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Glossary Terms
| Term (EN) | Definition | Exam Relevance |
|---|---|---|
| Sial | Continental crust layer — Silica + Aluminium, density 2.7 g/cm³ | PYQ 2021 — 2 marks |
| Sima | Oceanic crust + crust base — Silica + Magnesium, density 3.0 g/cm³ | PYQ 2021 — 2 marks |
| Mohorovičić Discontinuity | Crust-mantle boundary at ~35 km; P-wave velocity increase | Interior structure 5-mark |
| Gutenberg Discontinuity | Mantle-outer core boundary at 2,900 km | Interior structure 5-mark |
| Lehmann Discontinuity | Outer core–inner core boundary at 5,100 km | Interior structure 5-mark |
| Asthenosphere | Partially molten mantle zone (100–350 km); enables plate movement | Plate tectonics 5-mark |
| Lithosphere | Rigid crust + uppermost solid mantle (~100 km); forms tectonic plates | Plate tectonics 5-mark |
| Geodynamo | Liquid outer core circulation generating Earth's magnetic field | Core 5-mark |
| P-waves | Primary/compressional seismic waves; travel through all media | Interior study method |
| S-waves | Secondary/shear seismic waves; travel only through solids | Proves outer core is liquid |
| Shadow Zone | Zone 103°–143° from earthquake where P-waves are absent | Earth interior evidence |
| Geological Time Scale | Standardised chronological framework dividing Earth's history into eons, eras, periods | Direct exam topic |
| Mesozoic Era | 252–66 Ma; Age of Reptiles/Dinosaurs | PYQ 2021 — 2 marks |
| Carboniferous | Period 359–299 Ma; coal-forming swamp forests; first reptiles | PYQ 2023 — 5 marks |
| Gondwana | Southern supercontinent including India, Africa, Australia, Antarctica | India's geological history |
| Pangaea | Single supercontinent ~270 Ma; broke into Laurasia (north) + Gondwana (south) | Plate tectonics |
| Igneous Rock | Rock formed by cooling of magma/lava (granite, basalt) | Rock cycle |
| Sedimentary Rock | Rock formed by compaction of sediments; contains fossils and fossil fuels | Coal, petroleum source |
| Metamorphic Rock | Rock transformed by heat/pressure (marble, quartzite, slate) | Rajasthan marble |
| Isostasy | Gravitational equilibrium of crust "floating" on denser mantle | Mountains have deep roots |
| Palaeozoic Era | 541–252 Ma; Ancient Life; 6 periods; Cambrian explosion to P-T extinction | Background context |
| Cenozoic Era | 66 Ma–present; Age of Mammals; includes Quaternary Ice Ages and Holocene | Background context |
| K-Pg Extinction | 66 Ma; Chicxulub asteroid; 75% species extinct; end of dinosaurs | Mass extinction 5-mark |
| Tethys Sea | Ancient ocean between Gondwana and Laurasia; closed as India collided with Asia, forming Himalayas | Himalayan origin |
| Holocene | Current geological epoch (12,000 BP–present); warm interglacial; human civilisation | Current context |
Sources: International Commission on Stratigraphy (ICS) 2024 Geological Time Scale; USGS Interior of the Earth; RPSC Mains PYQ 2013–2023; NCERT Geography Textbooks (Class XI Physical Geography); Strahler: Physical Geography; Hussain: Geography of India.