Which statement explains why carbon-14 dating cannot be used to date ancient rocks?

• A. Carbon-14 has a relatively short half-life, so it is not detectable in very old rocks.
• B. Carbon-14 dating is only accurate for materials that are millions of years old.
• C. Ancient rocks do not contain any carbon atoms.
• D. Carbon-14 is only produced in rocks, not in living organisms.

Answer: (A)

Verified step by step guidance

1. Understand the principle behind carbon-14 dating: it is based on measuring the amount of carbon-14, a radioactive isotope, remaining in once-living materials to estimate their age.
2. Recall that carbon-14 has a half-life of about 5730 years, which means it decays relatively quickly on a geological timescale.
3. Recognize that because of this short half-life, after about 50,000 to 60,000 years, the amount of carbon-14 left in a sample becomes too small to measure accurately.
4. Apply this knowledge to ancient rocks, which are often millions or billions of years old, meaning any original carbon-14 would have decayed away completely and is no longer detectable.
5. Conclude that carbon-14 dating is not suitable for dating ancient rocks due to the short half-life of carbon-14 and the resulting lack of detectable carbon-14 in very old samples.