Project co-leader Neil Pederson of Lamont-Doherty Earth Observatory takes cross-sections of ancient trees. (Kevin Krajick / Earth Institute)
Rings are clearly visible in well-preserved tree specimens. Taken back to the lab, polished, and inspected under a microscope, they can be dated to the year. (Kevin Krajick / Earth Institute)
Living trees are harmlessly sampled using a corkscrew-like tool that extracts a straw-size core. (Kevin Krajick / Earth Institute)
