It is therefore essential to have as much information as possible about the material being dated and to check for possible signs of alteration. Precision is enhanced if measurements are taken on multiple samples from different locations of the rock body.
Alternatively, if several different minerals can be dated from the same sample and are assumed to be formed by the same event and were in equilibrium with the reservoir when they formed, they should form an isochron. In uranium-lead dating, the concordia diagram is used which also decreases the problem of nuclide loss.
Divisions in the geological time scales still use fossil evidence and mark major changes in the dominance of particular life forms.
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.
On the other hand, the concentration of carbon-14 falls off so steeply that the age of relatively young remains can be determined precisely to within a few decades.
Numerical dating takes advantage of the "clocks in rocks" - radioactive isotopes ("parents") that spontaneously decay to form new isotopes ("daughters") while releasing energy.
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.Finally, correlation between different isotopic dating methods may be required to confirm the age of a sample.For example, the age of the Amitsoq gneisses from western Greenland was determined to be 3.6 ± 0.05 million years ago (MA) using uranium-lead dating and 3.56 ± 0.10 Ma using lead-lead dating, results that are consistent with each other.For instance, carbon-14 has a half-life of 5,730 years.After an organism has been dead for 60,000 years, so little carbon-14 is left that accurate dating can not be established.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).