Students not only want to know how old a fossil is, but they want to know how that age was determined.
Some very straightforward principles are used to determine the age of fossils.
The latest high-tech equipment permits reliable results to be obtained even with microscopic samples.
Radiometric dating is self-checking, because the data (after certain preliminary calculations are made) are fitted to a straight line (an "isochron") by means of standard linear regression methods of statistics.
This pattern of growth results in alternating bands of light-colored, low density "early wood" and dark, high density "late wood".
The slope of the line determines the date, and the closeness of fit is a measure of the statistical reliability of the resulting date.
Technical details on how these dates are calculated are given in Radiometric dating. As with any experimental procedure in any field of science, these measurements are subject to certain "glitches" and "anomalies," as noted in the literature.
Each dark band represents a winter; by counting rings it is possible to find the age of the tree (Figure 11.22).
The width of a series of growth rings can give clues to past climates and various disruptions such as forest fires.
Droughts and other variations in the climate make the tree grow slower or faster than normal, which shows up in the widths of the tree rings.