Two effects also interfere with the dating of very recent samples.

For example, marine carbon behaves quite differently from carbon in the terrestrial cycle.

The residence time of carbon in the ocean can be measured in hundreds of thousands of years (where the residence time of carbon is defined as the average time an atom of carbon will stay in the ocean).

We can also compare radiocarbon dates with dates known on other grounds.

For example, we have discussed the use of varves for dating; now since varves incorporate organic material as they are formed, we can check that when we radiocarbon date a varve, we get the same date for it as we obtain by counting the varves.

After the death of the organism, processes of decay will return its carbon to the atmosphere, unless it is sequestered — for example in the form of coal.

This means that when an organism is alive, its ratio of C dating, or C-C dating.After about 60,000 years the quantity will be too small for our instruments to measure accurately, and the best we'll be able to say is that the sample is about 60,000 years old or more.For this reason radiocarbon dating is of more interest to archaeologists than to geologists.Since humans eat seafood, this can also affect the carbon dating of humans, and what is worse it does so in an inconsistent manner, since human consumption of seafood varies with location and culture.However, the marine component of diet can be estimated by measuring the ratio of the stable isotopes C in the sample: this will be higher the more seafood the individual consumed.Fortunately it is rarely necessary to use radiocarbon methods to date very recent samples.