There is a whole field of science devoted to the invention and development of dating methods—or “clocks” as we may think of them. It is called geochronology, the science of dating events. There are relatively few geochronologists, scientists trained in the use of all kinds of dating methods and in the theories upon which these methods are based.

Geochronologists tell us that there are two major types of clocks: those that tick at an absolute rate of speed which can be measured, and those which tick only once in a while. A clock of the first type yields what is called an absolute date, revealing the number of hours, days, years, centuries or millennia since an event occurred. A clock of the second type yields what is called a relative date, placing an event as before or after another event, but does not tell us exactly how far they are apart in time nor how long ago they occurred.

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