentary (not metamorphic).
• Metamorphic → igneous/sedimentary changed by heat and/or pressure; Rock cycle → Igneous → Sedimentary → Metamorphic.
• Volcano = crack in the crust through which hot magma and gases force out.
• Earth’s surface → 71% water, 29% land; Of all water → 97% saline, 3% fresh; only ~1% readily usable (rest in glaciers).
• Five oceans → Pacific, Atlantic, Southern, Indian, Arctic.
• Water cycle → Evaporation (+ transpiration = evapotranspiration) → Condensation → Rain → groundwater.
• Sea water saline → rivers carry soluble minerals from mountains; sea-water elements → sodium and chlorine; commonest sea salt → sodium chloride.
• Purest water → rain water; Water moving into soil → percolation; Evaporation causes cooling.
• Atmosphere → envelope of air around the Earth; Air → Nitrogen 78%, Oxygen 21%, other gases 1%; CO₂ → 0.03%; Argon → 0.9%.
• Atmosphere layers → 5; nearest layer / layer close to the surface → Troposphere; most abundant element in the atmosphere → Nitrogen.
• Troposphere → 0–16 km; airplanes, weather (short-term), climate (long-term); Lapse rate → temperature decreases 6.5°C per km.
• Stratosphere → 16–50 km; ozone layer at 20–30 km; asked as hottest layer (ozone heat).
• Mesosphere → 50–80 km; meteors appear here; temperature −3°C → −93°C.
• Thermosphere → above 80 km; satellites and spaceships; up to 1,200°C; Exosphere → beyond, no MCQs.
• Ionosphere → 60–1,000 km (by electric current, not temperature); Upper-atmosphere physics → aeronomy.
• Ozone blocks → ultraviolet rays; Photocopier machines emit → ozone; International Ozone Day → 16 September; Ozone hole → Antarctica.
• Ozone-damaging gas → CFCs; 1987 ozone treaty → Montreal Protocol.
• No atmosphere → sky black; No CO₂ → surface temperature less; High pressure in the atmosphere → fair weather; Only planet with an atmosphere → Earth.

8. Most-asked facts (from our verified past-paper banks)

• Lithosphere & Earth interior — 15 questions: the most abundant element in the Earth’s crust is oxygen (asked seven ways — the single most repeated question in this chapter); the Moho as the crust–mantle boundary; geochemistry as the crust-chemistry science; silicon 27.72% and iron as the second most abundant metal; the volcano definition; and shale as not metamorphic.
• Atmosphere & layers — 12 questions: the troposphere as the nearest layer (asked three ways); 5 layers; nitrogen as the most abundant element in the atmosphere; Earth as the only planet with an atmosphere (asked twice); black sky with no atmosphere (asked twice); aeronomy; no CO₂ → lower surface temperature; and high pressure → fair weather.
• Hydrosphere & water cycle — 9 questions: evaporation causes cooling/coolness (asked twice); purest water from rain (asked twice); sea water saline (rivers carry minerals); sodium and chlorine in sea water and sodium chloride as its commonest salt; percolation; and fresh water reserves ≈ 1.2% of total water (see Traps for how this sits with the lecture’s 3%).
• Ozone — 8 questions: ultraviolet rays blocked (asked four ways, plus the beneficial-role question); CFCs as the damaging gas; the Montreal Protocol, 1987; and the stratosphere as the ozone layer’s home (phrased at 50 km).
• Taught from the lectures, no direct site-bank question-text match: the full rock table and rock cycle, the 71/29 and 97/3 splits, the water-cycle chain with evapotranspiration, the full layer table with heights and temperatures, the lapse rate, the ionosphere, the photocopier and Ozone Day facts, and the five-ocean list — the lectures teach these at full depth, and the practice set is filtered by tags at serve time.

9. Traps & confusions

• Magma vs lava: magma is below the surface, lava is above it. Careless notes swap them — the banks ask the pair, and the lecture’s recheck corrected it to this order.
• Fresh water 3% vs 1.2%: both figures are in play and they answer different wordings. 3% is the lecture’s share of all water that is fresh; ~1% readily usable is the lecture’s usable share; the bank question worded “fresh water reserves constitute approximately ___ of total water” answers 1.2%. If the question asks the fresh share of all water, tick 3%; if it asks “fresh water reserves constitute approximately”, tick 1.2%.
• Ozone height 20–30 km vs 50 km: the ozone layer itself sits at 20–30 km inside the stratosphere; the bank question phrases it as “about 30 miles (50 km)” — the top of the stratosphere — and still answers stratosphere. Either phrasing, the layer answer is stratosphere.
• Hottest layer vs hottest temperature: the banks ask for the hottest layer and answer stratosphere (the ozone layer’s heat accumulation) — even though the thermosphere reaches 1,200°C in absolute temperature. Tick stratosphere when the question says “hottest layer”; the 1,200°C figure belongs to the thermosphere question.
• Troposphere heights 16 km vs 20 km: the lecture teaches 0–16 km (max at the equator, ~7 km at the poles) and notes some books say 20. Tick the figure in the options; 16 is the chapter’s figure.
• Shale is not metamorphic: shale is sedimentary — the trap works because students file every hard-looking rock under metamorphic. Porous rocks are sedimentary too.
• Ionosphere is not a sixth layer: it is the 60–1,000 km slice classified by electric current, overlapping the mesosphere and thermosphere. The atmosphere still has 5 layers by the temperature classification.
• Evaporation questions are water-cycle questions: “evaporation causes cooling” and the earthen-pitcher question both sit in the hydrosphere bucket — they test the cycle’s first step, not physics in general.
• Black sky, two chapters, one answer: no atmosphere → black sky appears here and in Chapter 1 (no light → black sky). Same answer, same mechanism.
• CFCs vs vehicle emissions: the lecture blames industrial/vehicle emissions for the Antarctic hole in general terms; the banks name the specific culprit gas as CFCs and the treaty as the Montreal Protocol (1987). Learn both wordings.

