October 2006
Naomi J. Marty
GK-12 Program
Who Was Here First? – A Relative Dating Activity
Concept:
Earth Science: Determining Geologic Time / Fossil Records
Description of Activity:
Students practice sequencing cards that represent different rock layers based first on
alphabetical characters that they contain and second on fossil pictures they contain.
This activity was found at the following awesome website, by Marsha Barber and Diana
Scheidle Bartos:
http://www.ucmp.berkeley.edu/fosrec/index.html
State Standards:
(arkedu.state.ar.us)
ESS.9.6.1
Research methods of determining geologic time:
 fossil records
 mountain building
 rock sequencing
ESS.9.6.2
Model rock layer sequencing based on characteristics of fossils
ESS.8.6.15
Investigate careers, scientists, and historical breakthroughs related to internal forces that change
the earth
Management Suggestions:
It may be beneficial to pair quick-learners with slower learners so that pairs of students
don’t get behind.
Materials:
o Card Sets A & B (shown below)
o Cut-out landmasses of Earth
-labeled with locations of several fossil finds
Procedure
1. Begin to discuss with the students how paleontologists, biologists, and geologists use the
fossil record to learn about the past history of the Earth. Start with a picture of T. rex on
the projector. Ask the students several questions. What did it eat? Why are its arms so
short? How did it die? How do we know? How do we learn about what no longer exists?
Tell the students that scientists have to use the steps of scientific inquiry to answer the
kinds of questions about the past. They have to examine the fossil record and use actual
data to put together pieces of evidence to answer questions about the past. They have
to look at the big picture, because things that were happening in T. rex’s environment
certainly affected his life. Fossils provide important evidence of how life and
environmental conditions have changed. Discuss how we have to look at the evolution
not just of life over time, but of the Earth itself over time. We cannot study Biology
without including Evolution or Ecology, nor can we study Evolution without understanding
Tectonics and Energy. These major concepts cannot be understood in without each
other.
2. Millions and billions of years is difficult to comprehend, but scientists use ‘relative’ dating of
time to help sort that out. Tell the students they are going to do a sequencing activity
with letters. When they can sequence the letters, they will be given a set of rock layer
cards with different fossil types printed on them, which they will sequence as well.
Sequencing rock layers is how paleontologists use fossils to give relative dates to
different layers of rock.
3. Give the students the attached handout with the Procedure Set A and card Set A. Have them
perform the activity and answer the questions at the end. In short, they will:
Spread the cards with the nonsense syllables on the table and determine the
correct sequence of the eight cards by comparing letters that are common to individual
cards and, therefore, overlap. The first card in the sequence has "Card 1, Set A" in the
lower left-hand corner and represents the bottom of the sequence. If the letters "T" and
"C" represent fossils in the oldest rock layer, they are the oldest fossils, or the first fossils
formed in the past for this sequence of rock layers.
The letters should be:
4.
Have the students proceed to Procedure Set B and card Set B. Have them perform the
activity and answer the questions at the end. In short, they will:
Carefully examine the second set of cards which have sketches of fossils on
them. Each card represents a particular rock layer with a collection of fossils that are
found in that particular rock stratum. All of the fossils represented would be found in
sedimentary rocks of marine origin. Figure 2-A gives some background information on
the individual fossils.
The oldest rock layer is marked with the letter "M" in the lower left-hand corner.
Find a rock layer that has at least one of the fossils you found in the oldest rock layer.
This rock layer would be younger as indicated by the appearance of new fossils in the
rock stratum. Keep in mind that extinction is forever. Once an organism disappears from
the sequence it cannot reappear later. Use this information to sequence the cards in a
vertical stack of fossils in rock strata. Arrange them from oldest to youngest with the
oldest layer on the bottom and the youngest on top.
The order should spell ORGANISM.
5.
Discuss the students’ answers to the questions. Which fossil organisms could possibly be
used as index or guide fossils? Name three organisms that probably could not be used
as index fossils and explain why. In what kinds of rocks might you find the fossils from
this activity? State the Law of Superposition and explain how this activity illustrates this
law.
6. Show students where certain fossils are found on the tips of landmasses and ask if they think
it is a coincidence that the fossils are found in those areas. If they don’t catch the idea
that the landmasses were together at one time, mention that these animals couldn’t have
possible survived a swim across the ocean. Ask what theory this supports (Theories of
Plate Tectonics and Continental Drift).
Figure 2-B. Stratigraphic Section for Set B
Set A
Set B
Reflection:
1. What worked?
This activity made the students really think and process the information that I was giving
them. They didn’t like that at first, but when they understood what they were supposed to be
doing, they seemed excited. I really liked this activity because it is a puzzle that they have to
figure out by interpreting data.
2. What didn’t work?
Most students really needed someone to walk through an example of sequencing before
they understood, so we ended up doing the first set of cards (Set A) together in the end so that
they could move on to the next set.
3. What would I change for the next time?
I think I would spend more time explaining the idea of sequencing. A powerpoint
presentation explaining how to sequence a series of layers would make this activity go so much
more smoothly.