Approximately how far back can carbon-14 dating reliably date?

• A. 5,000 years
• B. 500 years
• C. 5 million years
• D. 50,000 years

Answer: (D)

Carbon-14 dating relies on measuring the ratio of carbon-14 to carbon-12 in once-living material and using the known half-life to estimate age. The half-life of carbon-14 is about 5,730 years, so the amount left declines exponentially with time. In practice, dating is reliable up to roughly fifty thousand years because, after that many half-lives, the remaining carbon-14 is extremely small and difficult to detect accurately; even small contamination or calibration issues can create large errors. This limit makes carbon-14 dating useful for relatively recent fossils and artifacts, but not for very old materials. Hence, the best choice is around fifty thousand years.