How paleontologists estimate geologic time through radiometric dating

This technique uses the same minerals and rocks as for K-Ar dating but restricts measurements to the argon isotopic system which is not so affected by metamorphic and alteration events. The decay of 147Sm to 143Nd for dating rocks began in the mid-1970s and was widespread by the early 1980s.It is useful for dating very old igneous and metamorphic rocks and also meteorites and other cosmic fragments.The amount of 14C present and the known rate of decay of 14C and the equilibrium value gives the length of time elapsed since the death of the organism.

Others place mineral grains under a special microscope, firing a laser beam at the grains which ionises the mineral and releases the isotopes.

All living organisms take up carbon from their environment including a small proportion of the radioactive isotope 14C (formed from nitrogen-14 as a result of cosmic ray bombardment).

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