So is everything you eat really radioactive? You bet. Should you worry about
The carbon-14 created by cosmic radiation makes up only a fraction of the
carbon in our atmosphere. But it is there, and just like carbon-12, it can be
taken in by a growing plant and become a part of that plant. (As you may know,
plants take in carbon dioxide, or CO2, separate the
carbon from the oxygen, then release the oxygen back into the atmosphere.)
So every plant contains a certain percentage of carbon-14. And so do those
things that eat plants. And so do those things that eat the things that eat
The percentage of carbon-14 in all of these living things is the same as the
percentage of carbon-14 in the atmosphere. At least it's the same while they're
living. When a plant or animal dies, no carbon (in any form) can enter its
system to become a part of it.
Now we get into the nitty-gritty of carbon dating.
The carbon-14 within every once-living thing will someday turn back into
nitrogen-14. If we knew the amount of carbon-14 a once-living thing had while
it was alive and the rate at which it changed (i.e., how fast it changed) back
into nitrogen, then we could figure out how long ago it lived.
Well, it turns out that we do know. The amount of carbon-14 in the atmosphere
(and therefore in living things) has not changed all that much over time. And
we do know the rate at which carbon-14 changes back to nitrogen-14, though what
this rate is is not as straightforward as it could be.