Fossils as Evidence for Change: (2+ to 3+ Day Lesson)
Day One:
Focus Question/Purpose: What is the geologic evidence for life
changing on earth (Standard 7.4d). (Students will explore the different
types of fossils, and be able to describe how they are formed).
Opening (Engaging Students in Learning and Tapping Into Prior
Knowledge-Superposition and Relative Dating): Via a journal prompt
followed by an informal class discussion, ask students to imagine that they
have not picked up their room since kindergarten. After 7+ years, they
finally decide to sort through the 2m of ‘stuff’ on their floor. Suggested
questions:
“What might you find on the top of the pile?
“In the middle?”
“On the bottom?”
“Where might you expect to find a finger painting?”
“Where might you expect to find ‘long-division’ homework sheets?”
“How does the great depth of the sedimentary layers of the Grand
Canyon relate to this?”
(Time: 5-10 minutes)
Deeper Exploration (Engaging students, accessing prior knowledge,
independent writing...): Journal Entry: Look at the sample fossils on
your table. Take one and describe 3 apparent features/characteristics about
it. Make a sketch of the fossil. Repeat this with two other fossils.
Hypothesize:
What is a fossil? How was each of these fossils formed? How are these
fossils dated? (We covered Relative and Radioactive Dating the Week
prior)
(1-2 sentences each) (10-15 minutes)
Option A
Have students form groups of 3-5 students to research their
individual fossil type using textbooks and/or computer resources.
Groups will present what they have discovered about their fossil type.
(10-20 minutes for research, 30 minutes for presentation)
Option B
Have students form groups of 3-5 students to research their
individual fossil type using textbooks and/or computer resources.
Groups will present what they have discovered about their fossil type.
(10-20 minutes for research, 30 minutes for presentation)
PowerPoint on How Fossils are Formed
Revisit three fossil samples and revise your original hypothesis.
(15-20 minutes)
Modifications for ELL/Special Needs Students: These students will be
given a copy of the PowerPoint presentation with certain key points
missing (blanked for the student to fill in during the slide show).
Option C
PowerPoint on How Fossils are Formed
Revisit three fossil samples and revise your original hypothesis.
(15-20 minutes)
Day Two
Review the concepts from day one: Fossil Types and Formation
Extension Activity: Hands-on Experiences
Simulation of a Mold and Cast Fossil
Lab-Mold and Cast Fossil
Background:
Fossils are remains or traces of dead organisms. Fossils help scientists learn about
living things that existed in the past. Many fossils are shells and bones that settle
into sand or mud. Over the years the sand or mud turned into rock
(permineralization/replacement). If the original shell or bone is dissolved away from
its surrounding rock, the hollow impression is called a mold. If the mold is later
filled with mineral matter, a cast is formed. The cast is a copy of the original shell or
bone.
Materials:
Shells/Plastic Fossil Specimen
Plastic Bowl
Sheetrock Mud/Plaster of Paris
Petroleum Jelly
Water
Procedure:
Check off each step as you complete it.
Cup
Stir Stick
Part A:
___ 1. Working with one partner, cover the ‘fossil’ object with a layer of petroleum
jelly.
___ 2. Slowly mix water with the powdered sheetrock mud (or Plaster of Paris)
until the mixture is the consistency of toothpaste (not so thin that it ‘pours’
out of the cup, but almost to that point).
___ 3. Scoop the liquid plaster into the plastic bowl.
___ 4. Place the object on the surface of the liquid plaster. Let the plaster dry for
at least twenty minutes.
___ 5. Remove the object and clean it. Its impression in the plaster is called the
mold.
___ 6. Clean up and let the mold dry and completely harden.
Part B:
___ 1. Coat the entire top layer of the mold with petroleum jelly.
___ 2. Prepare more liquid plaster (as done in Part A).
___ 3. Pour the plaster over the impression in the dried plaster, filling it to about
1/4” above the top of the impression.
___ 4. Let the new plaster dry overnight.
Day 2, Part C:
1. After the plaster is thoroughly dry, separate the two plaster blocks. The dried
plaster on the top is the cast, while the ‘hollowed-space’ piece was the mold.
2. Compare the mold, the cast, and the original object.
Discussion Questions:
1. Which of the plastered objects is most like the original object?
2. How does the mold object differ from the original object?
3. In the activity, what corresponds to the soft mud or layer of soil?
4. Which of these objects represents the mold. How might the mold be created in
nature?
5. Which of these objects represents the cast? How might the cast be created in
nature?
Other Hands-on Experiences:
Other simulation models might include making other types of fossils. For example:
Insect in Amber model involves using clear Elmer’s glue (hardens in two days), or
actual rosin (melts on a hot plate and cools within a couple of hours. Students can
imbed real bugs, rubber bugs, leaves, etc…
The ‘Lost Wax’ Experiment better simulates a mold and cast fossil with
permineralization. Refer to PowerPoint.
Culminating Assessment:
Set up a practical lab with samples of the various types of fossils. In lieu of actual
fossil samples, you could use photos. For each sample/photo, have students list the
type of fossil it is (mold, cast, carbon copy, impression, petrified remains, actual
remains, insect in amber, etc…) and how it was probably formed.