Question: What happens to the Carbon-14 when plants and animals die? 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. Question:
What does radioactive half-life mean? Answer: Carbon -14 has a half-life of 5730 years. This is the time it takes for half of the carbon-14 to decay. 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. Know that not all of the carbon-14 atoms decay at the same time, but the half-life describes how long it takes for half of them to decay. Some radioactive isotopes decay very rapidly, in fractions of a second, while others might take hundreds of thousands or even millions of years.
Question: What is C-14 dating? Answer: Scientists determine the age of a fossil by determining the amount of Carbon -14 that has decayed since the organism died and was buried in the ground. The original percentage of carbon-14 in an organism is the same as the percentage of carbon-14 in the environment today. One assumes that the percent of C-14 in the environment has not changed (there is a chart that can be used to include fluctuations but for most science classes it is not considered).
Question: How is the amount of C-14 in a fossil determined?
Answer:
Since 1 gram of carbon-14 emits 15 beta particles per minute, the mass of carbon-14 in a fossil can be determined by measuring its rate of beta particle emission. 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
CARBON-14 DATING
For a website with good diagrams about carbon-14 dating, see MORE CARBON-14 DATING
For Advanced Learners
Question: How is time determined using the half-life of an element?
Answer:
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).
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).
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
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