Fossil Background Information for Hunting Fossils Lab
Most of the information scientist have about Earth’s past comes from rocks. Most rocks
form in layers over many thousands of years. By studying these layers scientists called
geologists can figure out what conditions may have been like when each layer was
formed. Rocks formed in warm climates contain more fossils than those formed in cooler
climates. Rocks which are on the Earth’s surface during the ice ages show signs of being
worn away by glaciers.
Life on Earth
The Earth is the only planet on which life is known to exist. To survive, living things
need the right amounts of light and heat from the Sun, along with food, water, and
oxygen. It has taken many millions of years for conditions on Earth to become suitable
for the wide variety of plants and animals which exist today.
Scientists measure the Earth’s ancient past in geological (deep) time. This divides into 4
eras which break down further into periods of several million years. Evidence from rock
formations suggests that 5 mass extinctions events have taken place in the Earth’s past.
During each one, huge numbers of living things died out in a very short time. Only
organisms which were best suited to conditions on the Earth at the time survived and
multiplied.
Fossils
Fossils are the remains of once living animals or plants. People have been finding fossils
in rocks for thousands of years, but until quite recently they didn’t understand what they
were. Today we know that the fossils we find in rocks represent the ancestors of the
animals and plants alive today.
Often when people think of fossils they think of dinosaur skeletons and large bones. But
there are many different types of fossils to be found. Paleontologists, scientist who study
fossils, divide them into 2 major types- body fossils and trace fossils.
The first type, body fossils, is the fossilized remains of an animal or plant, like bones,
shells or leaves. This type of fossil shows us what and animal or plant looked like. These
include bones, teeth, skin impressions hair, the hardened shell of an invertebrate,
impression of an animal or plant. These are mold or cast fossils (*see below), like
petrified wood, or whole body fossils- mammoths caught in ice, or insects trapped in
petrified tree sap (amber).
The second type of fossil records the activity of an animal. Known as trace fossils, these
include footprints, trackways (burrows) and coprolites (fossil poop!). Trace fossils
show evidence about how an animal lived.
What can fossils tell us?
Fossils give information about how animals and plants lived in the past. Some fossils are
easy to identify because they look like the plants and animals alive today. While we can
easily recognize and identify some fossils, many fossils represent animals or plants that
no longer exist on Earth. We only know about extinct groups like dinosaurs, ammonites
(an extinct invertebrate ocean animal with a flat partitioned spiral shell), and trilobites
( an extinct Paleozoic ocean arthropod with a flat oval body and dorsal exoskeleton
divided into tree vertical sections.) through fossils. By studying the fossils record we can
tell how long life has existed on Earth, and how different plants and animals are related to
each other. Often we can figure out how and where they lived and then use this
information to find out about ancient environments.
How do fossils form?
When an animal or plant dies its remains usually rot away to nothing. Sometimes
though, when the conditions are just right and its remains can be buried quickly, it may
become fossilized. There are several different ways fossils are formed. There are 5 steps
of fossilization to make a typical *‘mold and cast’ fossil.
1. An animal dies, its skeleton settles on the sea floor and is buried by sediment. The soft
parts of the animal rot away, leaving only its skeleton. The skeleton is buried by sediment
(like sand or mud) falling from the ocean above. The sea floor is an ideal place for
fossilization, which explains why many fossils are marine animals (from animals that
lived in the sea). Land animals may die and be swept out to sea to be buried in the same
way.
2. The sediment surrounding the skeleton thickens and begins to turn to stone. The
skeleton continues to be buried as sediment is added to the surface of the sea floor. As
the sea floor sinks, pressure increases in the lower layers of sediment and turns it into
hard rock.
3. The skeleton dissolves and a mold is formed. Now buried at depth and surrounded by
stone, the skeleton is dissolved by ground water. This leaves a cavity (or hole)
preserving the shape of the original skeleton. This cavity is known as a natural mold.
4. Minerals crystallize inside the mould and a cast is formed. Water rich in minerals
enters the mold, and fills the cavity. The minerals deposited in the mould form a cast of
the mold. This cast has the same shape as the original skeleton, but none of its internal
features.
5. The fossil is exposed to the Earth’s surface. Millions of years later, the rock
surrounding the skeleton rises to the Earth’s surface (this happens during mountain
building, earthquakes and other earth processes). The rock is worn away by wind and
rain, and the fossil is now exposed, waiting to be found!
Other types of Fossilization
Refrigeration: This is the best means of preservation of ancient materials. It happens
only rarely. The animal must be continually frozen from the time of death until
discovery. There have been remarkable discoveries of mammoth and wooly rhinoceros
found in ice from Alaska, and Siberia. Specimens with flesh, skin, and hair intact have
been found. Some of these suggest they were flash frozen, with food still in the mouth
and stomach.
