Radiocarbon dating is based on the fact that carbon-14 (an isotope of the extremely common element carbon) decays into another carbon isotope, carbon-12, at an exact rate.
Symbolically, the process of radioactive decay can be expressed by the following differential equation, where N is the quantity of decaying nuclei and k is a positive number called the exponential decay constant.
They've plotted rings from shipwreck timbers and roof beams, and wood from the Mediterranean, Russia, and China.
The bristlecone pine series, the longest built from a single species in a single location, stretches back to 7040... It is based on thousands of rings from 81 living trees and 118 dead trees, and Michael found more than three-quarters of the samples.
Other times, he had to fit together pieces of tree like a jigsaw puzzle.
According to Tom Gidwitz: "Dendrochronologists [scientists who study tree rings] have built sequences for a number of tree species, including German, Irish and Polish oaks, Patagonian cypresses, Lebanese cedars, pine, yew, spruce, and chestnut.
To rectify this, Michael Bird of the University of St.