Question

Rock Layer E is 250,000 years old. Rock Layer C is 200,000 years old. Rock layer C has not undergone radioactive decay and has 18 radioactive isotopes. The half-life is 50,000 years. Rock Layer E has undergone radioactive decay ONCE, how many daughter and parent isotopes are present in layer E?

Answer 1

Step-by-step explanation:

Rock Layer E is 250,000 years old. Rock Layer C is 200,000 years old. So the two layers are off by 50,000 years; equal to one half-life.

As Rock Layer E has undergone radioactive decay ONCE, each parent isotope forms one daughter isotope after the decay.

Rock layer C has not undergone radioactive decay and has 18 radioactive isotopes. So that represents an equal number of parent and daughter isotopes, i.e. 9 parent and 9 daughter isotopes.

So there are 9 parent and 0 daughter isotopes in layer E.

Answer 2

Step-by-step explanation:

By definition, after a radio active decay, a parent isotope will create a daughter isotope.

Layer C is exactly one half-life from Layer E at 50000 years. So half of the original parent isotopes from Layer E would have decayed to form daughter isotopes. As C has 18 radioactive isotopes together, E should have 6 daughter and 6 parent isotopes.