Fossils Scholastic Science World

What is a fossil?

• Fossils give clues about organisms that lived

long ago. They help to show that evolution
has occurred.

• 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?

Multiple Select

What do fossils tell us?

• show that evolution has occurred

• what past environments may have been like

• how Earth’s surface has changed over time

• how many dinosaurs there were

Multiple Choice

Fossils are important because they help us understand ____.

• the future

• ancient life

• modern technology

• weather patterns

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.

Reorder

HOW IS A FOSSIL FORMED?

• 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.

• 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.

• 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.

• Erosion from rain, rivers, and wind wears away the remaining rock layers. Eventually, erosion or people digging for fossils will expose the preserved remains.

1

2

3

4

• 1
• 2
• 3
• 4

FIVE MAIN TYPES OF FOSSILS

Petrified
Fossils

Molds and

Casts

Carbon
Films

Trace
Fossils

Preserved
Remains

• 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.

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.

Categorize

Options (8)

dinosaur

Categorize the fossil types.

Petrified Fossils

Molds and Casts

Preserved Remains

Trace Fossils

• 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.

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.

This dinosaur footprint was

found in Namibia, Africa.

Match

Match the type of preservation to the name.

• Tar

• Amber

• Ice

Stops the bones from decaying.

trapped in a tree’s sticky resin

frozen which preserves the organism

• Stops the bones from decaying.

• trapped in a tree’s sticky resin

• frozen which preserves the organism