The isotope 232Th decays to 208Pb by the emission of six alpha particles, with a halflife of 1.39 × 1010 years. Analysis of 1.00 kg of ocean sediment shows it to contain 7.4 mg of 232Th and 4.9 × 10^-3 cm3 of gaseous helium at 0°C and atmospheric pressure. Estimate the age of the sediment, assuming no loss or gain of thorium or helium from the sediment since its formation and assuming that the helium arose entirely from the decay of thorium.

The isotope 232Th decays to 208Pb by the emission of six alpha particles, with a halflife of 1.39 × 1010 years. Analysis of 1.00 kg of ocean sediment shows it to contain 7.4 mg of 232Th and 4.9 × 10^-3 cm3 of gaseous helium at 0°C and atmospheric pressure. Estimate the age of the sediment, assuming no loss or gain of thorium or helium from the sediment since its formation and assuming that the helium arose entirely from the decay of thorium.

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