To radiocarbon date an organic material, a scientist can measure the ratio of remaining Carbon-14 to the unchanged Carbon-12 to see how long it has been since the materials source died. Advancing technology has allowed radiocarbon dating to become accurate to within just a few decades in many cases.
Why is carbon-14 not the best for dating rocks?
Over time, carbon-14 decays radioactively and turns into nitrogen. Because of the short length of the carbon-14 half-life, carbon dating is only accurate for items that are thousands to tens of thousands of years old. Most rocks of interest are much older than this.
What are the limitations of carbon-14?
Inorganic materials cant be dated using radiocarbon analysis, and the method can be prohibitively expensive. Age is also a problem: Samples that are older than about 40,000 years are extremely difficult to date due to tiny levels of carbon-14. Over 60,000 years old, and they cant be dated at all.