Question

Why does the C-14/C-12 ratio change with time in fossils?

Answer 1

Answer:

C. C-14 decays but C-12 stays the same after death.

Explanation:

C-12 is stable and won't change.  C-14 is slightly radioactive.  It decays over time to C12.  A living plant or animal has a fairly constant C14/C12 ratio during it's lifetime.  Sources of food have a fairly consistent C-14/C-12 ratio.  Once it dies, the C-14 is no longer replenished, so the ratio of C-14 to C-12 drops over time, giving paleontologists the ability to carbon-date the sample.  The less C-14, the older the sample.