Ring tree dating
A small core of the wood is removed and the rings are painstakingly counted.This remarkable tree was approximately 1400 years old, and grew on this rugged mountain ridge during the time of Mohammed.In this example, wood Sample D dates back to the year 1691.This represents an unbroken succession of 291 annual rings, almost three centuries of time recorded in four small pieces of wood.There is clearly a difference between the calcium content of wood during the wet and dry seasons that compares favorably with carbon isotope measurements. The calcium record can be determined in one afternoon at the synchrotron lab compared with four months in an isotope lab. This ancient juniper was approximately 1400 years old, and grew on this mountain ridge during the time of Mohammed.
The difference between wet and dry seasons for most trees is too subtle to make noticeable differences in the cell size and density between wet and dry seasonal growth. The 1906 ring pattern in wood Sample A (which was cut from Stump A) correlates with a 1906 ring pattern in Sample B which was cut from an older, undated Stump B. By matching up similar spaced rings in Samples B, C and D, the ages of ancient timbers can be determined.As long as the wood samples being compared have some ring patterns that coincide, time may be extended back through an unbroken succession of growth rings.Each year, most trees add an extra layer of growth to their trunks. As the tree gets older, the inside of the trunk looks like it is made up of a series of circles.
The center of these circles, or the absolute core of the tree, is known as the pith.
Since the rings are so close together, they must be counted under a dissecting microscope.