Radiometric dating of ordovician period
The principle of radiocarbon dating is simple: the rates at which various radioactive elements decay are known, and the ratio of the radioactive element to its decay products shows how long the radioactive element has existed in the rock.This rate is represented by the half-life, which is the time it takes for half of a sample to decay.
Stratigraphy is the science of understanding the strata, or layers, that form the sedimentary record.
This is difficult for some time periods, however, because of the barriers involved in matching rocks of the same age across continents.
Family-tree relationships can help to narrow down the date when lineages first appeared.
However, these “molecular clocks” are sometimes inaccurate and provide only approximate timing.
For example, they are not sufficiently precise and reliable for estimating when the groups that feature in the Cambrian explosion first evolved, and estimates produced by different approaches to this method may vary as well.
Radioactive elements are common only in rocks with a volcanic origin, so the only fossil-bearing rocks that can be dated radiometrically are volcanic ash layers.