Why are carbon 14 levels consistent in living things?
It help, first, to know something about carbon and where it comes from. it has been estimated that carbon is the fourth most abundant chemical element in the universe. But it is not very abundant on the earth. It makes up only about 0.032% of all the matter all around us even though we are, as a living creature, about 18% carbon.
Stable carbon, essential to life, as we understand it, was not formed in the Big Bang or at any time during the early history of the universe. It was created much later, after stars were formed. Physicists believe that it was formed by a two-step nuclear fusion that could take place in only the hottest of the most massive stars. Carbon probably arrived on earth as dust from supernova explosions that happened billions of years ago. Our solar system was created from that dust and other material that arrived from far away stars. The isotope carbon 14 is the exception. Carbon 14 is created in the Earth's atmosphere above 30,000 feet.
Our world is constantly bombarded by tiny subatomic particles from outer space. Some of these particles come from our sun. Others arrive from far away in our galaxy. Some come from beyond our own galaxy, from the farthest reaches of the universe. These particles may have travelled for billions of years before entering our atmosphere where they collide with oxygen or nitrogen atoms. When this happens, they unleash a witch’s brew of new particles, which in turn smash into other atoms, unleashing even more sub-atomic particles. Some, either the ones from outer space or the ones produced in our atmosphere make it to the surface of the earth. (You were struck thousands of times while reading this far on this web page.) Some like neutrinos may pass right through you, and then pass through the entire earth, then go off into space never to be encountered again. Some neutrons, on the other hand, interact with nitrogen atoms in the upper atmosphere, specifically nitrogen 14, the most common form of nitrogen. When they do they turn the nitrogen atom into a carbon 14 atom.
When carbon atoms, all types, meet oxygen atoms, and the circumstances are right, the atoms combine to form the chemical compound carbon dioxide (CO2). The oxygen atoms are not fussy because they don’t care if the carbon atom is good old fashioned stable carbon or the radioactive variety.
Then, because air in the atmosphere is always in motion, going sideways and up and down, the carbon dioxide with the unusual carbon 14 atom is fully mixed together with all other carbon dioxide molecules in the lower atmosphere. Plants use carbon dioxide in photosynthesis to create a host of organic compounds, mainly sugars. Those compounds, when formed, have carbon 14 atoms. Animals eat plants or the eat the flesh of animals that eat plants and so those one-in-a-trillion carbon 14 atoms get spread around among all living things in the same proportions found in the atmosphere. That means, that that while we are alive, one in every trillion of the trillions and trillions and trillions of carbon atoms that make up you and me, is a carbon 14 atom.
Carbon 14 atoms are radioactive, unstable. That means that they decay. They convert themselves into nitrogen 14 atoms. But they do so slowly and as long as we are alive, we continue to take on new carbon 14 and maintain consistent levels of the isotope. Beginning with our death, the number of carbon 14 atoms disintegrate and over time the there are fewer and fewer carbon 14 atoms in what remains of us. By measuring the amount of remaining carbon 14 atoms we can determine how long it has been since death.
- What is carbon dating?
- Carbon dating in 1988
- What do you mean, carbon 14 is radioactive?
- Astonishing balancing act in nature
- Why are carbon 14 levels consistent in living things?