Radiometric dating clocks
After Charles Darwin's publication Origin of Species (Darwin himself was also a geologist) in 1859, geologists realised that particular fossils were restricted to particular layers of rock.
This built up the first generalised geological time scale.
The basic equation of radiometric dating requires that neither the parent nuclide nor the daughter product can enter or leave the material after its formation.
The possible confounding effects of contamination of parent and daughter isotopes have to be considered, as do the effects of any loss or gain of such isotopes since the sample was created.
The Geologic Time Scale was originally laid out using relative dating principles.
The geological time scale is based on the the geological rock record, which includes erosion, mountain building and other geological events.
Fossil assemblages 'fingerprint' formations, even though some species may range through several different formations.
This feature allowed William Smith (an engineer and surveyor who worked in the coal mines of England in the late 1700s) to order the fossils he started to collect in south-eastern England in 1793.
However, a more powerful tool was the fossilised remains of ancient animals and plants within the rock strata.However, the end of the Devonian was marked by the predominance of a different life form, plants, which in turn denotes the beginning of the Carboniferous Period.The different periods can be further subdivided (e.g.For example, decay of the parent isotope Rb-87 (Rubidium) produces a stable daughter isotope, Sr-87 (Strontium), while releasing a beta particle (an electron from the nucleus).("87" is the atomic mass number = protons neutrons.