In high school biology courses they often teach about the inevitable failures of closed systems by taking an aquarium and placing snails, plants and a bowl of water inside; then sealing the aquarium so that no air may get in or out.The idea is that snails produce carbon dioxide which is utilized by the plants, the plants produce oxygen which utilized by the snails. Of course, it doesnt take long before the experiment fails in death for all those in the aquarium.Worse still, sometimes they want to know how evolutionists use Carbon-14 to date dinosaur fossils!
Evolutionists then claim to determine the amount of time since the death of the organism by measuring the current ratio.
The lower the amount of Carbon-14, the longer it has been since death occurred.
As the magnetic field decreases, more cosmic radiation penetrates the earths atmosphere and this causes a slow long-term increase in Carbon-14 production.
These factors combine to cause fluctuations in the Carbon-12/Carbon-14 ratios found in plant, animal and human materials.
There is then a ratio of Carbon-14 to Carbon-12 in the bodies of plants, animals and humans which could be considered as fixed at the time of death.