Answer: Carbon Dating though measuring Carbon-14 levels
Explanation:
Scientist measure the age of a fossil determined on the Carbon-14 level compared to the Carbon-12 level. This method works because:
All organisms after their death stop replenishing the amount of carbon in their body. That means that they will have an equal amount of carbon-12 and carbon-14 until they die.
Unlike carbon-12, carbon-14 is unstable and overtime will go through beta decay.
Overtime, a carbon-14 neutron will become a proton and release an electron, transforming into nitrogen-14.
This leads to a drop in carbon-14 level, and because of this, geologist compare the level of carbon-14 to carbon-12 to determine how long it has taken to reach such stage.