They proved this by showing that C-14 dates of wooden artifacts with cartouches (dated royal names) did not agree.

WASHINGTON — Researchers from Istituto Nazionale di Ottica (INO), within Consiglio Nazionale delle Ricerche (CNR), Italy have demonstrated a new compact spectroscopic instrument that offers a highly sensitive optical method for detecting radiocarbon dioxide concentration, which can be used to carbon date fossils and archaeological artifacts.

A new spectroscopic technique offers ultra-sensitive optical detection of radiocarbon dioxide.

The approach shows promise as a measurement tool in many fields, including carbon dating and greenhouse gas detection.

That methodology has been refined and improved several times over the last few years. The date was chosen because radiocarbon dating was invented in the late 1940s.Most importantly, researchers discovered that radiocarbon dates are affected by the amount of carbon in the atmosphere, which has fluctuated greatly in the past for both natural and human-caused reasons (such as the invention of iron smelting, the Industrial Revolution and the invention of the combustion engine). The problem is, of course, that CE and BCE still use the putative date of the birth of Christ as the reference points for its numbering system: the two years 1 BCE, 1 CE are equivalent to 1 BC, 1 AD.Tree rings, which record the amount of atmospheric carbon in their rings, are used to calibrate radiocarbon dates. However, a major disadvantage with using BP is--the present year, of course, changes every twelve months.Other isotopes are used by geologists to date older material.Each radiocarbon date has a statistical probability shown by the ± number.