Assertion (A) : Rich placer deposits of gold are found on the Ghana coast and gold-bearing veins are found in Brazil. Reason (R) : At some points of time, these continents were joined together along the Atlantic coast.
Select the correct answer.

Question

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Correct — A, Both A and R are true and R is the correct explanation of A. The stem is lifted almost word for word from NCERT Class XI, Fundamentals of Physical Geography, Chapter 4, where the placer-deposit evidence for continental drift reads in full: 'The occurrence of rich placer deposits of gold in the Ghana coast and the absolute absence of source rock in the region is an amazing fact. The gold bearing veins are in Brazil and it is obvious that the gold deposits of the Ghana are derived from the Brazil plateau when the two continents lay side by side.' The examiner has simply cut that sentence in two and labelled the halves A and R, so both halves of the assertion are true as the standard text states them. The reason is true as well: Africa and South America were both part of Gondwanaland, the southern component of the supercontinent Pangaea, which the same chapter says began to split about 200 million years ago. What decides between (a) and (b) is whether the reason does explanatory work, and here it does all of it. Placer gold is, by definition, gold that has been weathered out of a source rock and re-concentrated by moving water, so a rich placer with no source rock behind it is not a curiosity but a contradiction — the metal has to have come from somewhere. The chapter's answer is that the somewhere is the vein country of the Brazilian plateau, which lay against the Ghana coast before an ocean opened between them. Take the joined-continents fact away and the assertion has no explanation at all; put it back and the anomaly dissolves. That is exactly the relationship option (a) describes. The paragraph immediately before it in the same chapter supplies an independent check on the same pairing: 'The belt of ancient rocks of 2,000 million years from Brazil coast matches with those from western Africa. The earliest marine deposits along the coastline of South America and Africa are of the Jurassic age.' Those two-billion-year-old rocks are the same Palaeoproterozoic province that carries West Africa's gold, so the drift explanation for the gold is not an isolated assertion but a special case of a match already established on rock ages — which is why the textbook, and UPSC after it, treat it as evidence rather than coincidence.

Why the other options are wrong — (b) The most tempting wrong option, and the one that catches candidates who read the assertion as two separate observations sitting side by side rather than as one puzzle. Choosing (b) means claiming that the joined continents are a true fact which happens to be irrelevant to Ghana's placer gold — but the assertion is not 'Ghana has gold and Brazil has gold'. It is that Ghana's gold arrived without a local source while the veins that could have supplied it lie across an ocean, and the only thing that closes that gap is the former adjacency. In an assertion–reason item, ask what work the reason is doing: if deleting R leaves A unexplained, R is the explanation. Here deleting R leaves A as an unexplained anomaly, which is precisely why the textbook lists it under evidence for continental drift.  (c) Both halves of A are stated as fact in the standard text — rich placer gold on the Ghana coast, gold-bearing veins in Brazil — and both are independently true of the real world. The Gold Coast took its European name from the metal, is estimated to have supplied about two-thirds of Africa's gold production between the late fifteenth and the mid-nineteenth century, and has yielded on the order of 1,500 tonnes of gold across its history; Brazil's plateau gold sustained a colonial gold rush of its own. Nothing in A is denied by anyone. A candidate reaches this option only by assuming the observation must be wrong because the conclusion sounds improbable, which inverts the logic of an assertion–reason item — you test the statements first and the explanation second, never the other way round.  (d) This is the trap for a half-remembered fact: that Wegener's theory was 'rejected'. What his contemporaries rejected was his proposed mechanism — the pole-fleeing force arising from the earth's equatorial bulge and the tidal force of the moon and sun — which NCERT records 'most of scholars considered … to be totally inadequate'. The drift itself was never falsified. Arthur Holmes offered mantle convection currents in the 1930s, post-war mapping of the ocean floor produced Hess's sea-floor spreading in 1961, and McKenzie and Parker, and independently Morgan, assembled plate tectonics in 1967, which absorbed drift as one of its consequences. So the mechanism changed and the claim survived: Africa and South America really were joined, and R is true.

Concept: Alfred Wegener, a German meteorologist, set out the continental drift theory in 1912, though Abraham Ortelius had noticed the Atlantic fit as early as 1596 and Antonio Pellegrini had drawn the three continents together. Wegener held that all land once formed a single mass, Pangaea — 'all earth' — surrounded by a single ocean, Panthalassa, and that about 200 million years ago Pangaea split into Laurasia in the north and Gondwanaland in the south, which broke up further into today's continents. He offered five main lines of evidence, and it is worth knowing them as a set because examiners draw from all five: the jig-saw fit of the Atlantic coasts, confirmed by Bullard's computer best-fit in 1964; rocks of the same age across the ocean; glacial tillite at the base of the Gondwana sequence; placer deposits; and the distribution of fossils. This question tests the fourth. Note what kind of evidence it is. It is not a resemblance between two shapes, which could be coincidence, but a mismatch between a mineral and its surroundings — an effect with no available cause — which only makes sense if the cause has since moved away. Evidence of that form is much harder to explain away than a coastline that happens to fit.

State PCS 2023 Q91 — Geography PYQ with Answer

State PCS 2023 Q91 — Geography PYQ with Answer