|
 |
|
|
| Overview |
| Grade Level: 7-9 |
| Background Information:
The geologic timescale is based on the history of life on our planet.
Eras, epochs, and periods all relate to the changes in Earth's biology.
Early geologists noticed that certain species, families, or even
phyla disappear completely or appear in the rock record. The most
famous example of this is the dinosaurs that appeared during the
Triassic and disappeared at the end of the Cretaceous. The era that
the dinosaurs existed in was the Mesozoic meaning middle life. After
the dinosaurs went extinct, mammals expanded and became the predominant
group of land animals. The time of the mammals is called the Cenozoic,
or new life.
Until recently, there was no way to determine how old the rock
units actually were. Thus determining the age of rocks was done
using relativity. For instance, dinosaurs came and went before large
mammals. This can be determined by studying the relationships between
rock units. Worldwide, rock units that bear dinosaur bones are underneath
those that bear mammal bones. According to the principle of superposition,
they must be older. Thus, a geologist finding two widely separated
rock units, one containing mammal bones and one containing dinosaur
bones, knows that the unit with dinosaurs is older than the one
with the mammals. This is called relative dating. It wasn't until
the discovery of radioactivity in rocks that geologists were able
to give rocks absolute ages (for example: dinosaurs went extinct
66 million years ago). Relative dating is cheaper and easier and
so is regularly used by geologists for most purposes.
Fossil range charts can show the length of time that various organisms
have been found in the fossil record. For instance, the range of
dinosaurs is from the beginning of the Triassic to the end of the
Cretaceous. This is usually represented in a bar graph form with
either the x or y axis representing time and the other axis representing
the fossil groups present. Geologists use the x-axis for time because
it correlates with our conception of time having a starting point
and marching towards our current position. The y-axis also works
in geology because rock units are vertically stacked. Thus older
times are placed at the bottom of the y-axis and time gets younger
as it marches up the y-axis. By determining which fossils are present
in a given rock sample, the relative age of the rock can be determined.
Using individual species, geologists can narrow down the age of
a rock, often to within a million years (a small amount of time
for geologists).
In this activity, students will use fossil range charts to help
them understand the concept of relative dating. An optional teacher-directed
activity will help students learn about fossil range charts. Then
they will graph a range chart for ammonites, a marine group of organisms
that looked like nautilus's and went extinct at the same time as
the dinosaurs. They will then use the range chart to determine the
geologic age for several 'rocks' and will determine which rocks
will be most useful for oil companies looking to drill for oil.
Acknowledgement
Thanks to Dr Tim Palmer C.Geol., F.G.S., Executive Officer, The
Palaeontological Association for his help with the palaeontological
information for this activity.
|
| Content Standards |
| Related National Standards:
This lesson addresses the following National Content Standards
found at: http://books.nap.edu/html/nses
Content Standard C: As a result of their activities in grades
5-8, all students should develop understanding of:
- Diversity and Adaptations of Organisms
- Extinction of a species occurs when the environment changes
and the adaptive characteristics of a species are insufficient
to allow its survival. Fossils indicate that many organisms
that lived long ago are extinct. Extinction of species is
common; most of the species that have lived on the earth
no longer exist.
|
Content Standard C: As a result of their activities in grades
9-12, all students should develop understanding of:
- Biological Evolution
- Species evolve over time. Evolution is the consequence
of the interactions of (1) the potential for a species
to increase its numbers, (2) The genetic variability
of offspring due to mutation and recombination of genes,
(3) a finite supply of the resources required for life,
and (4) the ensuing selection by the environment of
those offspring better able to survive and leave offspring.
- Natural Selection and its evolutionary consequences
provide a scientific explanation for the fossil record
of ancient life forms.
|
Content Standard D: As a result of their activities in grades
5-8, all students should develop understanding of:
- Earth's history
- Fossils provide important evidence of how life and
environmental conditions have changed.
|
Content Standard D: As a result of their activities in grades
9-12, all students should develop understanding of:
- The Origin and Evolution of the Earth System
- Geologic time can be estimated by observing rock sequences
and using fossils to correlate the sequences at various
locations. Current methods include using the known decay
rates of radioactive isotopes present in rocks to measure
the time the rock was formed.
|
|
| Extension Web Sites
from PBS: |
|
A
Science Odyssey- The Dating Game
Use this website for a lesson on absolute dating using radioactive
elements.
Newtons
Apple- Dinosaur 1
Newtons
Apple- Dinosaur 2
These sites contain a variety of activities related to dinosaur
fossils.
Nova
Teachers Guide-The Curse of T. Rex
This Nova program will allow students to see a real paleontological
dig and to consider ethical and moral implications of commercial
fossil collecting.
|
| Activity 1: I Always Knew My
Teacher Was a Dinosaur! |
| Time Allotted:
20 minutes
Materials:
Overhead transparency or poster prepared as described below
| Objectives: |
- Students will learn to read fossil range charts.
