Stella Model

The process model  that allows wood to become petrified rock.

STELLA has always, philosophically, been a tool for supporting learner-directed learning. Version 7.0 delivers a set of 

features that fully support teachers in making learner-directed learning a reality in their classrooms, as well

as in "distance" settings. It also supports researchers in making their findings, or thinking-in-process, 

available to colleagues and funding sources in a more hands-on, "discovery oriented" format.

The major advances in Version 7.0 lie in the arena of communicating. We've made substantial improvements to the mapping 

language that will render STELLA diagrams more "readable." We've also increased readability by significantly enhancing the 

"storytelling" capability that first appeared in Version 6.0 of the software. It's now possible to unfurl a bit of your model and then 

to simulate just that bit to add the associated "behavioral" dimension. Drop down a little more structure…then simulate to see 

what it has added to the dynamics. By enabling "just what's showing" to simulate, people can build up their understanding of the

relationship between structure and dynamic behavior in a systematic fashion-and the pace of the building up is completely under 

the control of the "reader." Experiential learning at its best!


Using file “fossilWood.STR  The STELLA software can be adapted to any area of the curriculum or course content.

When students begin to understand the concepts of stocks, flows, connectors, and converters, you are offering them a language they 

can use to explain the world around them and the interrelationships that impact change.”

You can download the latest version from the above Stella web site or purchase the software for use in the classroom to run the

file “fossilWood.STR” or you can access their Download reader from their web-page at

for either the Windows PC or Mac.


The following keys can be used to set up any similar model to the wood petrification file demonstration as shown by the overview of the operating environment procedures identified in the top menu item of the HELP section once the application is opened.


Petrified Wood Model

What processes are required for decaying wood to become petrified?  Students can use “Brainstorming” to see what ideas they can piece together from prior knowledge. Teacher led discussion can pull the general consensus together from the group ideas to use for exploring the demo model presented here.


What step would most likely be required to begin the petrification?  Logically listing the steps would permit students to visualize the process for setting up a similar model in an organized fashion.



Using the Flow symbol we started from a Water Source where this would be our initial variable. Without this water would the process be possible?

Whether the water is from underground streams, aquifers, rivers, streams, lakes, or a similar resource like rain or snow melt we need to simulate a living system. Using the Stock symbol the water feeds into the area we have labeled the Black Swamp. This is typical of the local area where we have our trees buried in silt, sediment, volcanic materials, or combinations thereof the model is setup.

In this setting the depth of the buried trees is not determined but could represent another variable to the process. The type soils and layers would add another dimension for consideration for future variables.  The porosity of the permeable soil would be another consideration for variables, and we know this is impacted by the local temperature providing additional limits in a bigger model. We might even add pressure from the depth of debris and soil above our buried trees as a factor for a bigger model. A true model would include these steps.

Analyzing known petrified trees we know there are primarily 17 minerals that make up the chemical changes that allow the tree to become petrified.  Isolating two or three of these for our model we use another Flow and Stock symbol to represent these additional requirements.

If one or more of these minerals are present will petrification take place?  Do we need all the minerals to have petrification?

What would happen if only two minerals were present? Our model is simulating the two most common minerals found in petrified wood, calcite and silica.

What happens if we change the Flow rate of the water?  What if the Volume of the water changes?  How would increases of water affect the model?  Conversion symbols are used in our model and links arrows are used to connect these variables in each step of our model. The Variable of “flow rate,” “volume,” and “increases” in water are linked to a unit of time called the “dwell time.”  These are related and affect the model.  Students can add sliders buttons to see how changing each variable affects the overall outcome.

Interactive minerals like “Calcite” and “Silica” are only the two most common minerals, but it is important to evaluate the

Concentration, Flow-Rate, and Volume related to the “Dwell Time” interacts to make the process possible we look at adding

the necessary converter symbols and links.  By adjusting these values once a buried log has a water source to bring the minerals to the log we can begin to determine what happens next.  Does the log become Permineralized?  Are there enough minerals to complete the Petrification process?  The type minerals involved alter the changing color patterns found in Petrified wood. What colors might we expect to find if “Calcite” is the dominate mineral?  What colors might we expect if “Silca” is the dominant and most common mineral?  Please refer to Activity 2 on Physical Properties on Minerals.

Time permitting other common minerals can be added to the model. In this scenario a simple model can be made more complex and later become a Super-Model by adding these additional components. If real data is unavailable one can always simulate data in lesser proportions for the remaining minerals and set limits for each.

What minerals might be helpful to determine the age of the Mineralized and Petrified Wood? Were these minerals used in this model?  See the activity “Determining the Absolute Age of Fossils” for related extensions.



Not all teachers may know the answers to the above posed questions, however, nearly all are provided adequate information in the material provided elsewhere in the lessons or activities. The material and questions are furthered supported by University and Government Resources which can be accessed through links in the related Project materials. Access can be found on the web page for “References and Resources.” Additional links allow Teacher or Student to ask an expert in “Inquiry Based” format.



What might be the difference of water & mineral absorption of decaying wood at different depth levels?  How much Time is required to complete the petrification process?  How might different types of wood change the factors for organic materials to become fossilized and form the petrified rocks we find? I.e., the difference between the Palm trees, Deciduous Hardwoods, or Fir/Pine tree types might alter what petrification processes?



Manipulative web based model file fossilWood allows students to input and see visual changes in the variables

that have general affects on the petrification processes in a simplified format. Graphs change as the slider bars alter the data variables.  One can access the resource code “HTML” and make more changes in the data limits. Current data is from actual government and university research. Time frame is simplified.