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# The half-life of 14C is approximately 5,730 years, while the half-life of 12C is essentially infinite.?

If the ratio of 14C to 12C in a certain sample is 25% less than the normal ratio in nature, how old is the sample?

The answer to this question is "Less than 5,730 years" but I am having a very difficult time understanding why. If there is less Carbon-14 than normal in a sample, wouldn't that mean more of it has decayed because it is older?

### 1 Answer

- 9 years agoFavorite Answer
Because since the half life is 5730 years, in order for there to have been 25% less than the normal ratio (which is less than the half life), less than 5730 years must have passed.

The half life is 12C is not very relevant in the question as it is only used to reference the half life of the 14C in the sample.

Simple think of it this way. if 5730 yrs had passed, there would be 50% less than the normal ratio because the half life (the time it takes for half the sample to decay) is simple 5730 years.

Since there is a greater amount of 14C present (meaning there is currently 75% present with respect to the normal ratio), the sample must be less than 5730 years old.

Make sense? :)

Source(s): Also a Premed :)