How come an animal's carbon-14 levels do not start to decrease until it dies?
A)because it constantly replenishes its carbon-14 supply by eating plants with carbon-14 in them
B)because it constantly replenishes its carbon-14 supply by breathing air with carbon-14 in it
C)because it is constantly being bombarded with cosmic rays
D)carbon-14 only starts to decay after the animal dies
E)The carbon-14 levels do not decrease because the carbon-13 in its skin protects it from cosmic rays.

Question

Quizplus · Accepted Answer

Carbon-14 is a radioactive isotope of carbon that is constantly being replenished in living organisms by the intake of food and water. When an organism dies, the intake of carbon-14 stops, and the amount of carbon-14 in the organism begins to decrease as it decays into nitrogen-14.

How Come an Animal's Carbon-14 Levels Do Not Start to Decrease