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This technique is good for iron meteorites and the mineral molybdenite.

This system is highly favoured for accurate dating of igneous and metamorphic rocks, through many different techniques.

Radiocarbon dating is normally suitable for organic materials less than 50 000 years old because beyond that time the amount of 14C becomes too small to be accurately measured.

This scheme was developed in 1937 but became more useful when mass spectrometers were improved in the late 1950s and early 1960s.

The Re-Os isotopic system was first developed in the early 1960s, but recently has been improved for accurate age determinations.

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The amount of carbon isotopes within living organisms reaches an equilibrium value, on death no more is taken up, and the 14C present starts to decay at a known rate.

The relationship between the two is: T = 0.693 / λ Many different radioactive isotopes and techniques are used for dating.

All rely on the fact that certain elements (particularly uranium and potassium) contain a number of different isotopes whose half-life is exactly known and therefore the relative concentrations of these isotopes within a rock or mineral can measure the age.

However, potassium is very mobile during metamorphism and alteration, and so this technique is not used much for old rocks, but is useful for rocks of the Mesozoic and Cenozoic Eras, particularly unaltered igneous rocks.

Argon-Argon dating (39Ar-40Ar) This technique developed in the late 1960s but came into vogue in the early 1980s, through step-wise release of the isotopes.

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