The Young Scientist Program
http://ysp.wustl.edu
Washington University School of Medicine
Fossil Formation
For YSP Volunteers: How to Run this Activity
Logistics
Number of Volunteers: 2-3
Set-up: 10 minutes – Separate out 1 red, 1 green and 1 yellow gummy bears for each
group. Fill 1 small cup with salt, 1 with soil, and 1 with sand for each group.
Approximate Running Time: 30 minutes
Module Overview
Students will learn about the Law of Superposition and create their own stratigraphic
columns using sand, salt, soil, and gummy bears. They will use what they learn from this activity to
interpret fossil evidence from the horse and its ancestors. There are 2 different worksheets for
different level students (the first recommended for elementary – early middle school, the second for
late middle school – high school).
Curriculum Links
Missouri Science Standards
4.3.A Evidence for the nature and rates of evolution can be found in anatomical and
molecular characteristics of organisms and in the fossil record. Interpret fossil evidence to
explain the relatedness of organisms using the principles of superposition and fossil correlation.
Evaluate the evidence that supports the theory of biological evolution (fossil records).
5.2.D Changes in the earth over time can be inferred through rock and fossil evidence. Use
evidence from relative and real dating techniques to infer geologic history.
Next Generation Science Standards
3LS4.A Evidence of common ancestry and diversity (3LS4-1).
4ESS1.C The history of planet Earth (4ESS1-1).
MS-LS4A Evidence of common ancestry and diversity (MS-LS4-1, MS-LS4-2).
MS-ESS1C The history of planet Earth (MS-ESS1-4).
Goals
1. To use the Law of Superposition to understand how geologic history can be inferred from
rock layers and fossils.
2. To use the Law of Superposition to interpret fossil evidence and the evolution of the horse.
3. To understand how fossil evidence supports the theory of biological evolution.
Materials
Large clear cups with labeled increments (A - F), gummy bears, small cups, different
colored “rock layers” (salt, soil, sand).
What to Expect
Based on past experience running this activity, you can expect…
The Young Scientist Program
http://ysp.wustl.edu
Washington University School of Medicine
Fossil Formation
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For older students, the "older gummy bears on bottom vs. younger near the surface"
concept will be intuitive and pretty easy.
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For older students, you may get questions about formations of rocks and their types,
plate tectonics, and facts about the fossil record. Be prepared to go into depth about
these things to make this activity more interesting for older students!
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Be prepared to answer questions about gaps in the fossil record, since that is a common
counter argument against the theory of evolution.
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"In preparing for battle I have always found that plans are useless, but planning is
indispensable.” - D. Eisenhower
Discussion Questions ANSWER KEY
a) Which bear is the oldest fossil? The youngest?
red is the oldest, yellow is the youngest
b) In general, where do you expect to find the oldest fossils in
the world? In the oldest (deepest) layers of rock.
c) How do your results support the Law of Superposition?
The newest layers of “rock” that we added were placed on top of the older layers of “rock”, like the Law of
Superposition states for natural systems.
d) In the image to the right, which animal do you think was found lowest in the stratigraphic column? Why?
Eohippus- it is the oldest ancestor of the horse and would be found in the oldest layers of rock, which would
be the lowest in the stratigraphic column.
e) How do these horse fossils support evolution? The fossils show a progression through time, in which the
horse evolved from the Eohippus ancestor. Each individual ancestor/fossil shows what changes occurred to
make the horse that we know today.
f) What would it mean if the Mesohippus fossil were found in multiple layers of rock?
This would mean that this animal lived, relatively unchanged, for a long time.
g) Would you be able to tell the exact age of a fossil if you only knew where it was found in the stratigraphic
column?
No, using the Law of Superposition and stratigraphic layering is only a relative dating technique. Absolute
dating techniques include radiometric dating, luminescence dating, and amino acid dating.
h) If there is more of one type of animal fossilized, does that mean that they were more populous in the
world at that time?
Not necessarily. It just means that this animal was subjected to the very specific conditions of fossilization
more often than other animals.
The Young Scientist Program
http://ysp.wustl.edu
Washington University School of Medicine
Fossil Formation
There are different processes of fossilization depending on the tissue type and external conditions.
Common types include casts and molds (a cast is when the organism is destroyed but leaves an impression
in the rock it was smashed in to, a mold is when this impression is filled with other materials), and
permineralization.
The process of permineralization: Animal gets buried—Covered in mud, which dries out quickly (If covered
in too wet of mud or water, it decomposes entirely). After tens of thousands of years, with the pressure
applied by the coverage, the minerals supplant the organic material. This has to happen very slowly, under
the exactly right conditions—low moisture (just enough to carry minerals into the tissue, but not enough to
support bacterial growth). Depending on the type of mineral and the rate of change, the fossils can be
extremely accurate, down to cellular structure. This takes a long time--Mastodon teeth, up to 12,000 years
old are still only partially permineralized.
Such exact conditions needed for fossilization helps to explain gaps in the fossil record.
i) What are some ways in which using stratigraphic columns for relative dating would be complicated?
If the rocks were formed on a slope, if molten rock works its way into existing rock and squeezed in between
layers of older rock, if a geologic folding event occurs (when a stack of originally horizontal rock gets
pushed up into a bent or curved deformation, often due to being in a shear zone or a fault), and fault zones
in general (faults are fractures in rock accompanied with significant displacement as a result of earth
movement-- large faults within the Earth's crust result from the action of plate tectonic forces, with the
largest being the boundaries between plates).
j) Why do different geological eras feature different sands/rocks/minerals?
Climate and catastrophe: oxygen & carbon dioxide concentration, temperature, plate movement, asteroid
impact, volcano activities, etc. can influence the features of rocks.
Pressure underground: deeper layer suffers higher pressure.
Organisms' activities: for example, fern & coal, stromatolite & ancient cyanobacteria.
Other reasonable answers also acceptable.
k) Does a thicker layer necessarily suggest longer time? No. 1) Deeper layers suffer much larger pressure,
which sometimes makes them thinner and denser. A deep thinner layer might sometimes represent a longer
geological time than a shallow thicker layer. 2) Some rocks and minerals are more resistant to pressure
than others. 3) Some geological eras are with fewer sediments, and even the 'land' and 'sea' sediments in
the same era can have different thickness. Other reasonable answers are also acceptable. P.S.1 If you are
not sure whether students' answer is right or wrong, just say 'it sounds plausible, but you should go to the
library or Internet to confirm it'. P.S.2 You may introduce isotopic dating methods here, and if necessary,
also Global Boundary Stratotype Section and Point (GSSP).