Scientists must assume how much carbon-14 was in the organism when it died.
Complicating matters is the fact that Earth’s carbon-14 concentrations change drastically based on various factors.
Question: "Is carbon dating a reliable method for determining the age of things?
" Answer: Carbon dating, or radiocarbon dating, like any other laboratory testing technique, can be extremely reliable, so long as all of the variables involved are controlled and understood.
Carbon dating therefore relies on enrichment and enhancement techniques to make smaller quantities easier to detect, but such enhancement can also skew the test results. As a result, carbon dating is only plausible for objects less than about 40,000 years old.
Due to all these factors, it’s common for carbon dating results of a particular sample, or even a group of samples, to be rejected for the sole reason that they don’t align with the “expected” results.
That’s not unusual in science, so far as it goes, but the relationship between assumptions and interpretations must be kept in mind. At worst, it can make carbon dating circular and self-confirming, though there are other means of dating that can reduce this risk.
In short, carbon dating is as useful as any other technique, so long as it’s done properly and the results are objectively interpreted.
It is not, however, an inherently error-free or black-and-white method for dating objects.