Which pair of elements can be used to determine the age of a fossil that is over one billion years old?

Potassium and Argon (⁴⁰K-⁴⁰Ar)

Explanation:

Potassium-Argon dating is a method used in geology and archeology to date rocks or volcanic ash, generally the oldest.

It is based on the principle of radioactive decay, it is a process that has a half-life of 1248 million years, during which time the gas is concentrated in the rock crystals. Taking advantage of this known rhythm and half-life, the method lends itself to dating samples ranging from 100.000 years to several billion years.

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