Finding the age of a tree by counting annual growth rings is called dendrochronology. Each growth ring has a lighter portion (springwood) and a darker bit (summerwood). This is a chunk of wood I came across on a beach walk a few years ago. One of my favorite natural concentric ring formations.
Taken on Restoration Point, Bainbridge Island WA
Camera: WA With a Canon EOS Rebel T1i
Lens: 18-55mm f/3.5-5.6 IS