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Samples of fossil coral and oolite from marine formations of the Bahamas and the Florida Keys have been analyzed for their concentrations of uranium and thorium isotopes. Ages calculated from the ratio Th(230): U(234) clearly indicate periods of marine limestone formation at about 85,000, 130,000, and 190,000 years ago, implying that the surface of the ocean was then close to its present level.
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Broecker et al. (1965) studied this question.
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