Answer:
The geologists cannot use carbon-14 to date ancient rocks because they are older than 50,000 years .Carbon dating can only be used if the substance is less than 50,000 years of age.As compared to the age of the ancient rocks the carbon-14 decays relatively quickly.Other substances like plants ,animals ,wood and leather ,etc can be dated by carbon-14 because they are younger than 50,000 years of age.Most of the rock of interest is older than this this range and hence geologists use different element which has longer half-life than that of carbon.
