A recent paper in Nature shows how quantitative improvements in scientific instruments can bring broad new vistas to light. Carbon 14 dating was devised to date carbon in organic matter, from bones to charcoal, in archaeology, but carbon 14 forms in any material containing nitrogen that is exposed at the Earth’s surface to the neutrons generated by cosmic rays.
The quantitative problem of applying the C14 technique to materials containing mere traces of nitrogen and carbon, like quartz , has been solved in recent years by advances in accelerator mass spectrometry, which allows dates to be calculated even if only a few parts per million of carbon are present.
The Nature paper reports on the exposure of rocks on
The top of a granite Obelisk like 'Cleopatra's Needle', for example ,might yield a quartz 14 C age of 3500 while the bottom, reflecting its having been toppled in say, 500 AD might yield one of 1500