How does radiocarbon dating or carbon-14 dating work?

Answer 1

Radiocarbon Dating
All organic matter contains carbon, which is an element. But there are different types of carbon, called isotopes. The most common isotope is carbon-12 (or 12C), which (according the article) makes up 98.89 percent of the naturally occurring carbon. There's carbon-13, or 13C, which is much rarer, accounting for only 1.11 percent, and then there's carbon-14, or 14C, which makes up a ridiculously tiny fraction of existing carbon. (The Periodic Table of the elements also reflects the existence of isotopes by showing a weighted average for the atomic weight of each element, but I digress.)

The first two isotopes, 12C and 13C, are stable, but 14C is unstable; that is, it's radioactive! So far, so good. Nothing hard to get your brain around. Living organic matter will have steady and predictable concentrations of each isotope of carbon, pretty much the percentages mentioned above. But dead stuff won't. After something dies, the 14C decays over time (because it is radioactive) and doesn't replenish as it would in a live specimen because the dead thing isn't eating and breathing or otherwise exchanging molecules with the outside world anymore). In other words, the amount of 14C in dead organic matter will grow smaller. And since scientists know exactly how long an amount of 14C takes to decay, they can compare the amount of 14C in a specimen to the amount of 14C a modern piece of organic matter and calculate the age of the specimen. Since it takes 5,568 years for an amount of 14C to decay by 50 percent (half), if a specimen has one half the amount of 14C as a modern piece of organic matter might have, we conclude it is about 5,568 years old.

Here's an analogy: Imagine you have a gallon of water to which you add one ounce of blue dye. And say that every 5,568 years you add another gallon of water to the mixture. Doing that basically cuts the concentration of blue dye in half. You then take a gallon of that diluted mixture and add another gallon of pure water to it 5,568 years later. The concentration of blue dye is cut in half again. Now imagine repeating this process for quite some time. If you take a sample of the diluted water and measure the concentration of blue dye, you will be able to determine how many dilutions took place, and since you know the dilutions happen every 5,568 years, you can estimate how old the sample is. See link below for more information.

Answer
Carbon-14 builds up in living tissue at a constant rate and starts to break down when the tissue dies. Scientists can measure the amount of carbon-14 in a piece of old wood for instance, and say that because there is only a certain amount left, the tree died 1000 years ago.

Answer 2

Radiocarbon dating is an radioactive isotope dating technique used in dating materials which contain the unstable carbon-14 isotope. Radiocarbon dating is used to determine the age of previously living organisms.

Answer 3

Carbon is a naturally abundant element found in the atmosphere, in the earth, in the oceans, and in every living creature. C-12 is by far the most common isotope, while only about one in a trillion carbon atoms is C-14. C-14 is produced in the upper atmosphere when nitrogen-14 (N-14) is altered through the effects of cosmic radiation bombardment (a proton is displaced by a neutron effectively changing the nitrogen atom into a carbon isotope). The new isotope is called "radiocarbon" because it is radioactive, though it is not dangerous. It is naturally unstable and so it will spontaneously decay back into N-14 after a period of time. It takes about 5,730 years for half of a sample of radiocarbon to decay back into nitrogen. It takes another 5,730 for half of the remainder to decay, and then another 5,730 for half of what's left then to decay and so on. The period of time that it takes for half of a sample to decay is called a "half-life."

Radiocarbon oxidizes (that is, it combines with oxygen) and enters the biosphere through natural processes like breathing and eating. Plants and animals naturally incorporate both the abundant C-12 isotope and the much rarer radiocarbon isotope into their tissues in about the same proportions as the two occur in the atmosphere during their lifetimes. When a creature dies, it ceases to consume more radiocarbon while the C-14 already in its body continues to decay back into nitrogen. So, if we find the remains of a dead creature whose C-12 to C-14 ratio is half of what it's supposed to be (that is, one C-14 atom for every two trillion C-12 atoms instead of one in every trillion) we can assume the creature has been dead for about 5,730 years (since half of the radiocarbon is missing, it takes about 5,730 years for half of it to decay back into nitrogen). If the ratio is a quarter of what it should be (one in every four trillion) we can assume the creature has been dead for 11,460 year (two half-lives). After about 10 half-lives, the amount of radiocarbon left becomes too miniscule to measure and so this technique isn't useful for dating specimens which died more than 60,000 years ago. Another limitation is that this technique can only be applied to organic material such as bone, flesh, or wood. It can't be used to date rocks directly.