Geochronology

Geochronology is the science to determine the absolute age of rocks, fossils, and sediments, in a certain degree of uncertainty inherent in the methods used. Various types of age determination methods used by geologists to achieve this. 

Geochronology different application by biostratigraphy, which is the science of sedimentary rocks to put in a certain period geoogi through delineate, and benchmarking of Cataloging a collection of fossils of flora and fauna. Biostratigraphy not directly provide an absolute age determination of rocks, just place them in a given time interval in which the collection of these fossils have been known to have ever lived together. 

For example, with reference on the time scale of Geology, Permian and Over (Lopingian) lasted from 270.6 + / - 0.7 Ma to between approximately 250.1 + / - 0.4 Ma (Triassik oldest known) and 260.4 + / - 0.7 Ma (Lopingian youngest known) - a void in a collection of fossils that have determined its age, known to almost reach 10 Ma. While the biostratigraphic age of the Permian layers can show Lopingian, determining the actual age of these layers can be anywhere between 270 until 251 Ma. 

On the other hand, a determined old granite 259.5 + / - 0.5 Ma can reasonably called the "Permian", or more precisely, has mengintrusi in Permian time. 

Geochronology of science is the main tool used in the field Chronostratigraphy, which seeks to obtain absolute ages for all collection of fossils and determine the geologic history of Earth and the outer surface of the earth.