10. Memory tricks (lectures first, then clean professional hooks)

• T S M T (+ E): Troposphere, Stratosphere, Mesosphere, Thermosphere (+ Exosphere) — say it as a chain and the layer order is locked.
• Decrease, increase, decrease, increase: the temperature pattern going up through T–S–M–T — down in the troposphere, up in the stratosphere (ozone heat), down in the mesosphere, up in the thermosphere.
• Litho = land, Hydro = water, Atmo = air: the sphere names are the definitions — if the question names the sphere, the subject is already in the word.
• Igneous = ignition: fiery rocks from lava, like ignition from fire. Sedimentary = sediment: layers of settled debris. Metamorphic = metamorphosis: a rock changed into something else by heat and pressure.
• Magma mines below, lava lands above: magma stays below (like a mine), lava flows above — the pair the lecture’s recheck fixed, in one line.
• M with M: the Mantle holds magnesium (plus iron); the Crust holds oxygen, the Core holds nickel + iron.
• 71–97–3–1: the water chain — 71% of the surface is water, 97% of it saline, 3% fresh, ~1% readily usable. Four numbers, one chain.
• Ozone = O₃: three oxygens, one layer, one job — blocking ultraviolet. 16 September is Ozone Day: 16/9, the layer’s own date.
• Troposphere = the weather sphere: “tropo” turns — weather turns here, planes fly here, and it is the nearest layer because it is the first one you stand in.

11. Visuals (site build specs)

• DIAGRAM — The Earth’s interior cutaway: concentric Crust (0–100 km, oxygen) → Mantle (to 2,900 km, magnesium + iron) → Core (to 6,378 km, nickel + iron), with the Moho marked at the crust–mantle boundary and oceanic vs continental crust labelled — placed in Section 2 as the chapter’s orientation graphic.
• DIAGRAM — The rock cycle: a three-node loop (Igneous → weathering → Sedimentary → heat + pressure → Metamorphic → back to igneous/sedimentary), with granite, shale and the petroleum/coal/CNG/LPG note on the sedimentary node — placed in Section 2.
• DIAGRAM — The water cycle: water bodies → evaporation (+ transpiration = evapotranspiration) → condensation (clouds) → rain → percolation to groundwater, with the 71/29 and 97/3/1 figures as callouts — placed in Section 3.
• DIAGRAM — The atmosphere column: a vertical column marking T (0–16 km) → S (16–50 km, ozone band 20–30 km) → M (50–80 km) → T (above 80 km) → E, with the temperature arrows (down, up, down, up), the lapse rate on the troposphere, meteors on the mesosphere and satellites on the thermosphere, and the ionosphere band (60–1,000 km) shown as an overlapping bracket — placed in Section 4.
• INFOGRAPHIC — The three spheres at a glance: the Section 6 master table rendered as three panels (lithosphere / hydrosphere / atmosphere) for last-night revision — placed in Section 6.

12. Practice this topic

• Practice set: 44 verified past-paper questions in the PPSC + FPSC banks are tagged to this topic’s sub-topics (lithosphere & Earth interior 15, ozone 8, hydrosphere & water cycle 9, atmosphere & layers 12) — the site serves them as this chapter’s practice set, with the IBES Everyday Science capsule questions behind them. Note for the build: the practice set is filtered by the topic’s subject+topic tags at serve time, so the evaporation-cooling questions counted in the hydrosphere bucket also serve the physics revision, and the fresh-water-reserves question is served with its bank wording (1.2%) alongside the lecture’s 3% fresh share.
• Book mode: ← Previous: The Universe & the Solar System · Next: Human Body & Health (Everyday Science) →

Goldmine Notes · Everyday Science · Chapter 2 · Sources: EDS Lecture 2 (Spheres — detailed notes, rechecked; food-science half cross-linked to Chapter 5, not repeated here); EDS Lecture 1 Section 11 (Earth interior: crust/mantle/core); verified PPSC/FPSC past-paper banks (44 topic questions, script-counted, hidden_files/goldmine-notes-count-eds02.py); IBES Everyday Science capsule bank behind the chapter. Standard answers only.