Paleontology dating fossils
If a fossil has been dated radiometrically in one place, correlation allows use to work out the age in other places.
In the above example, we know that the fossil in Nevada is slightly older than the ash layer dated to 507 million years old.
Leonardo da Vinci (1452–1519), in an unpublished notebook, also concluded that some fossil sea shells were the remains of shellfish.
However, in both cases, the fossils were complete remains of shellfish species that closely resembled living species, and were therefore easy to classify.
In early modern Europe, the systematic study of fossils emerged as an integral part of the changes in natural philosophy that occurred during the Age of Reason.
The nature of fossils and their relationship to life in the past became better understood during the 17th and 18th centuries, and at the end of the 18th century the work of Georges Cuvier ended a long running debate about the reality of extinction and led to the emergence of paleontology, in association with comparative anatomy, as a scientific discipline.
As early as the 6th century BC, the Greek philosopher Xenophanes of Colophon (570–480 BC) recognized that some fossil shells were remains of shellfish, which he used to argue that what was at the time dry land was once under the sea.Not every rock can be dated this way, but volcanic ash deposits are among those that can be dated.The position of the fossils above or below a dated ash layer allows us to work out their ages.We cannot be sure if the rock layers with the same fossils are identical in age.We can say that the rocks formed during the time in which the fossil species lived.
Sedimentary rocks (made from mud, sand, gravel or fossil shells) and volcanic lava flows are laid down in layers or beds.