Methuselah's tree ring sequence near its core -- when it was a young tree -- was matched to the sequence found in pieces of nearby trees which had died previously. Henry Michael of the University of Pennsylvania's Museum Applied Science Center for Archaeology (MASCA) scanned the area almost every summer for over three decades.His goal was to find sections of dead trees whose rings could be pieced together to extend the samples as far back in time as possible.The technique hinges on carbon-14, a radioactive isotope of the element that, unlike other more stable forms of carbon, decays away at a steady rate.

Various geologic, atmospheric and solar processes can influence atmospheric carbon-14 levels.

Since the 1960s, scientists have started accounting for the variations by calibrating the clock against the known ages of tree rings.

The method was developed by Willard Libby in the late 1940s and soon became a standard tool for archaeologists.

Libby received the Nobel Prize in Chemistry for his work in 1960.

Other corrections must be made to account for the proportion of throughout the biosphere (reservoir effects).

Additional complications come from the burning of fossil fuels such as coal and oil, and from the above-ground nuclear tests done in the 1950s and 1960s.

Samples from the tree were able to generate calibration points back to that date. It is narrow or broad, depending upon whether the weather during that year was dry or wet, and whether the tree was exposed to various stressors.

Bristlecone pines grow so slowly that its rings are paper thin; their width has to be studied under a microscope.

There are two techniques for dating in archaeological sites: relative and absolute dating.