How is the half life of carbon 14 dating used?
Carbon-14 dating is used for determining the age of archaeological artifacts of biological origin (could be bone, fiber, wood, plant remnants etc.) up to about 50,000 years old.
For this, If a fossil has say 25% of carbon-14 as compared to living sample than it is 11460 years old (as it has one-fourth carbon it is 5730*2=11460 years old).
General formula for time