Dating by radioisotopes
Without absolute ages, investigators could only determine which fossil organisms lived at the same time and the relative order of their appearance in the correlated sedimentary rock record.
Unlike ages derived from fossils, which occur only in sedimentary rocks, absolute ages are obtained from minerals that grow as liquid rock bodies cool at or below the surface.
The technique of comparing the abundance ratio of a radioactive isotope to a reference isotope to determine the age of a material is called radioactive dating.
Many isotopes have been studied, probing a wide range of time scales.
To date past events, processes, formations, and fossil organisms, geologists employ a variety of techniques.
In the ideal case, the geologist will discover a single rock unit with a unique collection of easily observed attributes called a marker horizon that can be found at widely spaced localities.
Any feature, including colour variations, textures, fossil content, mineralogy, or any unusual combinations of these can be used.
The man's body was recovered and pieces of tissue were studied for their C content by accelerator mass spectroscopy.
The best estimate from this dating technique says the man lived between 33 BC. From the ratio, the time since the formation of the rock can be calculated.