Trees maintain carbon 14 equilibrium in their growth rings—and trees produce a ring for every year they are alive.Although we don't have any 50,000-year-old trees, we do have overlapping tree ring sets back to 12,594 years.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.But before that, only fragmentary data is available, making it very difficult to definitively date anything older than 13,000 years.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.You have to know what the atmospheric carbon level (the radiocarbon 'reservoir') was like at the time of an organism's death, in order to be able to calculate how much time has passed since the organism died.
The dates and corresponding environmental changes promise to make direct correlations between other key climate records, allowing researchers such as Reimer to finely calibrate radiocarbon dates between 12,500 to the practical limit of c14 dating of 52,800.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.Yet, you’ve heard the news: Earth is 4.6 billion years old. That corn cob found in an ancient Native American fire pit is 1,000 years old. Geologic age dating—assigning an age to materials—is an entire discipline of its own.