to the Past
A fossil is a window to the past. It gives us clues
about what life was like in Utah long, long ago.
Most fossils are found in
sedimentary rocks. The plant or animal must be buried quickly, and
remain undisturbed for a long period of time. Usually you will see
fossils of organisms that have hard or bony parts. Soft parts usually
decay before they can fossilize.
There are three kinds of fossils: preserved organisms,
mineral replacement of organisms, and impressions or tracks of organisms.
Remember, an organism is simply something that is or once was living.
Plants and animals are organisms.
Once in awhile you find preserved, unchanged
organisms. An animal that falls through the ice or into a tar pit is
preserved this way. Have you seen insects trapped in amber? Amber is
a yellowish stone from petrified tree sap. Bugs get caught in the sticky
substance and covered. When the sap turns into stone the insect is
Replacement fossils are made when water
dissolves part of the dead plant or animal and washes it away. This
leaves an empty imprint. Minerals fill in the imprint and harden to
form a fossil. Sometimes the minerals fill in so perfectly, that you
can see very detailed parts of the once living organism - like the
rings in a tree trunk. Replacement fossils can be very colorful because
of the minerals involved.
Impressions and Tracks
Impressions are whole organisms, footprints,
or even tail drags. Dinosaur footprints are often found in the roofs
of coal mines in Carbon County. Did the dinosaurs walk upside-down?
No. The coal (formed mainly from plants) is deposited under where the
dinosaur walked. You are looking up at the bottom of the footprints!
|Choose one of the following activities to
make your own fossil:
/ Cast option
you can cut up
or four paper cups
coloring or liquid tempera paint
pan or plate
the sponge into the shape of a plant or animal part. Be creative.
How about a raptor claw or a stegosaurus thigh bone?
the sponge "organism" on the plate.
a "mineral" mixture by doing the following:
a little of each mineral mixture over different areas of the sponge
a few days for the fossil to harden.
your "replacement fossil" and record your observations.
three tablespoons of warm water into each paper cup.
salt into each cup and stir until the mixture is very cloudy.
different color food coloring or paint to each cup and mix
to represent various minerals.
Did the minerals fill in the holes in the organism?
How did the organism stay the same? How did it change?
or plant leaves (Ferns and maples are great!)
paper cut like a tombstone
the leaf on the paper plate. Paint the back side with black paint.
off the extra paint.
place the leaf painted side down on the art paper.
a paper towel over the leaf and gently press down on all parts
of the leaf. (Be sure the leaf doesn't move.)
lift the leaf.
have now made a stamp of your leaf.
How is this procedure different from nature's
method of "stamping?"
- Two colors of clay (homemade or from the store)
- Shells, bones, etc.
- Cooking oil spray
- Flatten a small ball of clay and spray the top
lightly with cooking spray.
- Press the bottom of the shell or bone into
the clay and spray lightly again.
- Flatten another small ball of clay and press
over the top of the shell.
- Carefully separate the two balls of clay and
remove the shell.
- Allow the clay to harden for a few days. You
have two "mold fossils."
In order for a cast fossil to form, the molds must
be filled in with minerals, mud or other sediments and allowed to
- Roll a new color of clay into a small ball
and push it gently into one side of the mold fossil.
- Put the other side of the mold on top and press
- Open the molds and gently remove the "cast
- Allow a day or two for it to harden.