Apatite fission-track dating of one of the Bellante samples confirms the glass age, whereas apatite from the Mosciano S.Angelo sample yields an excessively old age due to the presence in the sample of a significant component of detrital grains.Relative age dating tells us which fossils are older and which fossils are younger. To get an age in years, we use radiometric dating of the rocks.Not every rock can be dated this way, but volcanic ash deposits are among those that can be dated.They build up over time so that that the layers at the bottom of the pile are older than the ones at the top.Geologists call this simple observation the Principle of Superposition, and it is most important way of working out the order of rocks in time.
This anomalous track-diameter distribution is interpreted as a thermal disturbance coeval with the volcanic activity that produced the Pliocene–Pleistocene key volcanic ash bed sampled at Bellante and Mosciano S. The contemporaneity of this ash with the event detected by the Maccarone glass suggests that it was related to the tectonic phase which marked, with numerous erosive levels distributed along the whole Apennine region, the end of the Pliocene sedimentary cycle and the onset of the Pleistocene cycle.Scientists date igneous rock using elements that are slow to decay, such as uranium and potassium.By dating these surrounding layers, they can figure out the youngest and oldest that the fossil might be; this is known as "bracketing" the age of the sedimentary layer in which the fossils occur.Radioactive atoms are inherently unstable; over time, radioactive "parent atoms" decay into stable "daughter atoms." When molten rock cools, forming what are called igneous rocks, radioactive atoms are trapped inside. By measuring the quantity of unstable atoms left in a rock and comparing it to the quantity of stable daughter atoms in the rock, scientists can estimate the amount of time that has passed since that rock formed.Fossils are generally found in sedimentary rock not igneous rock.New dating methods are invented all the time, however, most have practical limitations.