Assume that a particular radioactive-isotope dating method has a half-life of 150 million years. Also assume that the parent isotope is commonly incorporated in igneous-rock minerals but that the daughter isotope is not
Measurements show that one crystal in an igneous rock contains 5 million atoms of the parent isotope and 75 million atoms of the daughter isotope. How old is this crystal?
What will be an ideal response?
5 million parent isotope + 75 million of the daughter isotope = 80 million parent isotope as the clock starts
Parent Daughter Half-lives
80 million 0 0
40 million 40 million 1
20 million 60 million 2
10 million 70 million 3
5 million 75 million 4
4 half-lives have gone by. If each half-life takes 150 million years, then the age of the crystal is 600 million years old (150 million years/half-life x 4 half-lives = 600 million years old).
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