Why is carbon-14 dating useful only for relatively recent biological materials?

Carbon-14 dating is primarily useful for biological materials dating back to approximately 50,000 years because of the specific half-life of the carbon-14 isotope, which is 5,730 ± 40 years.123

As a living organism, an individual continuously replenishes its carbon-14 levels through the carbon cycle. Upon death, this intake ceases, and the existing carbon-14 begins to undergo radioactive decay at a constant rate. Because the isotope decays relatively quickly, the amount of carbon-14 remaining in a sample becomes extremely small after tens of thousands of years.123

Once a sample exceeds roughly 50,000 years in age, the remaining concentration of carbon-14 is so low that it becomes difficult to measure accurately. At this point, the technique’s margin of error becomes too large to provide a reliable or useful chronological estimate. Consequently, while the method is a versatile tool for archaeology and late geology, it is limited to relatively recent organic remains.314