Download Teacher Background Fossils

Fossils Galore
Teacher Background Information
Students tend to have a natural love for the topic of fossils. Perhaps it is the mystery and magic
of seeing the remains of an extinct creature or the fact that even grown-ups don’t have all the
answers about the past that makes students completely interested in this topic. It is a wonderful
opportunity for you, the teacher, to talk about the process scientists use to learn about the past.
Science involves questioning, investigation, observation, and discovery.
During this mini-unit make a habit of calling your students paleontologists (scientists who study
prehistoric life on Earth). Let students know that paleontologists study prehistoric life by
searching for fossils. Paleontologists are like detectives and fossils are their clues. Fossils are
the traces of the remains or signs of prehistoric animals and plants buried in the Earth’s crust.
They are the hardened remains or imprint of a plant or animal that lived long ago. Fossils are
often found in layers of sedimentary rock and along river beds that flow through them. One
might occasionally find fossils in partly metamorphosed sedimentary rocks, but pressure and
heat usually destroy fossils
In Latin, fossil means “to dig.” The point where fossils are found in the rock layers helps to
determine the time period in which the organism lived. Lower layers of rock are typically older
than upper layers. Some of the oldest fossils are microscopic single-celled organisms and
bacteria. Preserved remains of prehistoric organisms (bones, etc.) are known as body fossils.
Tracks, trails, and other indirect evidence of prehistoric life are called trace fossils. Help
students to see them as more than collectible objects, but as scientific clues of the Earth’s history.
In middle Georgia, one can now find fossilized shark’s teeth. What does that tell us about ancient
Georgia? That the area was at one time covered by the sea!
Fossils are formed in different ways. Dead animals were covered by sediments and their soft
body parts decomposed, but teeth and skeletons remained. They were preserved by hardened
layers of sediment. Water containing minerals can seep into bones, slowly changing them into
stone. An example of this is petrified wood. Some fossils are the actual remains of plants and
animals that have been preserved in amber. Amber is the hardened sap from trees. Some animals
trying to cross tar pits (like those near Los Angeles) became trapped and their remains sank into
the tar material. Their bones have been preserved by the tar. Many fossils are not the actual
remains but are copies of the living organism. Fossil copies are imprints, molds, or casts.
Imprints are impressions made by organisms in mud that were preserved when the mud
solidified. Hardened tracks of animals or the burrows of prehistoric worms in solidified mud are
examples of fossil imprints. Molds were made when an organism was totally or partially buried
in mud. The mud hardened into rock and over time ground water dissolved the organism. All
that was left was a cavity shaped like the organism. If a mold was later filled in with mud or a
mineral material (think of filling a play dough mold with play dough), the filling hardened into
what we call a cast. A cast, rather than looking the imprint of the organism, looks like the
organism itself. A common practice of paleontologists is to make cast of fossil molds by filling
them with plaster and then letting it harden.
S3E2a & 2b
27
GYSTC
Background
Fossil fuels refer to oil, natural, gas, and coal. These fuels were formed millions of years ago.
Coal was created from plants that decayed and oil and natural gas were formed from the remains
of marine organisms. Over time, these animals and plants were buried deep under layers of sand
and silt. Intense heat and pressure squeezed and buried the organisms so much that they slowly
changed into fossil fuels.
S3E2a & 2b
28
GYSTC
Background