Experimental Geology: It's more focused, and more useful, than you think
Russ Colson
Worlds of Change Workshop
MSUM Nov 8, 2010
Science is not something we know but rather something we do. Teaching only the information
of science is like teaching the rules of basketball and thinking we've taught how to play the
game. Unfortunately in Earth Science, "doing" is sometimes limited to such activities as
classification of rock types and testing minerals for hardness. While these are valid activities,
they do not do a good job of teaching key science concepts and are only tangentially related to
the kinds of thinking and learning that engage earth scientists.
While geology began as an observational science (much like biology), its history as an
experimental science goes back several centuries. Experiments place constraints on how things
happen on Earth, and thus give us improved insight into the story of the Earth. In the classroom,
experiments engage teachers and students, build relationships, and illustrate thinking in a way
that more traditional "learning activities", demonstrations, or worksheets don't allow.
Experiments are not disorganized "activities" or art projects in which illustrations of solar
systems, volcanoes, or storm systems are created. Nor are experiments merely "simulations" in
which students "try a bunch of stuff" and see what happens. In experiments, students control
variables, measure results, record data, and make interpretations. In Earth Science, experimental
results are often applied to telling some story of the Earth.
Experiments allow students to experiment. The key job of the teacher is to decide where to
provide guidance and where to let students explore. Too much guidance and the activity
becomes a cook-book exercise. The student learns how to follow directions but not much about
science. Too little guidance, and the activity becomes aimless and incomprehensible. Maybe
fun, but again not much science learning. Factors to consider in providing guidance are 1) age
and abilities of students 2) amount of time students will have to complete the project 3) which
problems you want students to solve and which answers you want to simply give them.
Things students might learn with a well-assigned experiment include:
1) Experience conceiving and designing an experiment (creativity). The teacher needs to
provide instruction or guidance on the specific goal and emphasize that students must change one
variable, find a way to measure the response of another variable, and keep all other variables
constant.
2) Experience observing and recording data (carefulness and precision). The teacher needs to
provide some level of guidance, for example, a data table, perhaps headings, how to record
repetitions of measurements. Sometimes hints of how to observe or measure are needed.
Sometimes more specific guidance is needed.
3) Experience graphing (analytical and abstract reasoning). Graphing is a key skill in science
which is intimately related to the thinking process scientists use in approaching problems. Most
graphing in Earth Science involves X-Y graphs, not bar graphs or pie charts, etc, although I have
sometimes used bar graphs for younger kids.
4) Experience interpreting results (either analytical or creative). The teacher usually needs to
provide a specific goal of the experiments which helps or guides in interpretation of the results.
The teacher should also be engaged in the experiments with the students, helping notice and
interpret. In my experience, there is always the opportunity for unexpected results that I also
need to figure out and interpret.
5) Experience applying the results to understanding of the earth (insight into the Earth and
insight into the fundamental process of science). I usually provide the application to the Earth,
either as a conceptual discussion or as a specific applied puzzle.
Here are a few example Earth Science experiments which can be adapted to students of many
ages by adjusting the amount or type of guidance given. I often change the guidance I give in
order to emphasize different aspects of the problem.
#1 Historical Geology: Experiments with stream transport and deposition
Russ Colson-MSUM
Historical Geology experiments are used to understand processes that happened in the past so
that we can better interpret the story a sedimentary rock tells us. How to read the story told by
sedimentary rocks is perhaps THE key idea of geology!
Example question to solve: Suppose that we find a Tricerotops bone in a conglomerate
deposited along an ancient river channel. If the particles of gravel are all bigger than about ½
inch, how steep was the river in which the gravel and bone were deposited?
Supplies: water, buckets to carry and pour water, gravel of different sizes, rulers, basins to catch
water, flume trays (I use drain spouts), blocks or other materials to prop up flume trays at
different angles.
Hint on experimental design: You want to complete of a graph of the sort shown below.
Steepness
of flume
(or river)
Zone of
erosion
Zone of
deposition
Size of gravel particles
bigger
Given the time that we have (about 35 minutes or so), do only 3 different sizes of gravel,
determining for a variety of steepnesses whether the particles are deposited (stay put) or eroded
(wash away).
