Carbon 14 dating for kids
Once the organism dies, however, it ceases to absorb carbon-14, so that the amount of the radiocarbon in its tissues steadily decreases.Carbon-14 has a half-life of 5,730 ± 40 years—, half the amount of the radioisotope present at any given time will undergo spontaneous disintegration during the succeeding 5,730 years.
It is assumed that the ratio has been constant for a very long time before the industrial revolution. (For on it hangs the whole validity of the system.) Why did W. Libby, the brilliant discoverer of this system, assume this?The fact that the C doesn’t matter in a living thing—because it is constantly exchanging carbon with its surroundings, the ‘mixture’ will be the same as in the atmosphere and in all living things.As soon as it dies, however, the C ration gets smaller.This means that he thought that C was entering the atmosphere as fast as it was leaving—calculations show that this should take place in about 30,000 years, and of course the Earth was much older than that, said the geologists.Imagine a tank with water flowing in at a certain rate, and flowing out again at the same rate (see diagram below). If you saw it for the first time, you wouldn’t be able to work out how old it was—how long it had been since it was ‘switched on’.Question: What happens to the Carbon-14 when plants and animals die? This is the time it takes for half of the carbon-14 to decay.
Answer: When organisms containing C-14 die, there is no further intake of Carbon 14, so the Carbon- 14 concentration slowly decreases as individual unstable Carbon- 14 decay back into stable Nitrogen -14 atoms. For example, if the organism had 100 grams of carbon-14 when it died, after 5730 years the fossil would have 50 grams of carbon-14.
So, if you had a fossil that had 10 percent carbon-14 compared to a living sample, then that fossil would be: t = [ ln (0.10) / (-0.693) ] x 5,700 years t = [ (-2.303) / (-0.693) ] x 5,700 years t = [ 3.323 ] x 5,700 years t = 18,940 years old Math Skills Using natural logs (loge or ln): Carrying all numbers to 5 significant figures, ln 30 = 3.4012 is equivalent to e3.4012 = 30 or 2.71833.4012 = 30 A formula to calculate how old a sample is by carbon-14 dating is: t = [ ln (Nf/No) / (-0.693) ] x t1/2 where ln is the natural logarithm, Nf/No is the percent of carbon-14 in the sample compared to the amount in living tissue, and t1/2 is the half-life of carbon-14 (5,700 years).
Radio carbon dating determines the age of ancient objects by means of measuring the amount of carbon-14 there is left in an object.
Knowing this and an estimated amount of carbon-14 in the organism while alive can be used to determine the age of the fossil.
For a website with a simple calculator that computes this for you, see is the half-life of carbon-14 (5,700 years).
Radiocarbon present in molecules of atmospheric carbon dioxide enters the biological carbon cycle: it is absorbed from the air by green plants and then passed on to animals through the food chain.