If the scientist can find out how much of this material was in the bone when the animal died, and if he knows how fast it disappears, and if he can measure the amount still left in the bone, he has something like a natural hourglass. Carbon is one of the most important atoms in the living system.
Carbon is present in proteins, fats and carbohydrates – the three basic foods.
C-14 enters the air by the action of cosmic radiation.
Cosmic rays enter our Earth's atmosphere from outer space.
But that's not really how it is when scientists are working in their labs.