World physical geography is the branch of geography that studies the natural form and processes of the Earth: the structure of its interior, the movement of its tectonic plates, the sculpting of mountains, plateaus and plains, the circulation of oceans and the atmosphere, and the global pattern of climate. For judiciary and CLAT-PG aspirants, this is overwhelmingly a factual-recall subject. Examiners reward precise figures (the depth of the Moho, the height of Everest, the share of the atmosphere that is nitrogen) and clean conceptual distinctions (igneous versus metamorphic rock, convergent versus divergent plate margins). This chapter consolidates the high-yield core of world physical geography, ties each fact to a verified figure, and flags the comparisons that examiners love to test. It pairs closely with our notes on the universe and solar system and the physical features of India; for the full syllabus map see the Geography for Judiciary hub.
The Shape and Dimensions of the Earth
The Earth is not a perfect sphere but an oblate spheroid (or, more precisely, a geoid): it bulges slightly at the Equator and is flattened at the poles because of its rotation. The equatorial diameter is about 12,756 km, while the polar diameter is about 12,714 km, a difference of roughly 42 km. The equatorial circumference is approximately 40,075 km and the polar circumference about 40,008 km. The mean radius is close to 6,371 km, a figure worth memorising because seismic depths (Moho, Gutenberg, Lehmann discontinuities) are usually quoted as distances downward from the surface toward this centre.
The Earth performs two principal motions. Rotation on its axis takes about 23 hours 56 minutes (one sidereal day) and produces day and night; the axis is tilted at 23.5 degrees to the perpendicular of the orbital plane, which together with revolution around the Sun (about 365.25 days) produces the seasons. The 0.25-day surplus is corrected by adding a leap day every fourth year. These motions, and the Earth's place in the wider cosmos, are developed in the companion chapter on the universe and solar system.
The Interior of the Earth and Seismic Discontinuities
Because the deepest borehole (the Kola Superdeep Borehole, about 12 km) barely scratches the surface, our knowledge of the Earth's interior comes overwhelmingly from seismic waves. Primary (P) waves are longitudinal and travel through solids, liquids and gases; secondary (S) waves are transverse and cannot pass through liquids. The behaviour of these waves reveals the planet's layered structure. The Earth is divided into three broad layers: the crust, the mantle and the core.
The crust is the thin outermost shell, averaging about 30 to 35 km under the continents (thicker beneath high mountains) but only about 5 to 8 km under the oceans. Continental crust is largely granitic (the silica-and-aluminium rich SIAL), while oceanic crust is basaltic (the silica-and-magnesium rich SIMA). The boundary between crust and mantle is the Mohorovicic discontinuity (the Moho), discovered by Andrija Mohorovicic in 1909, where the velocity of seismic waves jumps sharply.
Below the Moho the mantle extends to a depth of about 2,900 km. The Gutenberg discontinuity, at roughly 2,900 km, marks the mantle-core boundary; here P-waves slow and S-waves vanish entirely, proving that the outer core is liquid. The core itself runs from about 2,900 km to the centre at 6,371 km. The outer core is molten iron and nickel and is the seat of the Earth's magnetic field through the dynamo effect; the Lehmann discontinuity at about 5,150 km separates it from a solid inner core. The combined iron-nickel core is sometimes called the NIFE layer.
Continental Drift and Plate Tectonics
In 1912 the German meteorologist Alfred Wegener proposed the theory of continental drift, arguing that all the present continents were once united in a single supercontinent he named Pangaea ("all land"), surrounded by a universal ocean called Panthalassa. Pangaea, he said, began to break apart about 200 million years ago into a northern landmass, Laurasia, and a southern landmass, Gondwanaland. Wegener's evidence included the jigsaw fit of the coastlines of South America and Africa, matching fossils such as Mesosaurus on both continents, and correlated rock structures. His weakness was the lack of a credible mechanism, which left the theory contested for decades.
