DarwinsTheory

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Darwin's Theory

Darwin grouped coral reefs into three distinct types: barrier, fringing, and atolls. He believed that each reef type was really a separate stage of reef development around a slowly sinking volcanic island.[1]

[2]

Stage 1 - Fringing Reef

A submarine volcano forms an island rising from the sea floor. Corals begin to grow in the shallow regions off the coast of the island. As the island gradually sinks, the reef grows upward in order to stay within a sunlit range. A fringing reef is a reef encircling this volcanic island while it first begins to sink.[3]

Stage 2 - Barrier Reef

As the volcanic island continues to sink, a lagoon begins to form between the reef and the exposed island. In this phase, the reef is a barrier reef.[4]

Stage 3 - Atoll

Once the volcanic island is fully submerged, the reef is known as an atoll. The reef outline is circular with a central lagoon.[5]

Evidence

The Deep Sea Drilling Project sought evidence of volcanic cores beneath coral reefs and found it. First, in 1952 at the Einwetok Atoll in the Marshall islands, and again, in 1960 at the Midway Atoll, teams found volcanic rock strongly supporting Darwin's theory that coral reefs form around submerging islands. However, not all coral reefs have similar evidence, meaning Darwin outlined one way reefs form, not the only way.[6]


Notes

  1. Strykowski and Bonem, p. 18-19
  2. Strykowski and Bonem, p. 19
  3. Strykowski and Bonem, p. 19
  4. Strykowski and Bonem, p. 19-20
  5. Strykowski and Bonem, p. 20
  6. Strykowski and Bonem, p. 20

References

  • Strykowski, Joe and Rena M. Bonem. Palaces Under the Sea. Crystal River, FL: Star Thrower Foundation, 1993, p. 19-26. Print.
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