"Fossils, Rocks and Time"
The “solid” Earth is not so solid: it is constantly changing. The science of Geology provides a
history of these changes.
Parable of the Ant on a Redwood Tree:
There was an ant that lived on a redwood tree. A bird came along and commented on what a nice
home he had and then asked him what he would do when the tree was no more. The ant said
“This tree is unchanging. My father lived here and his father before him, in fact our whole
history has been written on this tree, this tree will not change.”
We know that the tree will change, it grows, branches fall off and branches form. We see the tree
on a human time scale, the ant sees the tree on an ant time scale. The same is true of the Earth.
We view the Earth from human time and see no change but a geologist views the Earth in
Geologic time and sees the Earth as dynamic and ever changing. Historical Geology is the study
of change on the Earth, in both the geologic and biologic realm.
The current body of knowledge in Historical Geology is the result of many years of work by
many scientists in many disciplines. The book outlines accomplishments by some geologists
important to this field.
Steno developed important principles of Geology:
Principle of Superposition: Unless a bed of rock is overturned the layers on the bottom are
older than the layers on the top.
Principle of Original Horizontality: Sediments are laid down horizontally and if tilted become
that way only after deposition.
Principle of Lateral Continuity: Rock units extend outward in all directions until they thin at
the edges or encounter a barrier to original deposition.
Often referred to as the “Father of Geology”, Hutton first recognized the continuity of geologic
Law of Uniformatarianism: states that geologic processes occurring today have occurred in
similar ways in the past. This allows geologists to determine past processes based on landforms
and processes occurring today.
Principle of Biological Succession: particular fossils correspond to particular age rocks and the
relationship between rocks across the Earth can be determined based on the fossils they contain.
Although Lyell is known for his work in the biological field he developed an important principle
Law of Cross Cutting Relations and Inclusions: a rock is younger than any rock it cuts across
and an inclusion is older than any rock in which it is contained.
Charles Darwin developed the idea of natural selection. Natural Selection recognizes that all
organisms of a species are slightly different from one another and that these differences make
some individuals more successful in an environment. “Survival of the Fittest” The more
successful individuals will have more offspring and pass these differences on to their offspring.
Over time a population will change because of these differences. The ENVIRONMENT is the
selector. The environment causes populations to slowly change.