As the good fellow mentioned in the video above, the science of studying history through tree rings is called "dendrochronology". It's a fascinating field of study that allows scientists to investigate a whole range of things based on the tree ring data provided by wood from living or dead trees, lumber from ships or structures, or even panels on which old paintings were made.
Here is a nice video of a team of scientists working in the Rocky Mountains of Montana to collect and analyze tree ring data to add to our growing knowledge of climate variation. It has some excellent detail of the tree boring and ring measurement processes. As you know if you've ever counted tree rings, it can get a little tricky, and these folks have really got the process "down to a science."
Tree ring counting in the Rocky Mountains...a great job if you can get it.