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The science of geochronology is the prime tool used in the discipline of chronostratigraphy, which attempts to derive absolute age dates for all fossil assemblages and determine the geologic history of the Earth and extraterrestrial bodies.By measuring the amount of radioactive decay of a radioactive isotope with a known half-life, geologists can establish the absolute age of the parent material.Each original isotope, called the parent, gradually decays to form a new isotope, called the daughter.Each isotope is identified with what is called a ‘mass number’.There are three main assumptions that must be made to accept radiometric dating methods.These must be accepted on faith in uniformitarian and naturalistic frameworks.By combining multiple geochronological (and biostratigraphic) indicators the precision of the recovered age can be improved.Geochronology is different in application from biostratigraphy, which is the science of assigning sedimentary rocks to a known geological period via describing, cataloguing and comparing fossil floral and faunal assemblages.
Even the use of isochron dating, which is supposed to eliminate some initial condition assumptions, produces dates that are not reliable.
When ‘parent’ uranium-238 decays, for example, it produces subatomic particles, energy and ‘daughter’ lead-206.
Isotopes are important to geologists because each radioactive element decays at a constant rate, which is unique to that element.
Biostratigraphy does not directly provide an absolute age determination of a rock, but merely places it within an interval of time at which that fossil assemblage is known to have coexisted.
Both disciplines work together hand in hand however, to the point where they share the same system of naming rock layers and the time spans utilized to classify layers within a stratum.