Geologists have studied the order in which fossils appeared and disappeared through time and rocks. Fossils can help to match rocks of the same age, even when you find those rocks a long way apart.This matching process is called correlation, which has been an important process in constructing geological timescales.Some fossils, called index fossils, are particularly useful in correlating rocks.
The regular order of occurrence of fossils in rock layers was discovered around 1800 by William Smith.
The realization that sediments turn into rock was counter to the view that all rocks on Earth formed in a single creation event.
Once Steno recognized that the fossils he was contemplating (sharks teeth and sea shells) were formed in the sediments of oceans he was able to work out the basic rules of stratigraphy.
A chance encounter between determined fishermen and a great white shark off the Tuscan coast in 1666 sparked a chain of events that would help change humans views of fossils and Earth’s geologic past (Cutler 2003, pp. Nicolas Steno (1638-1686) dissected the head of this shark and realized fossil tongue stones believed to be petrified snake or dragon tongues were actually fossil shark teeth (Prothero 1998, p. One problem still existed, how do fossils become embedded in solid rock?
Steno recognized that fossils represent organisms that became buried in sediment, which later turned into rock.