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Sample Discussion Thread
This discussion was selected from the AMNH online course Earth: Inside and Out. This is an excerpt from an actual course discussion, but learner names have been changed. Earth: Inside and Out is part of Seminars on Science, a program of online graduate-level professional development courses for K-12 educators.

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Week 5 Discussion: Modeling as an Earth science tool
What do you think are the strengths and limitations of modeling as a tool in Earth science?

Michael (initial post) 30 Oct 9:44 AM
Models help concepts break the "abstract" barrier to penetrate the "concrete" world! Modeling is a very positive and powerful means to explain geologic (and many other) processes that we don't have access to observe directly.

One of the best examples of these processes that happen "behind close doors" is the Mantle activity. Too bad not to be able to see with our eyes that the Mantle churns (convect) continuously! Thanks to the use of Model as a tool to "recreate" processes that we know that are happening, but that we just can't see with our eyes, we can "experience" what's going on right beneath our feet. Thanks to the use of models the Mantle Convection (the rising of hotter, buoyant rock and the sinking of cooler, denser rock, and the main mechanism by which Earth loses heat, it drives the Earth's plates, build mountains, cause faults to rupture and volcanoes to erupt, impacts the chemical composition of the ocean, and also impacts the circulation in the atmosphere and oceans impacting climate) is an understandable activity to us, no matter that we can's see it directly, or that the process happens over millions of years which is a time that is no accessible to us by direct observation. The answer is computer models to study the process! Models allow scientists to make observations and "educated" predictions.

I pretty much agree with the opinions expressed by some of you when saying that although computer models help a lot to understand processes....nothing beats observation! Models are an excellent tool to study scientific processes, but they should always be accompanied by observation (when possible). One example of models that can carry flaws is the study of cells divisions. Cells division models help us understand this very important process that occurs inside us. But there are many details and intricacies involved in this process (that models can't show).......direct observation (using lab tools) is far better to understand it.

Summing up, models are excellent and very positive tools for learning, but they have limitations and people can be misled by relying totally on them. The solution? Use direct observation (when possible) to complement the knowledge acquired through modeling. Always remember that direct observation is the frosting on the cake!

Ellie (response to Michael) 30 Oct 1:00 PM
Michael, I agree with you as well as with what others have said. I think computers are not always accurate, and that people are too reliant on modern technology. However, with that being said, I think that there are many advantages to modeling and that it is the next best thing to observation. Modeling allows researchers to observe mantle convection which cannot be observed by the human eye. We have a better understanding of viscosity, the property in which materials flows (or are resistant to flow), and how this impacts the surface of the earth. As the article, Mantle Convection, explains, "Dr. Bunge's model has thus led scientists to new understanding of the physical properties of rocks deep within the earth." The model has helped researches understand that viscosity increases with depth, a concept that was unknown before modeling. Therefore, while there are some limitations to this form of technology (and people should be aware of these limitations) , I think that there are many strengths and advantages to computer modeling as well. Ellie

Instructor: Irene (response to Ellie) 30 Oct 2:08 PM
Hi Ellie, You brought up some good points. How did scientists discover that viscosity increases with depth? Was it just with computer modeling?
Cheers, Irene

Mia (response to Irene) 30 Oct 8:45 PM
If I understood the reading correctly, scientists discovered that viscosity increases with depth from actual experiments such as the one done upon the marble columns and the observation that mineral structures become more tightly packed as pressure increases and viscosity increases. That viscosity increases with depth was not understood by modeling, but rather the other way around - the new understanding helped reshape the model.

Also, a question-no one has mentioned that more tightly packed mineral structures are denser - and the convection of all kinds is dependent for the most part on density due to temperature, structure, or composition. Is this just such a simple observation that no one mentions it, or am I off?

Scientist: Sophia (response to Mia) 31 Oct 2:11 PM
Hi Mia,
You point out the obvious that in convection the light stuff rises and the heavy stuff sinks, but it's not always obvious what causes density differences in materials. For example, there's such a thing as compositional convection, in which density difference is caused by compositional difference rather than temperature difference. A good example is in the ocean, where subtle differences in salinity can drive convection. Minerals of the deep mantle are indeed characterized by compact structures and are thus much denser than minerals of the shallow mantle. What drives mantle convection, however, is heat, and the differences in temperature are large enough to overcome the otherwise stable density structure. Sophia

Sophie (response to Michael) 2 Nov 05 10:41 AM
I agree to the advantages of modeling. One big advantage is in the classroom. Technology can bring earth science to life.

Instructor: Irene (response to Michael) 30 Oct 2:18 PM
Good job Michael. I like your first sentence. Have you used modeling with your students? Cheers, Irene

Michael (response to Irene) 2 Nov 05 6:33 PM
Hi Irene, I have been very active modeling in my Bilingual 5th grade Earth Science class lately. A few days ago I was using a basketball (to represent the sun) and I placed around the "sun" different fruits (strawberry, lemon, lime, plum) to represent the different planets and their orbits around the sun.

Also the other day when I was teaching about "day and night" I did the same set up, but this time using a super sized basketball (as the sun), a volleyball (as the earth), and a flashlight attached to the "sun" and pointing at planet earth to simulate the sunrays aiming at one side of the earth (day) and of course the opposite side of the earth didn't receive any sunlight (night). Modeling gives me a great advantage helping my students understand key scientific concepts since modeling help them visualize them. In the next days I will use computer models to teach the formation and eruption of volcanoes.

Rajen (response to Michael) 2 Nov 05 7:23 PM
Michael-I have found that using a model to demonstrate of the phases of the moon to be very helpful. I stand in the middle-with a light bulb (the sun) I have the students stand around me each with a smooth styrofoam ball on top of a stick, representing the moon, the way the light from the light bulb reflects off and shades the balls demonstrates the phases. Rajen

Michael (response to Rajen) 4 Nov 05 4:34 PM
Very Clever Rajen! I like your idea to demonstrate of the phases of the moon. Kids love when they are active part of the demonstrations/lessons! I will incorporate your idea in one of my lesson pretty soon. I love modeling because as I said before, "Models help concepts break the "abstract" barrier to penetrate the "concrete" world! Thank you for sharing your very practical/model with me.

Rajen (response to Michael) 4 Nov 05 8:13 PM
You're welcome but I can't take credit for that Michael-I went to a "Hands on Astronomy" workshop years ago and saw it there. It was great-it was when I was teaching in middle school, and helped the students to visualize and remember the phases. I remember having a substitute teacher when I was in school (many, many moons ago) and she was trying to explain what electrons were -no one was paying any attention to her until she jumped on top of the desk, put her arms above her head and clasped her hands together and moved them around and said "my head is the nucleus, and my arms are the electrons." Not exactly the most accurate "model" but it did get everyone's attention! Rajen

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