4-1 Fossils

Earth’s History – Course 2

My Planet Diary pg. 140A Dinosaur Named Sue

On a hot day in August 1990, Sue Hendrickson was hunting for fossils near the town of Faith, South Dakota. She found some little pieces of bone below a cliff. When she looked up at the cliff, she saw more bones. These bones weren’t little. They were enormous! She and other scientists determined that they were the bones of a Tyrannosaurus rex. In fact, she’d found the largest and most complete skeleton of a Tyrannosaurus ever discovered. Today, the skeleton, nicknamed “Sue,” is on display at the Field Museum in Chicago.

1.What science skills did Sue Hendrickson use when she discovered Sue ? __________________________________________________

2. What do you think scientists can learn by studying dinosaur skeletons?

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What are Fossils? Pg. 141

Fossils are preserved remains or traces of living things.

Most fossils form when living things die and are buried by sediment. The sediment slowly hardens into rock and preserves the shapes of the organisms.

Sediment is made up of rock particles or the remains of living things.

How a Fossil Forms: A fossil may form when sediment quickly covers an organism’s body.

Assess Your Understanding pg. 141

I get it! Now I know that fossils are _______________________

___________________________________________________

What are the Kinds of Fossils? Pg. 142

molds and casts: A mold is a hollow area in sediment in the shape of an organism or part of an organism. A cast is a solid copy of the shape of an organism.

petrified fossils: minerals have replaced part or all of an organism.

Fossils found in rock include:

trace fossils: such as footprints provide evidence of the activities of ancient organisms.

carbon films: an extremely thin coating of carbon on a fossil that preserves the delicate parts of plant leaves and insects.

Preserved Remains: when the remains of organisms are preserved in substances such as tar, amber, or ice.

HOW IS A FOSSIL FORMED?

1. SedimentAn 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. ErosionErosion from rain,

rivers, and wind wears away the remaining rock

layers. Eventually, erosion or people

digging for fossils will expose the

preserved remains.

2. LayersMore 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. MovementMovement 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.

FIVE MAIN TYPES OF FOSSILS

PetrifiedFossils

Molds andCasts

CarbonFilms

TraceFossils

PreservedRemains

• 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 FOSSILThe 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 FOSSILThis 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 FOSSILThis ammonite cast was discovered in the United

Kingdom.

• 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 FOSSILThis carbon-film fossil of a

fern is more than300 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.FANCY FOOTWORK

This dinosaur footprint was found in Namibia, Africa.

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!

Video: Becoming a Fossilhttp://www.pbs.org/wgbh/evolution/library/04/3/l_043_01.html

PBS

Article: Major Fossil Findhttp://www2.scholastic.com/browse/article.jsp?

id=3751945Scholastic News Online

Online Exhibit: Fossil Hallshttp://www.amnh.org/exhibitions/permanent/fossilhalls

American Museum of Natural History

Interactive Game: Fossil Hunthttp://channel.nationalgeographic.com/episode/dino-

death-trap-2998#tab-fossil-huntNational Geographic

For more on fossils visit:

Scholastic Classroom Magazines. www.scholastic.com Photo Credits: PAGE 1: UTAH MUSEUM OF NATURAL HISTORY (DINOSAUR); PHOTOTAKE INC./ALAMY (ANT). PAGE 3: 5W INFORGRAPHIC (GRAPHIC). PAGE 4: Jason Lindsey/Alamy (DINOSAUR); Peter Bowater/Alamy (MOLD); David Lyons/Alamy (FERN); Hoberman Collection UK/Alamy (FOOTPRINT); John Cancalosi/Alamy (MANTIS). PAGE 5: Gary Crabbe/Alamy (DINOSAUR). PAGE 6: Peter Bowater/Alamy (MOLD); Detail Heritage/Alamy (CAST). PAGE 7: David Lyons/Alamy (FERN). PAGE 8: Hoberman

Collection UK/Alamy (FOOTPRINT). PAGE 9: John Cancalosi/Alamy (MANTIS); R1/Alamy (TAR PITS); Gianni Dagli Orti/Corbis (MAMMOTH).

Assess Your Understanding pg. 143

1a. Identify A (mold / trace fossil) can form when sediment buries the hard part of an organism.

b. Explain A petrified fossil forms when _________________ replace parts of a(n) _________________________.

c. Make Generalizations What might you learn from a carbon film that you could not learn from a cast?

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I get it! Now I know that the kinds of fossils are ______________

___________________________________________________

What Do Fossils Show? Pg. 144

A paleontologist is a scientist who studies fossils.

The fossil record is the combined information about fossils collected by scientists throughout history.•It provides evidence about the history of life and past environments on Earth.• It also shows how different groups of organisms have changed over time.

The term evolution is used to identify the process of gradual change in living things over long periods.

A type of organism is extinct if it no longer exists and will never again live on Earth.

Wyoming, 50 Million Years AgoToday, Wyoming has areas of dry plateaus, but 50 million years ago it was very different. Infer- Identify the organism or kind of organism shown by fossils a, b, and c.

Challenge What features of Hyracotherium show that it is related to horses?

Fossils – Figure 3 pg. 144

Assess Your Understanding pg. 145

2a. Explain What does the fossil record show about how life has changed over time? ___________________________________

___________________________________________________

b. Apply Concepts Give an example of a question you could ask about a fossil of an extinct organism. _____________________

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I get it! Now I know that the fossil record shows _____________

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