The Principles of Faunal Succession:
In his most recent book, “The Map That Changed
the World,” Simon Winschester described how William Smith created the
first geologic map in 1815 and in so doing, almost single handedly
established the science of stratigraphy. Using the tennants of
relative dating, Smith noted the geographic
extent of various rocks and fossils throughout England and was able to
create a map that illustrated their distribution. Smith realized
that certain rock layers contained certain types of
fossils. The older the rock, the more primitive the fossil forms
that were present.
Georges Cuvier, the French naturalist, noted Smith’s
results with great interest, and suggested that rocks containing
similar fossils in France were the same age as those in England.
Thus was born the idea that certain types of fossils existed for a
specific period of time in Earth history and that the layers of rock
bearing these fossils could be correlated, or equated to one another,
even over great geographic distances. The Smith-Cuvier
discoveries are termed the “Principle of Faunal Succession” which says
that fossils and groups of fossils exist for limited amounts of time,
and that fossil plants and animals appear in the rock record in a
definitive pattern. Applying Steno’s Laws and the Principle of
Faunal Succession led to the creation of a relative chronology of Earth
history, or the geologic time scale.
(Photo courtesy of The
Changing Earth - Introduction to Geology (2nd ed.), by Mears,
Jr., D. Van Nostrand Co., 1977)