That gap was filled by the theory of plate tectonics, which emerged in the 1960s and absorbed continental drift. The Earth's rigid outer shell, the lithosphere, is broken into several major plates (the Pacific, North American, South American, Eurasian, African, Indo-Australian and Antarctic) that float on the plastic asthenosphere and move a few centimetres a year, driven largely by mantle convection currents. The Indian plate's northward collision with the Eurasian plate is the engine behind the Himalayas, a process examined further in the chapter on India's physical features.
Plate Boundaries, Earthquakes and the Ring of Fire
Plate margins are of three types, and almost all of the world's earthquakes and volcanoes occur along them. At divergent (constructive) boundaries plates move apart and magma rises to form new crust; the classic example is the Mid-Atlantic Ridge, where Iceland sits astride the spreading axis. At convergent (destructive) boundaries plates move toward each other: where an oceanic plate meets a continental one the denser oceanic plate is forced down in a subduction zone, creating deep trenches and volcanic arcs, while two continental plates collide to throw up fold mountains like the Himalayas. At transform (conservative) boundaries plates slide horizontally past one another, generating earthquakes but no new crust; the San Andreas Fault in California is the textbook case.
The seismic focus (the point of rupture underground) is the hypocentre, and the point directly above it on the surface is the epicentre. Earthquake magnitude is measured on the Richter scale (energy released, logarithmic) and intensity on the Mercalli scale (observed effects). The horseshoe-shaped belt of subduction zones rimming the Pacific, the Ring of Fire, accounts for the great majority of the world's earthquakes and active volcanoes. Volcanoes are classified by activity (active, dormant, extinct) and by form (shield, composite or stratovolcano, cinder cone, and caldera), distinctions frequently tested in objective papers.
Rocks, Minerals and the Rock Cycle
The crust is built of rocks, aggregates of minerals, of which there are three primary classes. Igneous rocks form when molten magma or lava cools and solidifies; granite (intrusive, slow-cooling, coarse-grained) and basalt (extrusive, fast-cooling, fine-grained) are the standard examples, and the term igneous derives from the Latin ignis, meaning fire. Sedimentary rocks form by the deposition, compaction and cementation of sediments or by chemical precipitation; sandstone, limestone, shale and coal are typical, and these are the rocks in which fossils and most fossil fuels are found. Metamorphic rocks form when pre-existing rocks are transformed by heat and pressure without melting: limestone becomes marble, sandstone becomes quartzite, shale becomes slate, and granite becomes gneiss.
These three classes are linked by the rock cycle: igneous rock can weather into sediment that lithifies into sedimentary rock, which can be metamorphosed and ultimately melted back into magma, closing the loop. Examiners reliably test the parent-product pairs (limestone to marble, coal to graphite to diamond under extreme conditions), so these should be memorised as matched pairs. The economic minerals locked in these rocks connect this topic to the chapter on the natural resources of India.
Major Landforms: Mountains, Plateaus and Plains
The Earth's surface relief is built around three first-order landforms. Mountains are classified by origin into fold mountains (the Himalayas, Alps, Andes and Rockies, formed by compression of sediments at convergent margins), block mountains or horsts (the Vosges and Black Forest, formed by faulting, with intervening sunken blocks called grabens or rift valleys), volcanic mountains (Mount Kilimanjaro, Mount Fuji), and residual mountains sculpted by erosion (the Aravallis, among the world's oldest). The Himalayas are the youngest and highest fold mountains; the Andes are the longest continental mountain range.
The highest point on Earth is Mount Everest (Sagarmatha / Chomolungma) in the Himalayas, standing about 8,849 metres above sea level. Plateaus are elevated flatlands: the Tibetan Plateau is the highest and most extensive (the "Roof of the World"), while the Deccan Plateau is a classic lava plateau. Plains, formed mostly by the deposition of sediment by rivers, glaciers, wind or waves, are the most densely populated landforms because of their fertile alluvial soils; the Indo-Gangetic Plain is the prime South Asian example, developed in the chapter on India's physical features.
