Given relatively pristine circumstances, a radiocarbon lab can measure the amount of radiocarbon accurately in a dead organism for as long as 50,000 years ago; after that, there's not enough C14 left to measure. Carbon in the atmosphere fluctuates with the strength of earth's magnetic field and solar activity.
When an organism dies it ceases to replenish carbon in its tissues and the decay of carbon 14 to nitrogen 14 changes the ratio of carbon 12 to carbon 14.Experts can compare the ratio of carbon 12 to carbon 14 in dead material to the ratio when the organism was alive to estimate the date of its death.Reimer and colleagues point out that Int Cal13 is just the latest in calibration sets, and further refinements are to be expected.For example, in Int Cal09's calibration, they discovered evidence that during the Younger Dryas (12,550-12,900 cal BP), there was a shutdown or at least a steep reduction of the North Atlantic Deep Water formation, which was surely a reflection of climate change; they had to throw out data for that period from the North Atlantic and use a different dataset.The half-life of an isotope like C14 is the time it takes for half of it to decay away: in C14, every 5,730 years, half of it is gone.
So, if you measure the amount of C14 in a dead organism, you can figure out how long ago it stopped exchanging carbon with its atmosphere.
It was the first absolute scientific method ever invented: that is to say, the technique was the first to allow a researcher to determine how long ago an organic object died, whether it is in context or not.
Shy of a date stamp on an object, it is still the best and most accurate of dating techniques devised.
So, in other words, we have a pretty solid way to calibrate raw radiocarbon dates for the most recent 12,594 years of our planet's past.
As you might imagine, scientists have been attempting to discover other organic objects that can be dated securely steadily since Libby's discovery.
Radiocarbon dating is one of the best known archaeological dating techniques available to scientists, and the many people in the general public have at least heard of it.