Isotopic dating of rocks, or the minerals in them, is based on the fact that we know the decay rates of isotope used for dating fossils unstable isotopes of elements and that these rates have been constant over geological time. One of the isotope pairs widely used in geology is the decay of 40K to 40Ar potassium to argon It has a half-life of 1. Feldspar does not have any argon in it when it forms.
Argon is a gas and the atoms of 40Ar remain embedded within the crystal, unless the rock is subjected to high temperatures after it forms. The sample must be analyzed using a very sensitive mass-spectrometer, which can detect the differences between the masses of atoms, and can therefore distinguish between 40K and the much more abundant 39K.
Biotite and hornblende are also commonly used for K-Ar isotope used for dating fossils. An important assumption that we have to be able to make when using isotopic dating is that when the rock formed none of the daughter isotope was present e. 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.
Furthermore, in almost all cases, the fragments have come from a range of source rocks that all formed at different times.
Absolute dating is the process of determining an age on a specified chronology in archaeology For example, techniques based on isotopes with half lives in the thousands of years, such as One of the most widely used and well-known absolute dating techniques is "Amino Acid Racemization Dating of Fossil Bones". Radioisotope dating cannot be used directly on fossils since they don't contain the unstable radioactive isotopes used in the dating process. To determine a.