And radiocarbon dating
This can be overcome by calibration curves calculated by dating materials of precisely known age. The best samples are tree rings, but annually laminated sediments have also produced excellent results. Chudy, Eristavi, Pagva, Povinec, Sivo, and Togonidze. Anthropogenic 14C variations in atmospheric CO2 and wines. One site, many major programs: CALIB, Marine Reservoir Correction, CALIBomb, Int Cal13, SHCal13, Int Cal09. This is an online radiocarbon calibration program with downloadable versions for Windows and Mac platforms. Arizona AMS lab https://ams.arizona.edu/radiocarbon GNS Science AMS lab https:// Arizona Tree Ring Lab leave a comment at the bottom of the page to report errors or suggest links.) CALIB Home Page.Since the carbon in these fuels was ancient, it contained no radiocarbon. Therefore, prior to atmospheric bomb testing, the proportion of radiocarbon to C was relatively low, giving relatively old ages. Nitrogen atoms high in the atmosphere can be converted to radiocarbon if they are struck by neutrons produced by cosmic ray bombardment.
The ocean circulates high quantities of ancient carbon deep in the ocean. Therefore, radiocarbon dates are calculated to a "pre-bomb" age of 1950 A. Material which died after 1950 has such high amounts of radiocarbon its age is reported as "percent modern (1950)" (example 180% modern).