Below is an example of two core samples that have been matched according to the characteristic growth patterns recorded in the rings of trees from the same region. Working backwards from live trees (where the outermost ring corresponds with the present year) dendrochronologists match dated ring patterns to progressively older and older samples, reconstructing the past as they go.

With the help of image processing applications, tree ring scientists are revealing much more than just the date. Optical density analysis is now being used to collect information on weather conditions from hundreds of years ago.

Stay tuned for your weather forecast (pre-cast ?) from 532 A.D.!

For more information on the science of tree ring crossdating, check out the Laboratory of Tree Ring Research web site at:
http://tree.ltrr.arizona.edu/~sheppard/SkeletonPlot/frames.htm