In many cases, the daughter nuclide itself is radioactive, resulting in a decay chaineventually ending with the formation of a stable nonradioactive daughter nuclide; each step in such a chain is characterized by a distinct half-life. Because, the unknown fossil, the red sponge, was found with the fossils in fossil assemblage B it also must have existed during the interval of time indicated by the red box. In these cases, the half-life of interest in radiometric dating is usually the longest one in the chain. On the other hand, the concentration of carbon falls off so steeply that the age of relatively young remains can be determined precisely to within a few decades. For dates up to a few million years micastektites glass fragments from volcanic eruptionsand meteorites are best used. A clastic sedimentary rock is made up of older rock and mineral fragments, and when the rock forms it is almost certain that all of the fragments already have daughter isotopes in them. Just as when they were deposited, the strata are mostly horizontal principle of original horizontality.
Principles and applications of geochemistry:
Radiometric Age Dating
It might be possible to date some chemical sedimentary rocks isotopically, but there are no useful isotopes that can be used on old chemical sedimentary rocks. For instance, carbon has a half-life of 5, years. The direction of the earth's magnetic field, which can be normal polarity or reversed polarity.