I can add little to this excellent piece. however variable growth rate may be, total height divided by maximum growth rate gives a *lower limit* the age, which is enough to refute the Young Earth creationist. There was at one time hope that fine structure of coral growth bands would give information about the lengths of the day and the month in the Proterozoic, but because laboratory studies showed these structures to be sensitive to accidents of time and tide, their place has now been taken by rhythmites, variations in the fine structure of the annual banding of sediments (Proterozoic and Precambrian day and month lengths are now studied using rhythmites, fine structure in the annual banding of sediments; Williams, Reviews of Geophysics 38, 1, 2000). 234U-230Th dating is one of the best methods available for carbonate rocks in the 10,000 year range, and the creationist claim that decay rates could have been different in the past ignores the fact, known since 1928, that these rates are the inevitable consequence of time-dependent quantum mechanics and the fundamental constants of nature.
Corals are among the most valuable indicators of past climate conditions, due to their sensitivity to water depth, temperature, and acidity. We can infer from the age and depth of ancient reefs, for example, how global sea level has varied in response to past intervals of warming and cooling. Since reefs are formed by organisms secreting calcite, moreover, their isotopic and elemental chemistry is directly related to the temperature and salinity of the water in which they lived. But best of all, reefs form in the tropics (30°S – 30°N), which means that the researchers studying them do so while scuba diving in warm seas along pristine beaches. Perhaps it’s time for a career change?
Despite that corals can provide a wealth of information to geologists and climatologists studying the past, these data are useful only if we know the precise age of the sample! How then do we date…
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