- Students will develop an understanding of the strengths
and weaknesses of the fossil record.
- Students will become familiar with the concepts index
fossil and fossil range.
|
Before watching the first video, introduce the concepts of relative
dating vs. absolute dating (see background above).
Watch the AFG Video Segment:
 |
Fossil
Museum
Eons
ago, what is now Indiana was under the sea, which is why today
thousands of fossils of ancient sea life can be found at the
Falls of the Ohio. |
|
Note: Video starts at 'More than 300 million years ago.'
Stop after hearing 'Indiana was once located in the tropics'.
|
| Discussion Questions for Video Segment: |
- Describe some information that fossils can give about
the past.
- What examples of relative ages did you hear? Absolute
age?
|
| Teacher Instructions: |
- Make your own 'fossil' range-chart to illustrate how they
work to your students! I have done this activity using different
groups of people such as basketball players from the University
of North Carolina Basketball team and teachers from my school.
Any population that your students knows fairly well will
work.
- Choose a group of people, for example, teachers in your
school. You will want about 10 individuals, some of who
have been around for a long time and some of whom only were
there for one or two years. Make a bar graph with time on
the X-axis and teachers names on the Y-axis. Shade the years
that correspond with each teacher's tenure at the school.
Now make your graph into an overhead (or into a power point
slide) to share with the class.
- Tell students to imagine that there has been a fire in
the library (or that a mouse has munched on the yearbooks
or some other calamity has occurred). The librarian is trying
to reconstruct what's left of the yearbooks and has come
upon a pile of pages with photographs on them. Show the
students your range chart. Have them describe what they
can tell by looking at it.
Note: A sample of the range chart used in this activity is
available in the PDF version of
this lesson plan.
|
| Discussion Questions: |
- If you find a photo that has Mr. X, Ms Y, and Mrs. Z in
it, what year is it from? How do you know? (Be sure that
X, Y, and Z were all there together for only one year. This
question illustrates the idea of overlapping ranges.)
- If you find a photo that has Mr. X, Ms Y, and Miss Q.,
what year is it from? How do you know? (Assuming Miss Q.
has been there for only a year or so, this question illustrates
the idea of an index fossil)
- If you find a photo that has Mr. X, Ms Y, but not Mrs.
Z in it, what year is it from? Does the fact that Mrs. Z
is missing mean anything? (no, not all fossils are found
in all rocks.)
- Teachers: my charts usually end up having more index fossils
toward the recent end of the chart because I wasn't around
20 years ago and the people who were don't remember the
short-timers. If yours came out the same way, ask the students
why they think that happened. Help them discuss that the
fossil record is similar. Short-lived species that didn't
preserve well or that existed only in small regions often
aren't fossilized in large numbers (if at all) and therefore
are overlooked by paleontologists. Thus the life appears
more diverse in more recent epochs leading to the concept
of an evolutionary tree, but this is merely an artifact
of preservation.
|
|
| Activity 2: Oil Exploration
and Fossil Ranges |
| Time Allotted:
45 minutes (can be completed as homework)
Materials:
Copies of the student directions
Optional: fossils, particularly fossil ammonites, belemnites, orthocones,
or nautilus
| Objectives: |
- Students will learn to use bar graphs to plot fossil ranges.
- Students will develop an understanding of 'relative time'
using fossil range charts.
- Students will use fossil range charts to understand how
a rock can be dated using the geologic timescale.
- Students will use fossil range charts to predict where
oil might be found.
|
Watch
the AFG Video Segment:
|
Iowa's
Geology - Fossils, Sediments and Loess
Iowa's
geological history can be traced back through the layers in
the earth. |
|
Note: Video starts at 'The interesting sequence of sedimentary
rocks…' Stop after hearing 'all hidden by layers of clay and
topsoil'.
|
| Discussion Questions for Video Segment: |
- Describe some information that fossils can give about
the past.
- What examples of relative ages did you hear? Absolute
age?
|
Teacher Instructions
Have students complete
Activity 2 (see student directions)
Assessment
A sample fossil range chart for this activity and answers to the
data analysis questions is available in the PDF version of this
lesson plan.
Watch the AFG Video Segment:
|
Iowa's
Diverse Fossils
A
variety of fossils from both ancient forests and marine origins
can be found near Iowa's coal deposits. |
|
Note: Video starts at 'As the DesMoines flows in its southeasterly
course…' Stop after hearing 'Iowa was much closer to the equator.'
|
| Discussion Questions for Video Segment: |
- What was the environment like in a coal swamp?
- In what way is coal formation different from oil formation?
Similar? (see student handout for a brief description of
oil formation).
- Would the fossil range chart you made today be useful
in dating coal deposits?
- Could a fossil range chart be useful in dating coal deposits?
What would it include?
|
|
|
 |
 |
