Geomorphology and Earth Structure

The question is built on the standard division of geomorphic agencies into exogenic forces, driven by solar energy and gravity, and endogenic forces, driven by the earth's internal heat.

• Item 1, electromagnetic radiation, is the solar input that drives insolation, differential heating, winds, the hydrological cycle and therefore all weathering, erosion and deposition, so it qualifies.
• Item 2, geothermal energy, is the internal heat that drives mantle convection, volcanism and metamorphism, and is the ultimate source of all endogenic activity.
• Item 3, gravitational force, drives mass movement, the flow of rivers and glaciers, the settling of sediment and, in the form of tidal force, coastal work, and it is also the force behind isostatic adjustment.
• Item 4, plate movements, produce mountain building, rifting, earthquakes and volcanoes, and are the most obviously qualifying item in the set.
• Item 5, rotation, generates the Coriolis effect, which organises the planetary wind belts and ocean gyres, and produces tides in combination with lunar and solar attraction, so it operates on the surface at one remove.
• Item 6, revolution, in combination with axial tilt produces the seasons, and therefore the seasonal rhythm of glacial melt, monsoon rainfall, freeze and thaw and river regime; over long periods the orbital variations of the Milankovitch cycles govern glacial and interglacial phases and the associated eustatic changes of sea level. On this reading all six qualify and the official answer is (d). The structure of the option set gives the elimination route: no option omits item 1 or item 4 together, and once a candidate accepts that rotation and revolution both operate indirectly, only (d) contains everything.

• Pairs 3 and 4 are correctly matched and pairs 1 and 2 are not, so the official answer is (c). The Mahadeo Hills are part of the Satpura system in Madhya Pradesh, containing Pachmarhi and the highest point of the Satpura range at Dhupgarh, and are correctly placed in central India. The Mikir Hills, now more commonly the Karbi Anglong hills, are an outlier of the peninsular block lying south of the Brahmaputra in Assam, and are correctly placed in the north-east.
• Pair 1 is incorrectly matched: the Cardamom Hills are the southernmost section of the Western Ghats, spanning Kerala and Tamil Nadu, and belong to the western side of the peninsula, whereas the Coromandel Coast is the eastern seaboard south of the Krishna delta.
• Pair 2 is incorrectly matched and is the reverse error: the Kaimur Hills are the eastern extension of the Vindhyan range running through Bihar, Uttar Pradesh and Madhya Pradesh, entirely inland, whereas the Konkan is the western coastal strip between Daman and Goa. The item is efficiently solved because the two false pairs are false in the same way, each transposing an interior or western feature to the wrong coast, and rejecting either pair 1 or pair 2 leaves only options that must be tested against the remaining pair.

• Pair 1 is correct. Srisailam, seat of the Mallikarjuna jyotirlinga, stands on the Krishna within the Nallamala Hills of the Eastern Ghats in Andhra Pradesh.
• Pair 2 is incorrect. Omkareshwar, also a jyotirlinga, is on Mandhata island in the Narmada in Madhya Pradesh, in the trough between the Vindhya and Satpura ranges, whereas the Satmala Hills are part of the Sahyadri offshoots in the Nashik region of Maharashtra.
• Pair 3 is incorrect. Pushkar, with its Brahma temple, lies in the Aravalli near Ajmer in Rajasthan, while the Mahadeo Hills are a section of the Satpura in Madhya Pradesh containing Pachmarhi and Dhupgarh. The official answer (a) follows. Elimination route is clean and single step: Pushkar's location in the Aravalli is common knowledge, and rejecting pair 3 eliminates options (b), (c) and (d) together, leaving (a) without any need to place the Satmala Hills.

• Statement 1 is incorrect. The Himalayas extend across far more than five States and Union Territories, running through Jammu and Kashmir and Ladakh, Himachal Pradesh, Uttarakhand, Sikkim, West Bengal in its northern districts, and Arunachal Pradesh, with the associated ranges extending into the north eastern States. On any reasonable reckoning the count exceeds five.
• Statement 2 is incorrect. The Western Ghats run through six States, Gujarat at their northern extremity in the Dangs, then Maharashtra, Goa, Karnataka, Kerala and Tamil Nadu. The count of five is obtained only by omitting Gujarat, which is precisely the omission the statement is built on, and the UNESCO World Heritage serial inscription of 2012 covers sites across six States.
• Statement 3 is correct. Pulicat Lake, the second largest brackish water lagoon in India, lies across the Andhra Pradesh and Tamil Nadu boundary, with much the greater part in Andhra Pradesh and the southern portion, including the Sriharikota barrier, straddling the line into Tamil Nadu. Two States, and no more. Rejecting statement 1 eliminates (a) and (d), and rejecting statement 2 then eliminates (c), leaving (b). Governing principle: every statement here turns on the word 'only', and each of the two false ones fails by a single omitted State or region. Count the units at the margins of a feature, since that is where these items are constructed.