The Oceans and the Relief of the Ocean Floor
About 71 percent of the Earth's surface is covered by water, and the five oceans, in descending order of size, are the Pacific, the Atlantic, the Indian, the Southern (Antarctic) and the Arctic. The Pacific is by far the largest and deepest. The ocean floor is not a featureless basin; from the coast outward it comprises the gently sloping continental shelf (richest in marine life and petroleum), the steeper continental slope, the vast flat abyssal plain, and the great oceanic trenches.
The deepest point on Earth is the Challenger Deep in the Mariana Trench in the western Pacific, at roughly 10,900 to 11,000 metres below sea level, deeper than Everest is tall, so that if Everest were dropped into the trench its summit would remain over two kilometres underwater. Mid-ocean ridges, the longest mountain systems on the planet, mark the divergent boundaries where new oceanic crust is created. The salinity of ocean water averages about 35 parts per thousand, a figure examiners pair with named seas such as the highly saline Dead Sea and the brackish Baltic Sea. Salinity is highest in enclosed, hot, low-rainfall seas where evaporation exceeds inflow, and lowest where great rivers or melting ice dilute the water. The four-fifths of the seabed that lies between 3,000 and 6,000 metres deep, the abyssal plains, are among the flattest and least explored surfaces on Earth, mantled in fine ooze and dotted with submarine volcanoes called seamounts.
Ocean Currents, Tides and El Nino
Ocean water is in constant motion. Currents are large-scale flows driven by prevailing winds, the Earth's rotation and differences in temperature and salinity. They are deflected by the Coriolis effect, to the right in the Northern Hemisphere and to the left in the Southern, producing clockwise gyres in the north and anticlockwise gyres in the south. Warm currents such as the Gulf Stream and its extension the North Atlantic Drift carry tropical heat poleward and keep north-west Europe mild; cold currents such as the Humboldt (Peru) Current and the Labrador Current bring nutrient-rich upwelling and rich fisheries. Where warm and cold currents meet, as off Newfoundland (the Grand Banks) or Japan, fog and exceptional fishing grounds result.
The periodic warming of the central and eastern Pacific known as El Nino, part of the El Nino Southern Oscillation, occurs when the trade winds weaken and the warm western Pacific pool spreads eastward, suppressing the cold Humboldt upwelling and disrupting global weather, including the Indian monsoon. Its cold-phase counterpart is La Nina. Tides, the periodic rise and fall of sea level, are caused by the gravitational pull of the Moon and the Sun; the largest spring tides occur at full and new moon when Sun and Moon align, while the smallest neap tides occur at the quarter moons.
The Atmosphere: Structure and Composition
The atmosphere is the gaseous envelope of the Earth. By volume the dry atmosphere is about 78 percent nitrogen and about 21 percent oxygen, with argon, carbon dioxide and trace gases making up the remaining one percent; water vapour and dust are variable. It is divided into layers by temperature behaviour. The troposphere, the lowest layer, extends to about 8 km at the poles and up to about 18 km at the Equator (about 12 km on average); almost all weather occurs here and temperature falls with height at the normal lapse rate of roughly 6.5 degrees Celsius per kilometre.
Above it lies the stratosphere, reaching to about 50 km, which contains the ozone layer (concentrated at roughly 15 to 35 km) that absorbs harmful ultraviolet radiation and within which temperature rises with height, making it stable and ideal for jet aircraft. The mesosphere extends to about 85 km and is the coldest layer, where meteors burn up. The thermosphere above it, containing the ion-rich ionosphere that reflects radio waves, sees temperatures climb steeply, and beyond it the exosphere fades into space. The boundary tops are named the tropopause, stratopause and mesopause.
Weather, Climate and the Global Wind System
Weather is the moment-to-moment state of the atmosphere at a place, while climate is the average of weather over a long period, conventionally about thirty years. Insolation (incoming solar radiation) is the ultimate driver, and because the Sun's rays strike the Equator nearly vertically and the poles obliquely, the tropics receive far more heat, setting up the pressure differences that drive global winds.
