Plants and animals absorb both C-12 and C-14 in the course of their natural lifetimes simply by carrying out these basic functions.When they die, they cease to consume them, and the isotope of C-14 begins to revert back to its Nitrogen state at an exponential rate due to its radioactive decay.Carbon dioxide in the atmosphere contains a constant amount of carbon-14, and as long as an organism is living, the amount of carbon-14 inside it is the same as the atmosphere.
This property makes it especially useful in a process known as “radiocarbon dating”, or carbon dating for short.
Radiocarbon enters the biosphere through natural processes like eating and breathing.
On the other hand, atmospheric testing of nuclear weapons during the 1950s and 1960s is likely to have increased the Carbon 14 content of the atmosphere.
In fact, research has been conducted which suggests that nuclear tests may have doubled the concentration of C-14 in this time, compared to natural production by cosmic rays. If you’d like more info on Carbon Dating, check out NASA’s Virtual Dating: Isochron and Radiocarbon – Geology Labs On-line, and here’s a link to USGS Radiometric Dating Page.
The ratio of normal carbon (carbon-12) to carbon-14 in the air and in all living things at any given time is nearly constant.
Maybe one in a trillion carbon atoms are carbon-14.
The carbon-14 atoms are always decaying, but they are being replaced by new carbon-14 atoms at a constant rate.
At this moment, your body has a certain percentage of carbon-14 atoms in it, and all living plants and animals have the same percentage.
The carbon-14 atoms that cosmic rays create combine with oxygen to form carbon dioxide, which plants absorb naturally and incorporate into plant fibers by photosynthesis.
Animals and people eat plants and take in carbon-14 as well.
Nevertheless, it remains the most accurate means of dating the scientific community has discovered so far. We’ve also recorded an entire episode of Astronomy Cast all about How Carbon Dating Works.