These ages have been derived from relative dating and absolute dating (radiometric dating) of rock layers and fossils.
(a) Relative Dating This technique uses principles of stratigraphy (rock strata) and the study of fossils (palaeontology) to determine the relative ages of rocks and sediments. Field geologists' rely on a number of simple techniques for dating rocks and constructing geological successions. The Law of Strata Identified by Fossils is a little bit more complex.
Since certain species of animals existed on Earth at specific times in history, the fossils or remains of such animals embedded within those successive layers of rock also help scientists determine the age of the layers.
Similarly, pollen grains released by seed-bearing plants became fossilized in rock layers.
The table below summarises key features: Gastrioceras listeri is a particularly good example of a ZONE fossil.
Archaeologists have access to various techniques for dating archaeological sites or the objects found on those sites.
When museums and collectors purchase archaeological items for their collections they enter an expensive and potentially deceptive commercial fine arts arena.
Healthy profits are to be made from illicitly plundered ancient sites or selling skillfully made forgeries.
Instead, other methods are used to work out a fossil’s age.
These include radiometric dating of volcanic layers above or below the fossils or by comparisons to similar rocks and fossils of known ages.