Model Half-Life in Rock Dating

5 questions0m 0s

Learn the skill

After one half-life, half the original parent isotope remains; after two, one quarter remains. Geological dating also requires knowing what event a mineral records and whether the isotope system stayed closed.

Worked example

For an invented isotope with a 3-million-year half-life, 25% parent remaining corresponds to two half-lives, or 6 million years, if the model's assumptions hold.

1. What percentage of the original parent remains after one half-life? Answer

2. What percentage remains after two half-lives? Answer

3. If the half-life is 2 million years, how many million years correspond to 12.5% parent remaining? Answer

4. Why can gaining or losing isotopes after formation cause problems? It makes all minerals identical It can violate the closed-system assumption It changes every half-life to one day

5. Does a mineral's date automatically equal the age of any sedimentary rock containing it? Yes, all grains form during deposition Yes, every rock has one identical history No, a grain can be older than the sediment that contains it