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

A. C-14 is no longer being produced in the atmosphere.
B. The C-14 half-life changes over time in a known way.
C. C-14 decays but C-12 stays the same after death.
D. C-12 also begins to decay over long periods of time.

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.

Why does the C-14/C-12 ratio change with time in fossils? A. C-14 is no longer being produced in the atmosphere. B. The C-14 half-life changes over time in a known way. C. C-14 decays but C-12 stays the same after death. D. C-12 also begins to decay over long periods of time. ​

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

A. C-14 is no longer being produced in the atmosphere.
B. The C-14 half-life changes over time in a known way.
C. C-14 decays but C-12 stays the same after death.
D. C-12 also begins to decay over long periods of time.