• Statement 2 is incorrect and it is the obvious reject that opens the question. The early Earth had essentially no free oxygen. Its primordial atmosphere was lost, and the secondary atmosphere produced by degassing of the interior was dominated by water vapour, carbon dioxide, nitrogen, methane and ammonia. The statement inverts the actual composition on both counts, asserting abundant oxygen and absent carbon dioxide when the truth is the reverse, and the figure of 54 per cent has no basis. Free oxygen is a product of life, not a precondition for it.
• Statement 3 is correct and follows directly. Photosynthesising cyanobacteria released oxygen, which was first consumed by dissolved iron and by reduced minerals, producing the banded iron formations, and only when those sinks were exhausted did oxygen accumulate in the atmosphere in the Great Oxidation Event around 2400 million years ago. That accumulation in turn created the ozone screen and made the colonisation of land possible, so the biosphere reconstructed the atmosphere it now depends on.
• Statement 1 is correct as the key takes it. Reversals of the geomagnetic field are recorded in the magnetisation of successive lavas and in the symmetrical magnetic striping of the ocean floor about the mid ocean ridges, which was the decisive evidence for sea floor spreading, and the most recent full reversal, the Brunhes Matuyama, was about 780,000 years ago. So statements 1 and 3 are correct and the answer is (c). Elimination route: rejecting statement 2 removes options (b) and (d) at once, leaving (a) against (c), and statement 3 is then almost self evidently true for anyone who knows that atmospheric oxygen is biogenic.

Hence (c).

• Statement 1 is correct. Barren Island is the only confirmed active volcano in South Asia and lies within Indian territory, in the Andaman Sea, on the volcanic arc produced by the subduction of the Indian plate beneath the Burma plate; the same arc carries Narcondam, which is classified as dormant.
• Statement 2 is incorrect on both the distance and the direction. Barren Island lies roughly 135 to 140 kilometres north east of Port Blair, which is in the Andaman group, whereas Great Nicobar is the southernmost island of the Nicobar group, several hundred kilometres to the south. The number in the statement is borrowed from the true distance and attached to the wrong reference point, which is the trap.
• Statement 3 is incorrect. After a long dormancy from 1803 the volcano resumed activity in 1991, but it has erupted repeatedly since, with episodes in 1994 and 1995, in 2005 following the great Sumatra Andaman earthquake, and again in 2017, when a National Institute of Oceanography vessel observed lava and ash emission at close quarters. Elimination route: statement 1 is standard and secure, which removes options (b) and (c); the choice between (a) and (d) then rests on statement 3, and a candidate who followed the 2017 reports rejects it directly.

Hence (a).

• Pair 1 is incorrectly matched. Namcha Barwa stands at the eastern extremity of the Himalaya in Tibet, marking the syntaxial bend where the Tsangpo turns south through its great gorge to become the Siang and then the Brahmaputra. It lies far to the east of the Garhwal Himalaya, which occupies the western part of Uttarakhand.
• Pair 2 is correctly matched. Nanda Devi, the highest peak lying wholly within India, is in the Kumaon Himalaya of eastern Uttarakhand and gives its name to the surrounding national park and biosphere reserve.
• Pair 3 is incorrectly matched. Nokrek is the highest point of the Garo Hills in Meghalaya, part of the Meghalaya plateau of the peninsular block, and is known chiefly as a biosphere reserve with wild citrus germplasm. It is neither in Sikkim nor in the Himalaya at all, which is the sharper error. Only pair 2 stands, giving (b); options (a) and (c) admit the misplaced Namcha Barwa, and (c) and (d) admit the misplaced Nokrek.

• Statement 1 is incorrect. Amarkantak in Madhya Pradesh lies where the Vindhya, Satpura and Maikal ranges meet, and is the source region of the Narmada and Son. The Sahyadri is the Western Ghats and is nowhere near it.
• Statement 2 is incorrect. The Biligirirangan Hills lie in southern Karnataka and form a link between the Western Ghats and the Eastern Ghats, not any part of the Satpura, which is a central Indian range.
• Statement 3 is incorrect. The Seshachalam Hills are in Andhra Pradesh and belong to the Eastern Ghats, and are known for red sanders. The southernmost extent of the Western Ghats is around the Agasthyamalai and the Cardamom Hills. All three fail, giving (d). Any of (a), (b) or (c) would require at least one of these misplacements to be accepted.

