Unit III, Part A: World Geography and Geology

What the official syllabus says

RAS Mains Paper II, Unit III - Earth Science (Geography & Geology), Part A - World

• Interior of the Earth and Geological Time Scale.
• Broad Physical Features: Mountains, Plateaus, Plains, Deserts - types and distribution.
• Earthquakes and Volcanoes: Types, distribution and their impact.
• Climate - Insolation, Atmospheric circulation, Humidity and Precipitation.
• Major Environmental Issues.

Topics in detail

Interior of the Earth

• Sources of information: seismic waves, volcanic material, meteorites, gravity and magnetism, deep drilling.
• Seismic waves: P waves (pass through solids and liquids), S waves (solids only), surface waves; the shadow zone and what it tells us about the liquid outer core.
• Layers: crust (continental and oceanic; sial and sima), mantle (including the asthenosphere), outer core (liquid) and inner core (solid); the lithosphere as the crust plus the uppermost mantle.
• Discontinuities: Conrad, Mohorovicic (crust and mantle), Repetti, Gutenberg (mantle and core) and Lehmann (outer and inner core).
• Composition, temperature, pressure and density with depth.

Geological time scale

• Eons, eras, periods and epochs; how rocks and fossils are dated (relative and radiometric dating).
• Precambrian: formation of the Earth, the oldest rocks, early life.
• Palaeozoic (Cambrian to Permian): explosion of life, first land plants, fishes, amphibians, coal-forming forests.
• Mesozoic (Triassic, Jurassic, Cretaceous): age of reptiles and dinosaurs; break-up of Pangaea.
• Cenozoic (Palaeogene, Neogene, Quaternary): rise of mammals, rise of the Himalayas, ice ages and humans.
• Continental drift, sea-floor spreading and plate tectonics as the framework for all landforms.

Broad physical features: types and distribution

• Mountains: fold mountains (Himalayas, Alps, Andes, Rockies), block mountains (Vosges, Black Forest), volcanic mountains (Kilimanjaro, Fuji), residual mountains (Aravallis); young and old mountains.
• Plateaus: intermontane (Tibet), piedmont, continental (Deccan), volcanic and lava plateaus; their economic importance.
• Plains: structural, erosional and depositional (alluvial, deltaic, glacial, loess plains); major plains of the world.
• Deserts: hot trade-wind deserts (Sahara, Arabian, Kalahari, Thar, Australian), mid-latitude deserts (Gobi, Patagonian), coastal deserts formed by cold currents (Atacama, Namib); desert landforms (dunes, playas, mushroom rocks, inselbergs).

Earthquakes and volcanoes

• Earthquakes: focus and epicentre; causes (plate movement, faulting, volcanic activity, human-induced); magnitude (Richter and moment magnitude) and intensity (Mercalli).
• Distribution: the circum-Pacific belt, the Alpine-Himalayan belt, mid-oceanic ridges; seismic zones of India.
• Impact: ground shaking, landslides, tsunamis, liquefaction; earthquake-resistant building and preparedness.
• Volcanoes: shield, composite (strato), cinder cone and caldera; active, dormant and extinct volcanoes.
• Volcanic landforms: intrusive (batholith, laccolith, sill, dyke) and extrusive (lava plateaus, cones, craters).
• Distribution: the Pacific Ring of Fire, mid-Atlantic ridge, hotspots (Hawaii); Barren Island in India.
• Impact: destruction and loss of life, effects on climate, fertile soils, geothermal energy.

Climate

• Insolation: factors affecting it (angle of the Sun, length of day, distance, atmosphere); heat budget of the Earth; albedo; temperature inversion.
• Atmospheric circulation: pressure belts, planetary winds (trade winds, westerlies, polar easterlies), the three-cell model (Hadley, Ferrel and polar cells), the ITCZ and its shift.
• Jet streams, monsoons, local winds (loo, foehn, chinook, mistral, sirocco); El Nino, La Nina and the Southern Oscillation.
• Air masses, fronts, tropical and temperate cyclones.
• Humidity: absolute, relative and specific humidity; dew point; condensation (dew, frost, fog, clouds).
• Precipitation: forms (rain, snow, sleet, hail) and types (convectional, orographic, cyclonic or frontal); world distribution of rainfall.
• Climatic classification of the world (Koppen) in outline.

Major environmental issues

• Climate change and global warming: greenhouse gases, impacts on glaciers, sea level, agriculture and health; UNFCCC, the Kyoto Protocol and the Paris Agreement.
• Ozone layer depletion: causes (CFCs) and the Montreal Protocol.
• Desertification and land degradation: causes, the UN Convention to Combat Desertification.
• Deforestation and loss of biodiversity: the Convention on Biological Diversity; biodiversity hotspots.
• Air, water, soil and plastic pollution; acid rain; e-waste.
• Water scarcity and groundwater depletion; natural disasters and their link with environmental degradation.

Overlaps

World physical features and environmental issues are also in the Prelims Geography of World and India section: see RAS Prelims.