What are fossils?

Key Vocabulary

Relative Dating

Principle of Superposition

Absolute Dating

Fossil

Imprint Fossil

Trace Fossil

Index Fossil

Key Vocabulary

Mold

Cast

Petrification

Fossils in Amber

Fossils in Tar

Frozen Fossils

Carbon Impressions

Relative Dating

Determining whether an object

or event is older or younger than

other objects or events.

“You are older than your baby

brother.”

Principle of Superposition

Younger rocks lie above older rocks in

undisturbed sequences. Scientists

can determine relative age of the rock.

Absolute Dating

Process of establishing the age of

an object by determining the

number of years it has existed.

(Radiometric dating – carbon 14.)

“You are 5 years old.”

My age!!

My birthday is May 6, 1957.

Give an example of my relative age.

Give an example of my absolute age.

Molds

A mold is a cavity in the ground

or rock where a plant or animal

was buried.

Casts

If the cavity is filled in

with sediment and

becomes a rock, it is

a cast. The cast

shows what the

outside of the

organism looked

like.

Trace Fossil

Any naturally

preserved

evidence of an

animal’s

activity. Tracks

of animals

found in rock

are examples of

trace fossils.

Petrification

A plant or animal’s tissues are

completely replaced by minerals.

Petrified pumpkins and a

petrified log.

Fossils in Amber

Some of the best insect fossils have been found in amber. Amber is hardened tree sap.

Fossils in Tar Tar pits were once covered with water.

Animals, who may have hunted in the

water or walked into the water were

stuck. The La Brea tar pits in California

are one of the most well-known.

Frozen Fossils Paleontologists rarely find such perfect specimens

from the past as this baby mammoth, discovered frozen in an excavation site of northeastern Siberia in 1977. Sometimes an animal would fall between huge pieces of ice in a glacier and could not escape. The animal would freeze and remain preserved in ice until the glacier thawed.

Carbon Impressions Carbon

impressions of plants can form when leaves are buried in sediment. As the plant decays, a thin film of carbon is left behind.

Why study fossils?

Fossils show the many kinds of

organisms that lived at different

times in Earth’s history.

Why study fossils?

Animal bones, teeth, and shells

give clues to past life.

Animal tracks help explain how

animals moved. It can also show

whether they traveled alone or in

packs.

Some of the oldest known fossils

are worm burrows.

Why study fossils?

Fossils show how

animals have

changed over time.

Example: Early

horse fossils show

that the horse once

was the size of a

small dog and had

four toes!!

Why study fossils? Fossils show that

Earth’s climate and

surface have

changed over time.

Example: Fossils of

ferns in Antarctica.

Fossils of ocean

animals in the

Andes Mountains

in South America.

Do you remember? • What is the difference between absolute

and relative dating?

• Which type of fossil is formed from tree

sap?

• Which type of fossil is formed when

minerals replace the tissue in an

organism?

• Name two reasons scientists study

fossils?