Both statements are correct.

• Statement 1 follows from the fact that P waves are the faster body waves, travelling at roughly six kilometres per second in the crust against about three and a half for S waves, so they arrive first, which is why they are called primary waves. The widening gap between the P and S arrivals with distance is used to locate the epicentre and is the basis of early warning systems.
• Statement 2 states the physical distinction correctly. P waves are longitudinal or compressional, with particle motion parallel to the direction of propagation through alternating compression and rarefaction, and they therefore propagate through solids, liquids and gases. S waves are transverse, with particle motion perpendicular to propagation, which requires shear rigidity and is why they cannot travel through the liquid outer core, producing the S wave shadow zone.

Hence (c).

• Statement-II is correct. Atmospheric carbon dioxide dissolves in rain water to form carbonic acid, which drives carbonation, the chemical weathering process that dissolves limestone and decomposes feldspar.
• Statement-III is correct. Rain water carries dissolved atmospheric oxygen, which drives oxidation, the weathering process that converts ferrous minerals to ferric oxides and produces the reddish crusts and crumbling seen in iron rich rocks. Both processes are recognised forms of chemical weathering, so both statements explain Statement-I, giving (a).
• Option (b) fails because there is no basis for excluding either process.
• Option (c) fails because both statements are true, not one.
• Option (d) fails because both statements are factually correct.

All three are among the classic evidences Wegener and his successors advanced for continental drift, and all three appear in the standard treatment in the NCERT physical geography text, giving (c).

• Statement I is the argument from rock and structural continuity: a belt of ancient rocks of comparable age and composition runs along the Brazilian coast and reappears on the coast of western Africa, which is difficult to explain unless the two margins were once joined.
• Statement II is the placer gold argument: the gold-bearing deposits of the Ghana coast lack a corresponding source rock nearby, while the Brazilian plateau supplies a plausible parent, implying juxtaposition of the two landmasses at the time of deposition.
• Statement III is the argument from the Gondwana sediments: the sequence found in peninsular India, characterised by tillite at its base indicating glaciation, has counterparts across Africa, Madagascar, Australia, Antarctica, the Falklands and South America, pointing to a single former supercontinent.
• Options (a), (b) and (d) each omit one of the three, and none of the statements contains an error that would justify its exclusion.

• Statement I is correct: polar motion, the wandering of the rotation axis relative to the crust, is measured continuously, and published work attributes a significant part of the recent drift, along with a lengthening of the day, to redistribution of mass at the surface.
• Statement II is correct as a standalone fact: solar flares and coronal mass ejections do deposit very large amounts of energy in the outermost atmosphere, heating and expanding the thermosphere, driving geomagnetic storms and increasing satellite drag.
• Statement III is correct: meltwater from the polar ice sheets does not stay at high latitudes but is redistributed through the oceans, with a net transfer of mass towards lower latitudes. The discriminating step is the explanatory link. Moving mass from the poles towards the equator increases the Earth's moment of inertia about the rotation axis and alters the mass distribution relative to that axis, which by conservation of angular momentum slows the rotation slightly and shifts the pole.
• Statement III therefore explains Statement I.
• Statement II does not: solar energy input affects the upper atmosphere and the magnetosphere, but is far too small and too external to move the rotation axis of a body of the Earth's mass. Both are correct, only one explains, giving (b).
• Option (a) wrongly admits the solar link, option (c) requires one statement to be false, and option (d) rejects both.

• Statement 1 is correct, since the western coast of the Peninsula is a faulted and submerged coast produced when a block west of the Western Ghats foundered along the Western Ghat fault, which is why that coast is narrow, has drowned river mouths and lacks a wide depositional plain, unlike the emergent eastern coast.
• Statement 2 is correct, because the Veliconda and Mahendragiri hills are discontinuous residual ranges of the Eastern Ghats, the worn down stumps of a very old orogeny, and residual relief is a defining mark of a stable ancient block.
• Statement 3 is incorrect and is the eliminator, since deep V shaped gorges cut by swift rivers are the signature of the young, still rising Himalaya, whose rivers have high vertical erosive power. Peninsular rivers flow over a block that has been stable for a very long time, have graded profiles close to base level and occupy broad shallow mature valleys, the Narmada and Tapi rift valleys being structural rather than erosional exceptions.

Hence 1 and 2 and (b) is correct, while (c) and (d) transfer a Himalayan characteristic to the Peninsula.