See the following page for graph paper.
Variable you control (independent variable) =
Response variable (dependent variable) =
Variables you want to keep constant so they don't alter affects of the results =
Your answer to the Question:
How steep was the river in which the gravel and bone were deposited?
#2 Physical and Historical Geology: Experiments with Ice and Salt Water
Russ Colson-MSUM
Some experiments are used to understand a physical-chemical process in nature, which is then
used to predict something about a past process on Earth or another planet.
Example question to solve: Suppose that you find that the lava on the moon Europa is a mixture
of ice and salt in the proportions 10wt% salt and 90wt%H2O. Now, if the lava resulted from
partly melting salty ice at some shallow depth in the moon's crust what was the temperature of
that melting event?
Supplies: Ice, salt, balance, graduated cylinders, thermometers, and insulated containers for
doing experiments (I often use glass beakers, which, while not perfectly insulated, give
reasonable results. I have also used tin cans with "pop can insulators" around them.)
Hint on experimental design: A key discovery of this experiment, and a key concept in
understanding what it means, is that ice and salt water of a particular composition can coexist at
only a single temperature (at 1 atm pressure). Take measurements of the temperature of various
salt-water + ice mixture (make sure there is an over-abundance of ice, otherwise heat from the
room will overwhelm your experimental results). Then quickly pour off some of the salt water
(no ice or salt mixed in), let it warm to room temperature, and measure its density (density =
volume/mass--you can figure this one out). Compare the density to a calibration curve to get the
concentration of salt in weight% salt (a calibration curve is attached although you could
construct your own).
Because of our time constraints (about 35 minutes or so), I want you to do only 3 experiments,
one with no salt at all (ice + water), one that initially contains about 15wt% salt (the
concentration will change during the experiment because some of the ice will melt), and one that
initially contains about 23% salt).
Your goal is to quantify a graph of the type below (graph paper on the following page)
Temperature
Line showing temperatures where ice
can coexist with various concentrations
of salt water
Wt% Salt (0% on the left, 24% on the right)
NOTE: This experiment can also be used to help students understand why salt melts road ice but
yet can be used to make ice cream (sometimes we make homemade ice cream during lab--recipe
attached!) It is analogous to experiments in silicate lava on Earth (which are done at much
higher temperatures!)
NOTE: If you have time, you can have students construct their own calibration curve relating
density to concentration of salt. The concept of creating calibration curves is a key concept of
experimental science. All measurements, in one way or another, are made by comparing against
a known standard or measured calibration curve. In this case, students can make a series of
mixtures of salt and water of known composition (and constant temperature), measure the
volume and mass of each, calculate density and plot density as a function of salt concentration in
order to derive the calibration curve.
Your answer to the question: what was the temperature of that melting event?
#3 Physical Geology: How we "see" into the Earth with seismic waves
Russ Colson-MSUM
Sometimes experiments are qualitative rather than quantitative, and may involve observations
rather than measurements. Even so, one must be rigorous and careful in observations, and find
some way to record and document observations, even if they are qualitative.
When a wave (ocean wave, light wave, or seismic wave) passes into a region or material where
its speed changes, part of the energy reflects and part refracts (bends). The bending and
reflecting of seismic waves can be used to infer the nature and configuration of Earth's interior.
This activity gives students the opportunity to notice refraction and reflection and to think how
(in a conceptual way) these can be used to infer Earth's interior.
Example question to solve: The "question" for this experiment is in the form of a game-like
challenge. You will need to predict the configuration of unseen objects (analogous to earth
scientists inferring the nature of Earth's interior).
The Unknown: You will need to predict the location of 1 or two tin cans sitting in a pool of
water, hidden under a 12" wide box.
Tray with ½
inch water
Possible Configurations include the following:
Materials: Rulers or other straight edges to generate waves, a large basin of water, 2 tin cans, a
bucket to carry water.
You have 20 minutes to design experiments and record results with a similar set up in an effort to
understand how wave reflection and refraction might give you enough information to predict the
configuration that you can't observe directly. Design experiments in such a way that you will be
able to tell the configuration of the tin cans even though you can't see them (think: refraction
and reflection).
