Scientists use the decay of potassium-40 to argon-40 to determine the age of rock. The potassium-40 decay has a half-life of 1.3 x 10⁹ years.

Which rock is older, rock 1 with a mass ratio (argon-40 to potassium-40) of 0.5, or rock 2 with a mass ratio of 3.47?
A. Rock 1
B. Rock 2