Dendrochronology dating techniques
Considering that the immediate post-Flood world would have been wetter with less contrasting seasons until the Ice Age waned (see Q&A: Ice Age), many extra growth rings would have been produced in the Bristlecone pines (even though extra rings are not produced today because of the seasonal extremes).
Dendrochronology, or tree-ring dating, provides absolute dates in two different ways: directly, and by calibrating radiocarbon results.
A tree's growth rate changes in a predictable pattern throughout the year in response to seasonal climate changes, resulting in visible growth rings.
During the first half of the 20th century, the astronomer A. Douglass founded the Laboratory of Tree-Ring Research at the University of Arizona.
In his Trattato della Pittura (Treatise on Painting), Leonardo da Vinci was the first person to mention that trees form rings annually and that their thickness is determined by the conditions under which they grew. S., Alexander Catlin Twining (1801–1884) suggested in 1833 that patterns among tree rings could be used to synchronize the dendrochronologies of various trees and thereby to reconstruct past climates across entire regions.
During the latter half of the nineteenth century, the scientific study of tree rings and the application of dendrochronology began.
See the cal BP discussion for additional information about radiocarbon calibration.
Example: analyzing ring widths of trees to determine how much rainfall fell per year long before weather records were kept.