At the end of 20 minutes, you will have 3 minutes to predict which configuration is hidden under
the box (the Unknown).
Your configuration is:
#4 Weather: What causes water to condense from the air, making clouds, rain, and snow?
Meteorology, although one of the earth science disciplines, is really a great way to learn applied
physical science. Experiments in physics and chemistry can yield insight into what causes
weather events.
Example question: How does the humidity of air change if I keep the amount of moisture in the
air the same, but decrease the temperature by 10ºC?
Materials: 2 liter bottle, plastic modeling clay or other pliable sealant, digital T-humidity device
with remote sensor, basins, hot water, cold water, ice.
Experiments: Put some air in a bottle and seal up the bottle. Run the wire lead from a digital
temperature and humidity gauge into the bottle (in such a way as to maintain the seal). Record T
and humidity. Place the bottle in a bath of hot water, and record T and humidity as they change
together. Place the bottle in a bath of ice water and record how T and humidity change together.
Plot on a graph of temperature versus humidity.
Take note that condensation begins to form on the inside of the bottle sometime after 100%
humidity is reached.
What is your answer to the question: How does the humidity of air change if I keep the amount
of moisture the same, but decrease the temperature by 10ºC
Related learning activities:
Blow up a balloon, hold it against your face, let the air out quickly while holding it against your
face. How does the T change?
This is an example of "adiabatic cooling" in which T falls due to a change in pressure. This is
what causes clouds to form and rain or snow to fall: air rises (because of a low pressure area or a
front), causing pressure to fall which causes the air to expand which causes the temperature to
fall (adiabatically). Cooler air holds less water and so relative humidity rises (relative humidity
= the amount of water vapor in the air divided by the maximum water vapor the air can hold at
that temperature). When it rises to 100%, condensation occurs.
See attached humidity learning activity.
Some notes on experiments, simulations, and illustrative activities
An experimental simulation tries to reproduce all the natural conditions under which some
process occurs in nature with the intention of understanding the process better. Students in earth
science, when asked to do an experiment, usually do a simulation instead. (computer simulations
are similar, except the natural conditions and results are modeled from basic physics principles
through use of a computer programming)
An experiment is more controlled than a simulation, looking at fewer variables and trying to
avoid having everything "just like in nature" (because then we don't really understand what event
caused which effect). Experiments try to examine the effect of changing one single variable at a
time.
An illustrative activity is not an experiment or simulation, but rather is an activity that helps a
student understand a concept. It is constructivist learning, but would not be something a scientist
could use to prove a point to another scientist (although it might help other scientists understand
the concept).
Ice Cream in a Bag--A Journey in Phase Equilibria!
Russ Colson-MSUM
Fill a gallon ziplock bag half full of ice. Add 6 Tablespoons of salt. Set aside.
In a 1 pint ziplock bag, mix ½ cup milk, ¼ cup half and half cream, 2 tablespoons
sugar, and ¼ teaspoon vanilla. Squeeze out the air and seal securely (very
important it be sealed!).
Place the double-bagged ice-cream mix in the gallon bag with the ice. Zip closed
and shake and massage the ice-cream until the mixture reaches ice-cream thickness
(perhaps 5-8 minutes). Open large bag and discard ice and salt-water. Rinse salt
water from the inner bag and dry. Snip the corner of the bag and eat ice-cream
with a spoon.
Ponder how phase equilibria is responsible for most of the joys of life.
Salt-Water phase diagram
Earth Science Today
Russ Colson
Minnesota State University Moorhead
Illustrative activity: What are condensation/humidity/dewpoint?
The following activity is an illustrative activity, not an experiment. An illustrative activity helps
one understand a concept that has already been figured out through experiments by other people.
This activity was developed for Project Atmosphere and published by the American
Meteorological Society (1993), who grant permission for its reproduction so long as it is used for
non-commercial educational purposes.
Activity: Water Vapor Investigation
Materials
Four 12-ounce clear or translucent drinking cups for every group, enough Styrofoam "peanut"
packing material or popped popcorn (we will use beans) to fill one cup.
Objectives
After completing this investigation, you should be able to:
• Explain with cups of different sizes how the "capacity" of air to hold water vapor varies with
temperature.
