If the fossils are found in igneous rock, volcanic ashfall, then you can date the fossils directly. If found in sediments, you date an igneous rock above or below the layer of sediment the fossil was found in. Also, there are marker fossils, which did not exist before a certain time, and were extinct at a certain time. The combination of several of these can also accurately date the age of a fossil. But all of this is wasted on a mind determined to be willfully ignorant.