A radioactive isotope used for geological dating has half-life 1.25×10⁹ years. A mineral currently contains 25% of the parent isotope that it contained when the mineral formed, and the system has remained closed. The age of the mineral is:
Options

Question

A radioactive isotope used for geological dating has half-life 1.25×10⁹ years. A mineral currently contains 25% of the parent isotope that it contained when the mineral formed, and the system has remained closed. The age of the mineral is:

Options

G1 Physics · Accepted Answer

A remaining fraction of 25% means N ÷ N₀ = 0.25 = 1 ÷ 4 = 1 ÷ 2². Therefore two half-lives have elapsed. Age = 2×1.25×10⁹ = 2.50×10⁹ years. Correct option: B.