The planetary wind system arises from permanent pressure belts: the equatorial low (the doldrums or Inter-Tropical Convergence Zone), the sub-tropical highs near 30 degrees, the sub-polar lows near 60 degrees, and the polar highs. Between them blow the trade winds (from the sub-tropical highs toward the Equator, deflected by the Coriolis force to become the north-east and south-east trades), the westerlies (toward the poles, the roaring forties of the Southern Ocean), and the polar easterlies. Monsoons are seasonally reversing winds caused by the differential heating of land and sea; the South-West Monsoon that waters the subcontinent is the dominant feature of India's climate and monsoon.
Humidity, Clouds and Types of Rainfall
Humidity is the amount of water vapour in the air; relative humidity expresses it as a percentage of the maximum the air can hold at that temperature. When moist air is cooled to its dew point the vapour condenses around tiny particles to form clouds. Clouds are classified by height and form into high clouds (cirrus, cirrostratus, cirrocumulus), middle clouds (altostratus, altocumulus), low clouds (stratus, stratocumulus, nimbostratus) and the towering vertical cumulonimbus, the thunderstorm cloud.
Rainfall is produced when condensation droplets coalesce until they are heavy enough to fall, and three mechanisms are distinguished. Convectional rainfall results from intense surface heating that drives moist air upward, typical of equatorial afternoons. Orographic (relief) rainfall occurs when moist winds are forced to rise over mountains, drenching the windward slope and leaving a dry rain shadow on the leeward side, the classic example being the Western Ghats. Cyclonic (frontal) rainfall occurs along the boundary between warm and cold air masses in temperate depressions. A fourth, hybrid pattern, the seasonal monsoon rains of South Asia, combines orographic uplift against the Western Ghats and the Himalayas with the large-scale convergence of moist maritime air, which is why Mawsynram and Cherrapunji in the Khasi Hills record some of the heaviest rainfall on Earth. These mechanisms underpin the regional rainfall patterns analysed in the chapter on India's climate and monsoon.
World Climatic Regions and Natural Vegetation
Geographers group the world's climates into broad belts, most famously through the Koppen classification, which uses temperature and precipitation thresholds to define types lettered A (tropical), B (dry), C (temperate), D (cold continental) and E (polar). Each climatic region supports a characteristic biome of natural vegetation. The hot, wet equatorial belt grows dense evergreen rainforest (the Amazon, the Congo, and South-East Asia), the most biodiverse vegetation on Earth.
The seasonally dry tropical savanna supports tall grasses and scattered trees and is famed for African wildlife; the hot desert climate of the Sahara, Arabian and Thar regions supports only xerophytic scrub. In the mid-latitudes, the Mediterranean climate of dry summers and wet winters grows drought-resistant evergreen shrub, the temperate grasslands (the prairies, steppes, pampas and veld) are the world's great wheat and cattle belts, and the cold continental interiors carry the vast coniferous taiga. Beyond the tree line lies the treeless tundra, and at the highest latitudes the permanent ice of the polar caps. These global vegetation belts frame the more detailed study of India's biogeography in the chapter on the natural resources of India.
Rivers, Glaciers and the Agents of Erosion
The face of the land is continuously reshaped by external agents of gradation, the twin processes of weathering (the in-place breakdown of rock) and erosion (its removal and transport). Rivers are the most important agent over most of the globe. In their youthful upper course they cut V-shaped valleys, gorges and waterfalls; in the mature middle course they meander; and in old age they deposit floodplains, levees and, at the sea, deltas (such as the Ganga-Brahmaputra Sundarbans delta) or estuaries. The world's longest rivers are the Nile in Africa and the Amazon in South America, the latter carrying by far the greatest volume of water; India's network is the focus of the chapter on Indian river systems and drainage.
Glaciers are slow-moving rivers of ice that carve U-shaped valleys, cirques, aretes, hanging valleys and fjords, and deposit unsorted debris called moraine. Wind, the chief agent in deserts, sculpts mushroom rocks, yardangs and shifting sand dunes, and deposits fine wind-blown silt as fertile loess. Groundwater dissolves limestone to create karst topography with caves, stalactites and stalagmites, and the sea carves cliffs, caves, arches and stacks while building beaches and spits. Each agent leaves a distinctive suite of erosional and depositional landforms that objective papers test as matched pairs.
