Consider the following pairs:

Question

Consider the following pairs:

Theory Proponent

The correct match is:

1. A. 1-i, 2-iii, 3-ii, 4-iv
2. B. 1-iii, 2-ii, 3-iv, 4-i
3. C. 1-ii, 2-i, 3-iii, 4-iv
4. D. 1-i, 2-iii, 3-iv, 4-ii (Correct answer)

Correct Answer

Option D — 1-i, 2-iii, 3-iv, 4-ii

Detailed Solution & Explanation

The correct answer is 1-i, 2-iii, 3-iv, 4-ii.

Key Points

• Matching each theory of coral reef formation with its proponent:

• This gives 1-i, 2-iii, 3-iv, 4-ii.

Additional Information

• Darwin's Subsidence Theory (1842) is the classic account. As a volcanic island slowly subsides, the coral colony fringing it keeps growing upward to stay in shallow, sunlit water. The fringing reef becomes a barrier reef as the lagoon widens, and when the island finally disappears beneath the surface an atoll remains. It elegantly explains why atolls occur over volcanic chains.
• Murray's Standstill (Stationary) Theory rejected subsidence, holding that reefs grow on pre-existing submarine platforms — shoals and banks built up by sediment — that rise close enough to the surface for coral to colonise, with no crustal movement required.
• Daly's Glacial Control Theory (1910) invoked the Pleistocene ice ages: sea level fell by 100 metres or more, and wave action planed off islands to create flat platforms. As the ice melted and sea level rose, corals grew upward on these platforms, keeping pace with the rise.
• Conditions corals need: water temperature roughly 20–30 °C, depth under about 50 metres for sunlight to reach the symbiotic zooxanthellae, normal salinity, clear sediment-free water, and a firm substrate. This confines reefs to shallow tropical seas between about 30° N and 30° S, and explains their absence off river mouths carrying silt and fresh water.
• Coral bleaching occurs when heat stress causes corals to expel their zooxanthellae, losing both colour and their main energy source. India's major reef areas are the Gulf of Mannar, Gulf of Kachchh, Lakshadweep and the Andaman & Nicobar Islands.