Drying (desiccation) - Mummified bodies of animals including humans have been
discovered in arid parts of the world. The soft tissues including skin and organs are
preserved for thousands of years if they are completely dried.
Fossils formed in asphalt- In downtown Los Angeles lies a 23 acre park called the La
Brea Tar Pits. Within the park are over 100 pits filled with sticky asphalt or tar. The tar
pits were formed by crude oil seeping through fissures in the earth. The pits are famous
for the number and high quality of Pleistocene (an epoch of geological time about 1.610,000 years ago) fossils that have been pulled from the pits. The fossils from these pits
date between 10 and 40 thousand years old. Asphalt is an excellent preservative. Bones,
teeth, shells, the exoskeletons of insects, and even some plant seeds have been pulled
from the pits.
Fossils formed in amber- Insects, spiders, and even small lizards have been found
nearly perfectly preserved in amber. Say a fly lands on a tree branch and steps in sticky
tree sap. As the fly struggles to escape it becomes more and more entombed in the sap
until it completely is engulfed and suffocates. The tree eventually dies and falls into a
swampy water where it grew. Over millions of years the tree along with countless others
becomes a coal deposit and the sap with the fly inside is polymerized and hardened into
amber. As more time passes the coal bed is submerged as the sea level rises. Eventually
the currents uncover the coal bed, slowly eating into the surface, little by little. When the
erosion reaches the amber, it floats to the surface because it is lighter than the salty water.
It is then washed ashore where it can be found.
Fossils formed by carbonization- In this process of fossilization plant leaves and the
soft body parts of fish, reptiles and marine invertebrates decompose leaving behind only
the carbon. This carbon creates an impression in the rock outlining the fossil, sometimes
with great detail.
Fossils formed by per mineralization- This is the most common method of fossil
preservation. Minerals fill the cellular spaces and crystallize. The shape of the original
plant or animal is preserved as rock. Sometimes the original material is dissolved away
leaving the form and structure but none of the organic material remains.
Internet Links (for more information)
www.usborne-quicklinks.com
web site 1 Explore Earth’s history
web site 2 Find our about the history of the study of dinosaurs
web site 3 Find out about fossils, extinction, climate change and more
http://www.fossils-facts-and-finds.com information about fossilization
(both web sites very kid friendly)
Finding Fabulous Fossils Lab
Science Standards Frameworks for this lab1.1 Identify and develop a testable question.
1.1e-Develop and communicate logical conclusions and make
predictions based on evidence from an experiment.
1.2c-Represent data and evidence from an experiment in visual form
(e.g. data tables, graphs, diagrams).
4.1-Predict or infer how fossils are formed from previously living
organisms
Objective: Students discover fossils (shark teeth) in a sphere of soil
and sand. Using a small brush and nail, students pick at the ball of
dirt to slowly uncover the fossil (shark tooth) inside. Using the nail,
students slowly pick apart the dirt. Students brush away the extra dirt
using the brush to help to scrape off the dirt onto the tray. With the
hand lens or magnifying glass students observe their finding. They
then record their finding by drawing the shark tooth or bone fragment
onto the grid paper provided. Students complete the form filling in the
information and adding details to their drawing and labeling their
finding. (Students can glue this form into their Science Notebook.)
Students may keep what they find.
Materials for Lab:
I tray per 2 students
On each tray:
1 sphere of dirt and sand with shark tooth or bone fragment
embedded in the sphere. Two fossils per sphere.
2 long nails
2 brushes
1 hand lens or magnifying glass
2 copies of Fossil Catalog Card (One copy per student )
Pencils and erasers as needed on table
Student Science Notebooks
Plan for Lab
1. Invite students to use the brush and nail to gently pick away the
dirt on their dirt ball. (Encourage students to keep as much dirt on the
tray.)
2. Encourage students to look through hand lens to observe the dirt
and then the fossils they find.
3. When students have found the fossil hidden in the dirt ball,
students should look at it with the magnifying glass or hand lens.
4. Students using a pencil from the center of the table draw their
fossil only on the catalogue card provided, one catalogue card per
student. Please have student label their drawing.
5. Students then identify the fossil they found from the Fossil Shark
Tooth Key Cards on the table.
Students may keep fossils they find.
6. Teachers: PLEASE place excess dirt in the trash provided
before you leave the lab with your class. This will make set up
for the next lab much easier. Also make sure the hand lenses, 2
nails per tray, and 1 brush per tray are returned to each tray.