The temperature at which this happens is known as the closure temperature or blocking temperature and is specific to a particular material and isotopic system. They are not calibrated by fossils. This includes factoring in many variables, such as the amount of radiation the object was exposed to each year. Some [skeptics] make it sound like there is a lot of disagreement, but this is not the case. Search for: Evidence for evolution radioactive dating The strongest direct evidence for its vast evolutionary geologist that can observe how long ago rocks formed, into a way of carbon
However, to discover how tool use relates to human evolution, scientists must be able to date it. Fossils often have no carbon in them at all. Obviously Carbon 14 can not be used in mineralized fossils.