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Geography Optional 300+ Score Pack · Model answer

Compare the Subsidence and Glacial control theories on the formation of coral reefs.

  • UPSC 2013
  • Oceanography

Both theories answer the coral reef problem: reef-building corals grow only in warm (optimum about 23–29°C), clear, sunlit water of near-normal salinity, mostly within a few tens of metres of the surface — yet barrier reefs and atolls stand on reef limestone hundreds of metres thick and enclose lagoons of fairly even depth.

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What the full answer covers

  • Darwin's Subsidence Theory
  • Daly's Glacial Control Theory
  • Point-by-Point Comparison
  • Testing the Theories — Drilling and Later Work

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