Latitude, Longitude and Time Zones
Position on the globe is fixed by a grid of latitudes and longitudes. Latitudes are parallel circles measured north and south of the Equator (0 degrees) up to 90 degrees at the poles; the key parallels are the Tropic of Cancer (23.5 degrees North), the Tropic of Capricorn (23.5 degrees South), and the Arctic and Antarctic Circles (66.5 degrees). Longitudes are semicircles (meridians) running pole to pole, measured east and west of the Prime Meridian (0 degrees) at Greenwich up to 180 degrees.
Because the Earth rotates 360 degrees in 24 hours, it turns 15 degrees of longitude every hour, so local time advances by four minutes for every degree of longitude eastward. Greenwich Mean Time is the reference, and the International Date Line near 180 degrees marks where the calendar date changes. India keeps a single standard time, Indian Standard Time, based on the 82.5 degrees East meridian passing near Mirzapur, which is 5 hours 30 minutes ahead of GMT, a fact that bridges this chapter to the study of India's political map and states.
Frequently asked questions
What is the Mohorovicic discontinuity and why does it matter?
The Moho, discovered by Andrija Mohorovicic in 1909, is the boundary between the Earth's crust and mantle, where seismic wave velocity jumps sharply. It lies about 30 to 35 km below the continents but only 5 to 8 km below the oceans. It is a high-frequency exam fact, usually tested alongside the Gutenberg discontinuity (mantle-core boundary at about 2,900 km) and the Lehmann discontinuity (outer-inner core boundary at about 5,150 km).
Who proposed continental drift and how does it differ from plate tectonics?
Alfred Wegener proposed continental drift in 1912, holding that the continents once formed a single supercontinent, Pangaea, surrounded by the ocean Panthalassa. He offered strong evidence (coastline fit, matching fossils such as Mesosaurus) but no convincing mechanism. Plate tectonics, developed in the 1960s, supplied that mechanism, mantle convection moving lithospheric plates, and absorbed continental drift into a complete theory of the lithosphere.
Which is the deepest point on Earth, and how does it compare with Mount Everest?
The deepest point is the Challenger Deep in the Mariana Trench in the western Pacific, at roughly 10,900 to 11,000 metres below sea level. Mount Everest, the highest point on land, rises about 8,849 metres above sea level. The trench is deeper than Everest is tall, so dropping Everest into the Challenger Deep would still leave its summit more than two kilometres underwater.
What are the three types of rocks and their parent-product pairs?
The three classes are igneous (cooled magma or lava, e.g. granite and basalt), sedimentary (deposited and cemented sediments, e.g. sandstone, limestone and coal), and metamorphic (rocks transformed by heat and pressure). Examiners test the metamorphic pairs as matched sets: limestone becomes marble, sandstone becomes quartzite, shale becomes slate, granite becomes gneiss, and coal becomes graphite. All three are linked by the rock cycle.
What is the composition and layering of the atmosphere?
By volume the dry atmosphere is about 78 percent nitrogen and about 21 percent oxygen, with argon and carbon dioxide in the remaining one percent. Its layers by temperature are the troposphere (weather layer, up to about 18 km at the Equator), the stratosphere (to about 50 km, holding the ozone layer), the mesosphere (to about 85 km, the coldest layer), the thermosphere (containing the radio-reflecting ionosphere), and the exosphere.
What causes the Coriolis effect and El Nino?
The Coriolis effect is the apparent deflection of moving air and water caused by the Earth's rotation, to the right in the Northern Hemisphere and to the left in the Southern, which steers winds and ocean gyres. El Nino is the periodic warming of the central and eastern Pacific that occurs when the trade winds weaken and the warm western-Pacific pool spreads eastward, suppressing the cold Humboldt upwelling and disrupting global weather including the Indian monsoon; its cold counterpart is La Nina.