Download What are fossils?

What are fossils?
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Key Vocabulary
Relative Dating
Principle of Superposition
Absolute Dating
Fossil
Imprint Fossil
Trace Fossil
Index Fossil
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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.
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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.
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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?