So by measuring the C-14 level we work out how many half lives old the sample is and therefore how old it is.
The trouble is that after 40,000 years there is under 1% of the original C-14 left, and it becomes too hard to measure it accurately.
Thus creationists and others who invoke perceived weaknesses in radiocarbon dating as justification to cast doubt on the great age of the earth are either uniformed on very basic scientific facts, or else are highly being disingenuous to their audience.
Radiocarbon dating has been studied at great length over the past few decades, and its strengths and weaknesses are very well understood at this point in time.
This isn't a fundamental limit as more accurate measurements could go further back, but at some point you'd simply run out of C-14 atoms.
With our current kit 40-50K years is about the limit.
Because of this relatively short half-life, radiocarbon is useful for dating items of a relatively recent vintage, as far back as roughly 50,000 years before the present epoch.
half the original level, we know the sample is around one half life or 5,700 years old.
Creationists often criticize radiocarbon dating in the context of discussions of the age of the earth.
But, as is clear even from the very brief discussion in the previous paragraph, radiocarbon dating can say nothing one way or the other about whether the earth is many millions of years old, since such dates are far beyond this method's range of resolution.
For an example, when they tried to get the carbon dating for presence of Aboriginal people in Australia they get to the number 40,000. Why is that 40,000 years limit for carbon dating methods?
Carbon-14 makes up about 1 part per trillion of the carbon atoms around us, and this proportion remains roughly constant due to continual production of carbon-14 from cosmic rays.
Levels of carbon-14 become difficult to measure and compare after about 50,000 years (between 8 and 9 half lives; where 1% of the original carbon-14 would remain undecayed).
The question should be whether or not carbon-14 can be used to date any artifacts at all? There are a few categories of artifacts that can be dated using carbon-14; however, they cannot be more 50,000 years old.
Radiocarbon dating, which is also known as carbon-14 dating, is one widely used radiometric dating scheme to determine dates of ancient artifacts.
In discussions of the age of the earth and the antiquity of the human race, creationists often assail perceived weaknesses in radiocarbon dating. Morris, for instance, wrote, "Despite its high popularity, [radiocarbon dating] involves a number of doubtful assumptions, some of which are sufficiently serious to make its results for all ages exceeding about 2000 or 3000 years, in serious need of revision." [Morris2000, pg. Radiocarbon dating is based on the fact that the interaction of cosmic rays from outer space with nitrogen atoms in the atmosphere produces an unstable isotope of carbon, namely radiocarbon.
After all, this what the archeologist guessed in their published books.
Some believe trees are known to be as old as 9,000 years. A lot of people doubt this claim for various good reasons I wont go into here.