• Use the cups and beans as a model to explain relationships between the "capacity" of air to hold
water vapor and the actual amount of water vapor in the air.
Method
Cups of different sizes are used in this exercise to represent the "capacity" of air to hold water
vapor at 0, 10, and 20 degrees C. Beans are poured into the cups to represent the water vapor
actually in the air.
Start the activity by filling the large unmarked cup approximately level with beans. Tap the cup
gently on your table or desk top to help the material settle as you fill the cup. This is the supply
of beans you will use in this exercise.
This activity involves the use of four cups. The unmarked cup is used to store the beans. The
largest marked cup is twice the capacity of the mid-size cup. The mid-size cup is twice as big as
the small cup. The marked cups represent the "capacity" of air to hold water vapor at 0, 10, and
20 degrees Celsius. Each cup is labeled by the temperature related to its capacity.
1. Fill the small 0-degree cup with beans until the contents are level with the top of the container.
Pour the contents into the mid-size 10-degree cup. Repeat this until the 10-degree cup is level
full. Now pour filled 10-degree cups into the 20-degree cup until it is full. Assuming the cups
represent the capacities of air to hold water vapor at 0, 10, and 20 degrees, complete the
following statement:
The capacity of the air to hold water vapor approximately ______________ when the
temperature increases 10 Celsius degrees.
2. Starting with a filled 20-degree cup, pour its contents into the 10-degree cup until it is level
full. Now pour the contents of the 10-degree cup into the 0 -degree cup until filled to the brim.
Now complete the following statement:
The capacity of the air to hold water vapor approximately ________________when the
temperature lowers 10 Celsius degrees.
3. Now empty the 20-degree cup and pour filled 0-degree cups into the large cup until it is full.
Based on this, complete the following statement:
The capacity of the air to hold water vapor increases approximately by a factor of
____________ when the temperature rises 20 Celsius degrees.
4. According to the same observations, what happens to the capacity of air to hold water vapor as
the temperature falls 20 Celsius degrees?
5. When air cools, its capacity to hold water vapor decreases, and any excess water vapor must
condense. This can be demonstrated by attempting to pour all the beans from a filled 20-degree
cup into the 10-degree cup. Level the top on the 10-degree cup. The overflow represents the
water vapor that condensed out. In this example of the 10-degree cooling, how much of the water
vapor condensed to liquid as the temperature dropped 10 degrees?
6. Air filled to its capacity with water vapor is called saturated air. If saturated air at 20 degrees
is cooled 20 degrees, how much of its water vapor must condense?
7. Saturated air has a relative humidity of 100%. Relative humidity is a measure of the amount of
water vapor actually in the air compared to the amount it would hold if saturated at the same
temperature. Pour a full 0-degree cup into a 10-degree cup to determine what the relative
humidity would be if air saturated at 0 degrees is warmed 10 degrees with no addition of water
vapor. What is it? What would the relative humidity be if that same air were warmed another 10
degrees to 20 degrees Celsius?
8. Explain in your own words why in cold weather the relative humidities in heated buildings
(without humidifiers) are quite low.
9. Dew point is another common humidity measure. It is the temperature to which air has to be
cooled (without changing the amount of water vapor in the air) to become saturated. Whenever
air is saturated, its temperature and dew point will be the same. What is the approximate dew
point of air at 20 degrees with a relative humidity of 50%? To find out, fill the 20-degree cup
half full. Then, pour it into the 10-degree cup.
10. What is the dew point of air saturated at 0 degrees when the air temperature is raised to 10
degrees without the addition of water vapor? To find out, pour a filled 0-degree cup into 10degree cup and ask yourself whether or not the dew point changed.
11. If saturated air at 20 degrees is cooled to 10 degrees, what is its final dew point? To help find
your answer, attempt to pour a filled 20-degree cup into 10-degree cup while asking yourself
how much water vapor the 10-degree cup is holding compared to its capacity.
12. In general, when saturated air is cooled, what happens to its capacity to hold water vapor, its
dew point, and its relative humidity? Refer to your observations made above.
13. Describe, in your own words, the water vapor and temperature relationships which must exist
for cloud, dew, and frost formation.