Investigating the Biosphere with Planetary Models

Gregory Hansen
1991 Woodrow Wilson Biology Institute


After active participation in this activity, students will be able to:
  1. recognize the use of computers in modeling living systems;
  2. model the assumptions of the Gaia hypothesis in Daisyworld;
  3. analyze the components of the biosphere in relation to there effect on global change;
  4. discriminate between cause-effect and correlational relationships;
  5. evaluate current practices in terms of their effect on the environment.


The Gaia hypothesis, presented by James Lovelock, has been a focus of debate in the scientific community since its introduction. While the validity of such a model is still questioned, the framework of Gaia presents interesting possibilities for hypothesizing and experimenting with a structure of life as large as the biosphere. Viewing the homeostatic mechanisms proposed requires measurements with a framework in the geological or evolutionary time scale, in other words, impossible in the high school laboratory. Computer modeling, therefore, of such a system has proven invaluable to Lovelock in his defense of his ideas and allows ready access to the variables which may affect the system.

Planetary models, available in commercial software packages like SimEarth, are useful tools in modeling many aspects of the Gaia hypothesis. With this program, users may control many biological, geological, and cultural variables which effect real or created worlds in subtle and/or dramatic ways. The manual included with the software provides extensive background information, as well as, clear and concise instructions for using the program. The best preparation for presentation in the classroom is to play, experiment, and construct with the program itself. This activity will present some general methods for presenting planetary models in the classroom and possibilities for student interaction with the program, as the power of this tool is best appreciated by students through structured play with the models they create.


  • SimEarth is available on both IBM and Macintosh venues in local computer stores and via mail-order.


The presentation of any computer program requires different approaches depending upon the availability of computers in the classroom. Teachers who only have access to a single computer may find that students working in small groups to develop hypotheses, plan experiments, reach conclusions, and evaluate procedures benefit from both the group collaboration, as well as, the use of the program. If a computer and program is available to every student, a greater number of experiences will be generated at a time. An optimal situation might be when computers are available to every collaborative group and a balance is reached between the benefits of group process and range of experiences.

Introduction of the program in any of these three scenarios, in my experience, is best accomplished by the well-versed teacher running through some of the available options; different tools in the edit window, information boxes in the map window, various graph windows, and model control panels; for the entire classroom. Students may then be instructed in creating their first planet using a limited number of �-energy points (easy game) and the random planet option. Before presenting students with a problem to solve, they may require time to experiment with the various tools available on their own and just to 'get the feel of' the program.

Once familiar with the program, students will be able to model the biosphere and manipulate variables affecting change. Students should plan their experiments with the help of others, regardless of the availability of computers in your classroom. Access to the computer simulation can be controlled through the use of the question presented at the beginning of each new session, and only allowed when the student or student team has described their question, hypothesis, and methods of investigation. If one computer is being used for the entire class as in other configuration, the teacher will need to assure that student teams only perform their stated investigations and return to the task of reaching conclusions and evaluating procedures before continuing with new experiments. Appropriate questions to be answered by SimEarth are listed on the following student worksheet. The order of questions ranges from least to most difficult and students may need guidance in stating appropriate questions for their level of expertise.

Planetary Models: Student Investigation


Select a question to investigate from the following list or suggest one of your own. State your question in the space provided

  1. What might be the impact of reduced axial tilt on a planet?
  2. Given earth in the Cambrian era, what would be the effect of increased volcanic activity? meteor impacts?
  3. Given the current earth, what might be the impact of increased of sustained use of fossil fuels?
  4. Using Daisyworld, might the processes of living things serve as a homeostatic mechanism?
  5. What are the short-term and long-term effects of increasing reproduction rate in animal?
  6. What factors affect species diversity?
  7. What allocation of energy on the current earth seems to maximize human survival? planetary health?
  8. What strategies may be required to "terraform" planetary neighbors?

Clearly state the question you seek to answer through experimentation with the planetary model.


What is your tentative answer to the question stated above?


How do your plan to test your hypothesis? Prepare a detailed list of procedures you will follow and describe the variables you wish to alter. You should also offer a method for establishing a control for your experiment i.e. provide some basis for comparison.


Did your experiment lead you to accept or reject your hypothesis? Describe the aspects of your experiment which were significant in your decisions.


Answer the following -
  1. What improvements would you make in your experiment on the planetary model?
  2. What implications might your experiment have concerning today's world?
  3. Describe how you would present your findings to the rest of the class.

Woodrow Wilson Index

Activities Exchange Index

Custom Search on the AE Site