Other critics, perhaps more familiar with the data, question certain aspects of the quality of the fossil record and of its dating.
A relative age is the age of a fossil organism, rock, or geologic feature or event defined relative to other organisms, rocks, or features or events rather than in terms of years.
A portion of the carbon is the radioactive isotope carbon-14.
At death, the exchange stops, and the carbon-14 then decays with a known half-life, which enables scientists to calculate the time of death.
Tradition paleontological and biostratigraphic correlation methods are still perhaps the most common relative dating methods used by geologists.
More modern correlation technologies include use of marine stable isotope records, paleomagnetic dating, tephrachronology, geomorphological methods, sedimentation characteristics, and other geochemical and radiometric methods.Geologic assessment of active tectonism depends on two key measures: the age and the amount of deformation of a given stratigraphic unit.