Paleontology is key to the study of evolution for two reasons.
- The discovery of fossils showing forms of animals that had never previously
been seen began to cast serious doubt upon creationist
theories.
- Fossils provide the only direct evidence of the history of evolution.
Today, whereas molecular biology might be used to study
microevolution, or the development of individual species,
paleontology is used to study
Macroevolution,
or large evolutionary trends.
Techniques and Principles of Paleontology
What is a fossil? Generally, we think of bones, shells, or teeth that are
buried in rock, but fossils can also be outlines of leaves or footprints or
trails. This second set of fossils, which are the outlines of items from the
past rather than the items themselves, are called trace fossils. Fossils
are formed when sediment covers some material, such as a piece of bone. Very
gradually, the bone becomes impregnated with chemicals from the surrounding
rock. Eventually all that remains is essentially a piece of rock in the shape
of the original bone, or material.
Taken together, fossils can be used to construct a fossil record, which is a
timeline of fossils reaching back through history. Several factors must be
taken into account when constructing such a record. The strata of rock in which
fossils are found give us clues about their relative ages. Similarly, new
technological techniques such as radioactive carbon dating help determine the
absolute ages of fossils. In addetion to supplying a fossil's relative age,
rock strata can also give clues about the environments in which an animal or
plant lived. The chemical make-up of these strata can tell us the balance of
gases in ancient atmospheres. Major cataclysmic events such as eruptions and
meteor strikes also leave there mark on the fossil record.
There are, however, limitations on the information fossils can supply.
Fossilization is an improbable event. Most often, bones and other materials are
crushed or consumed before they can be fossilized. In addition, fossils can
only form in areas where sedimentary rock is formed, such as ocean floors.
Organisms that live in these environments are therefore more likely to be
fossilized. Erosion of exposed rock faces or through the crushing action of
geological movements can destroy fossils even after they are formed. All of
these conditions lead to large and numerous gaps in the fossil record.
The Brief History of Life
provides, as you might expect, a synopsis of the history of life that has been
determined through fossil records.
