FOSSILS
Clues to Earth’s Past Creatures
and Environment
SC Standard 8-2.2
Summarize how scientists study
Earth’s past environment and
diverse life forms by examining
different types of fossils.
What is a fossil?
• A fossil is the
preserved remains
or traces of an
organism that lived
in the past
• Usually fossils are
more than 10,000
years old
http://www.youtube.com/watch?v=3rkGu0BItKM
What do fossils tell us about
Earth’s past?
• Fossils are clues
to:
– The diversity of
living things
throughout Earth’s
history
– Past climate and
surface changes
– Changes that have
occurred with
organisms over time
Who studies fossils?
• Paleontology is the
study of fossils
• Scientists who
study fossils are
called
paleontologists
How are fossils classified?
• Fossils are
classified by how
they are formed
• Types of fossils:
–
–
–
–
–
–
Mold fossil
Cast fossil
Petrified fossil
Preserved fossil
Carbonized fossil
Trace fossil
Mold Fossil
• Forms when:
– Sediments bury an
organism
– Sediments change
into rock by
pressure
– The organism
decays
– Leaves a cavity or
hollow in the shape
of the organism
Cast Fossil
• Forms when:
– A mold is filled with
sand or mud
– Sediments harden
into the shape of
the organism
Mold and Cast Fossils
• Most common form of
fossils
• Most fossils form
when sediment buries
a dead organism
• Organism most likely
lived in or near quiet
water (swamp, lake,
shallow sea)
Petrified Fossil
• Also called
permineralized
fossil
• Forms when:
– Minerals from
groundwater soak
into the buried
remains of
organisms
– Minerals replace
the organic remains
– Changes into rock
Preserved Fossil
• Forms when:
– Entire organisms or
parts of organisms
are prevented from
decaying
– Trapped in rock,
ice, tar, or amber
Carbonized Fossils
• Form when:
– Organisms or parts
are pressed
between layers of
soft mud or clay
– Mud or clay hardens
– Squeezes almost all
the decaying
organism away
– Leaves the carbon
imprint in the rock
Trace Fossils
• Forms when:
– Mud or sand
hardens to stone
where a footprint,
trail, or burrow of
an organism was
left behind
Dino Tracks
The Fossil Record
• Millions of fossils have been collected
and studied from all over the world
• Provides evidence of the history of
life on Earth
• Shows that different groups of
organisms have changed over time
http://www.abc.net.au/beasts/fossilfun/burial/default.htm
Check for Understanding
Test Your Skills
Which of the following
is least likely to be
found as a fossil?
a.
b.
c.
d.
Clam shell
Shark tooth
Dinosaur bone
Jellyfish imprint
Test Your Skills
Fossils are usually
found in _______?
a.
b.
c.
d.
Desert land
Mud
Sedimentary rock
Rocks formed inside
volcanoes
Test Your Skills
Fossils of animals
found in the La
Brea tar pits are
examples of what
kind of fossils?
a.
b.
c.
d.
Carbon film
Mold fossil
Preserved remains
Petrified fossil
Test Your Skills
Marine fossils have been found in
exposed rock layers in South
Carolina. Which of the following
is the best interpretation of this
discovery?
A. Marine organisms evolved from
land-dwelling organisms.
B. Parts of South Carolina were
once covered by water.
C. These organisms could live both
in water and on land.
D. They were carried by humans to
South Carolina.
Test Your Skills
Select the correct letter for the choices that
are all definitely fossils.
A.
B.
C.
D.
Egyptian Mummy, Ancient Pottery, Worm
burrows in sandstone
Imprints of rain drops, Trilobite shells,
Mud cracks
Dinosaur tracks, Mammoth found in ice,
Seashells found in limestone
Stone Age tools, Giant shark teeth,
Seashells found on a beach
Test Your Skills
Using the choices below,
identify the fossils formed
by petrification.
A. Dinosaur tracks, Black
outline of a plant leaf
B. Rock-like wood, Rock-like
Brachiopod shell
C. Mud-filled shape of a
gastropod shell, Mammoth
droppings
D. Insect in amber, Hollow
cavity shaped like a trilobite
Do Now
1. What is sea-floor spreading?
2. How are mold and cast fossils related?