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A system to date the age of rocks.

The samarium-neodymium system is a relative newcomer to the field of geochronology.

Similar to the Potassium-argon dating method, this method measures the ratio of samarium which has decayed into neodymium. Very precise measurements are necessary, since the half-life of samarium-147 is around 106000000000 years.

This also means that during the time since the Earth formed, only around 3% of the samarium-147 originally present has decayed into neodymium-143.