Transcript A Trip Through Geologic Time

Good Morning!
 1. Complete your warm-up: What happens at a
convergent boundary? Be specific.
 2. Have out your Venn Diagram. You may have it
pasted in your notebook, I am coming around to check
for completion.
 3. Copy tonight’s HW: Matching half sheet
 4. Read silently.
10 minutes to finish your chart.
A Trip Through Geologic Time
 NOTE: Under “Kinds Of Fossils” you need to ADD
Trace Fossil.
Fossils
 Fossils are traces or
remains of ancient
life.
 Fossils show how
life has changed
over time.
 Scientists who study
fossils are
paleontologists.
Fossils
Fossils are
usually
found in
sedimentary
rocks.
Kinds of Fossils
Petrified Wood:
stone fossil of
a tree.
Kinds of
Fossils
 Molds and
Casts
 Mold: is a
hollow area in
the shape of
an organism.
 Cast: is a copy
of the shape of
an organism.

Carbon Films:
an extremely
thin coating of
carbon on rock;
shows the soft
parts of the
organism.
 Trace Fossils:
evidence of the
activities of ancient
life. Ex: footprints,
animal trails, feces,
or animal burrows.
Kinds of Fossils
Kinds of Fossils
 Original
Remains actual
body parts of
an organism.
May form in
ice (best
preserver),
amber (sap),
or tar.
Why Study Fossils?
1. To learn what past
life forms were like.
2. To classify organisms
in the order in
which they lived.
3. All the fossils found
on earth make up
the fossil record.
Fossil Record
 Provides evidence
about the history
of life on Earth.
 Shows how
different groups
of organisms have
changed or
evolved; while
others became
extinct.
The fossil
record is
incomplete;
most
organisms do
not become
fossils.
Remember!
Other evidence show change
in life and the environment
 Tree Rings- show weather patterns
 Ice Cores- show how the atmosphere has
changed over time
Finding the Age of Rocks Through
Rock Dating
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Ages of Rocks
 The relative age of
a rock is its age
compared to other
rocks.
Use words like:
“older or younger”
 The absolute age
of a rock is the
number of years
since the rock was
formed.
Ex: 358-360 mya
Rock Joke!!
What does a rock want
to be when it grows up?
A Rock Star!!
 It can be difficult to
determine a rocks absolute
age. So… scientists use the
law of superposition.
 According to the law
of superposition,
in horizontal
sedimentary rock
layers the oldest
layer is at the
bottom. Each higher
layer is younger than
the layers below it.
The Position of
Rock Layers
Rock Joke!!
How do rocks wash
their clothes?
The Rock Cycle!!
Other Clues to
Relative Age
 Clues From Igneous
Rock
 Lava that cools at the
surface is called an
extrusion. Rock below
an extrusion is always
older.
 Magma that cools
beneath the surface is
called an intrusion. An
intrusion is always
younger than the rock
layers around and
beneath it.
Other Clues to Relative Age
 Faults (a break in
the rock) are always
younger than the
rock it cuts through!
 Unconformities:
An unconformity is a
gap in the geological
record. New rock
forms on top of
eroded rock
Using Fossils to Date Rocks!
 Scientists use index
fossils to match rock
layers.
 An index fossil must
be widely distributed
and represent a type of
organism that existed
only briefly.
 They tell us relative age
of the rocks
The Trilobite
 One example of an index
fossil is a trilobite.
 Trilobites were a group of
hard-shelled animals
whose bodies had three
distinct parts.
 They evolved in shallow
seas more than 500
million years ago.
Fossil Study Guide