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The methods that are used depend on the presumed age of the site from which they were excavated.For instance, if a site is believed to be over 100,000 years old, dendrochronology and radiocarbon dating could not be used.

This does not mean that radiometric dates or any other scientific measurements are unreliable.billion years, the chronometric age of a sample can be calculated.This dating method can be used with samples that are as young as a few decades to as old as the earth and beyond.In the example below, the bone must date to sometime between 1.75 and 1.5 million years ago.For instance, a date of 100,000 5,000 years ago means that there is a high probability the date is in the range of 95,000 and 105,000 years ago and most likely is around 100,000.Fossils are generally found in sedimentary rock — not igneous rock.

Sedimentary rocks can be dated using radioactive carbon, but because carbon decays relatively quickly, this only works for rocks younger than about 50 thousand years.It is also based on the fact that background radiation causes electrons to dislodge from their normal positions in atoms and become trapped in the crystalline lattice of the material.When odd numbers of electrons are separated, there is a measurable change in the magnetic field (or spin) of the atoms.The atoms of crystalline solids, such as pottery and rock, can be altered by this radiation.Specifically, the electrons of quartz, feldspar, diamond, or calcite crystals can become displaced from their normal positions in atoms and trapped in imperfections in the crystal lattice of the clay molecules.As a result, there is a changing ratio of carbon-14 to the more atomically stable carbon-12 involves actually counting individual carbon-14 atoms.