WHAT IS A FOSSIL?
Fossils are the remains of plants or animals or the physical records of their presence in prehistoric times. The definition also includes early man-made tools and human remains that greatly predate written records. The study of fossils is called paleontology. One who studies fossils is a paleontologist.
WHY STUDY FOSSILS?
In a pragmatic society, the question "Why
should we study this?" is often asked. The study
of paleontology offers many answers:
- Organic evolution - Sedimentary rock documents
the occurrence of life on earth from the
simpler organisms to the most complex plants
and animals. Of course, the record is incomplete.
But with what there is, the student can
trace much of the evolution of life on earth. A
dramatic example of this is the fossil of the
extinct Archaeopteryx, the so-called "link"
between reptiles an d birds. Without this fossil
and the discovery of many new types of feathered
reptiles and early birds from China, the
conclusion that birds evolved from reptiles
would be a great deal more questionable.
- Biostratigraphy - Fossils aid the paleontologist in dating rock. All species of animals and
plants lived only during certain intervals of
time. This time interval is bracketed by their
earliest appearance as a result of their evolution
and their last occurrence just prior to their
extinction. Consequently, fossil remains will
position the rocks in which they are found in a
sequence from oldest to youngest. This is
especially important in oil drilling, as certain
fossils are the keys to the age of specific subsurface
rock formations, some of which are
know to be oil-bearing. The use of fossils in
relative time dating is called biostratigraphy.
- Geochronology - Fossils can sometimes be
dated in an absolute sense, that is, in terms of
an actual age in years. Absolute age dating, or
geochronology, includes the carbon-dating of
relatively young (up to 50,000 years ago) wood
or the dating of radioactive minerals found
with older fossils. Once a relatively old fossil
is dated at one locality, the presence of this
same fossil can be used to approximate the age
of the enclosing rock at other places.
- Environment - Modern and ancient organisms
are limited to specific habitats. Ancient
environments can be reconstructed by studying
features preserved in the rocks and by
comparing them with features known in modern
sediments and modern environments. For
example, rocks that preserve root horizons,
ancient soil horizons, and stream deposits
were laid down on land. It is also known that
much of the inland United States was covered
several times by shallow seas over the last 500
million years. This is proven by the evidence
of marine fossils in these rocks. It can also be
shown that the present north and south poles
were once warm by pointing to fossilized tropical swamp plants that are now found in polar
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