In 1837, Charles Darwin presented a paper to the British Geological Society arguing that coral atolls were formed not on submerged volcanic craters, as argued by pioneering geologist Charles Lyell, but on the subsidence of mountain chains.

The problem, as Darwin saw it, was that corals can not live more than about 30 feet below the surface and therefore they could not have formed of themselves from the ocean floor. They needed a raised platform to build upon.

Charles Darwin as a young man

However, the volcanic crater hypothesis didn’t satisfy Darwin; he thought the atoll shape was too regular to have been the craters of old volcanos. There were no atoll formations on land, Darwin reasoned; why would there be such in the ocean? Therefore, Darwin proposed that corals were building upon eroded mountains, an hypothesis that, he wrote happily, “solves every difficulty.”

Darwin also argued, in 1839, that curious geological formations—what appeared to be parallel tracks—in the Glen Roy valley of Scotland were the result of an uplifted sea bed.

Darwin didn’t have any actual physical evidence to support these two hypotheses: he arrived at them deductively, through the principle of exclusion. A deductive conclusion is reached through theory—if X, then logically Y must be so—as opposed to induction, which builds a theory out of empirical data. The principle of exclusion works from the premise that “there is no other way of accounting for the phenomenon.”[1] Continue Reading »