Question

what would the percentage of thorium-232 ( parent compound) be in a rock that was dated at 1.8 billion years

Answer 1

The half-life of Th-232 is 1.405 × 10¹⁰ years

Time elapsed = 2.8 x 10⁹ years

Equation of radioactive decay:

A = A₀ = (1/2)^ t/t₁/₂

Thus, the percentage of thorium-232 in the rock that was dated at 2.8 billions year = 87.1%