2. Fossil: The remains, imprints or traces of
prehistoric organisms that are preserved
in rock.
Fossils are evidence of not only when
and where organisms once lived, but
also how they lived.
3. What is a fossil?
• Fossils give clues about organisms that lived
long ago.
• They also provide evidence about how Earth’s
surface has changed over time.
• Fossils help scientists understand what past
environments may have been like.
• A fossil is the preserved remains of a once-
living organism.
What do fossils tell us?
5. Fossils are rare because very “lucky”
conditions are needed to create them:
The dead organism
must be protected
from scavengers,
microorganisms
and the processes of
weathering (usually
this means the body
is quickly covered
by sediments)
6. HOW IS A FOSSIL FORMED?
1. Sediment
An animal is buried by
sediment, such as
volcanic ash or silt,
shortly after it dies.
Its bones are
protected from rotting
by the layer of
sediment.
4. Erosion
Erosion from rain,
rivers, and wind wears
away the remaining
rock layers. Eventually,
erosion or people
digging for fossils will
expose the preserved
remains.
2. Layers
More sediment layers
accumulate above the
animal’s remains, and
minerals, such as
silica (a compound of
silicon and oxygen),
slowly replace the
calcium phosphate in
the bones.
3. Movement
Movement of tectonic
plates, or giant rock
slabs that make up
Earth’s surface, lifts
up the sediments and
pushes the fossil
closer to the surface.
7. A fossil is more likely to form if the
organism had hard parts like bones,
shells or teeth.
8. Fossils are generally only found in
sedimentary rocks because the
heat/pressure involved in forming
igneous and metamorphic rocks
would destroy the organism.
9. FIVE MAIN TYPES OF FOSSILS
Petrified
Fossils
Molds and
Casts
Carbon
Films
Trace
Fossils
Preserved
Remains
10. 1. Permineralized (Petrified) Remains:
are hard and rock-like because the
original material has been replaced by
minerals
11. • The word “petrified” means
“turning into stone.”
• Petrified fossils form when
minerals replace all or part
of an organism.
• Water is full of dissolved
minerals. It seeps through
the layers of sediment to
reach the dead organism.
When the water evaporates,
only the hardened minerals
are left behind.
PETRIFIED FOSSILS
PETRIFIED FOSSIL
The Field Museum in Chicago
displays a fossil of a
Tyrannosaurus rex.
12. 2. Molds/Casts: An object gets buried, then
decays leaving behind a space called a
mold. The mold gets filled in by other
sediments which harden into rock and
forms a cast of the original object
13. MOLDS AND CASTS
• A mold forms when hard parts of an
organism are buried in sediment,
such as sand, silt, or clay.
• The hard parts completely dissolve
over time, leaving behind a hollow
area with the organism’s shape.
MOLD FOSSIL
This mold, or imprint, is of
an extinct mollusk called
an ammonite.
• A cast forms as the result of a mold.
• Water with dissolved minerals and
sediment fills the mold’s empty
spaces.
• Minerals and sediment that are left
in the mold make a cast.
• A cast is the opposite of its mold.
CAST FOSSIL
This ammonite cast was
discovered in the United
Kingdom.
15. 3. Carbon Films: are when the
organism gets pressed against a
hard object and leaves behind a
thin film of carbon residue (similar
to a fingerprint)
16. • All living things contain an
element called carbon.
• When an organism dies
and is buried in sediment,
the materials that make up
the organism break down.
• Eventually, only carbon
remains.
• The thin layer of carbon
left behind can show an
organism’s delicate parts,
like leaves on a plant.
CARBON FILMS
FERN FOSSIL
This carbon-film fossil of a
fern is more than
300 million years old.
17. 4. Trace Fossils: Tracks that have
been preserved in mud/clay (similar
to hand prints in cement)
18. TRACE FOSSILS
• Trace fossils show the
activities of organisms.
• An animal makes a footprint
when it steps in sand or mud.
• Over time the footprint is
buried in layers of sediment.
Then, the sediment becomes
solid rock.
FANCY FOOTWORK
This dinosaur footprint was
found in Namibia, Africa.
19. 5. Original or Preserved Remains:
The actual organism or part of it
has been preserved in amber, ice or
tar (usually very rare and
valuable)
20. Some organisms get preserved in or close to their
original states. Here are some ways that can happen.
PRESERVED REMAINS
Amber
An organism,
such as an insect,
is trapped in a
tree’s sticky resin
and dies. More
resin covers it,
sealing the insect
inside. It hardens
into amber.
Tar
An organism,
such as a
mammoth, is
trapped in a tar pit
and dies. The tar
soaks into its
bones and stops
the bones from
decaying.
Ice
An organism,
such as a woolly
mammoth, dies in
a very cold
region. Its body is
frozen in ice,
which preserves
the organism—
even its hair!
