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.
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)
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.
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.