Divide students up into groups or allow them to work individually. Bring a few different media, such as baker's clay, gray clay and Plah Doh, into the classroom for the students to work with. Have them research the dimensions of different layers of the Earth, such as the inner core, outer core, crust and mantle. Using the medium of their choice, the students' task is to create a scale model of the Earth.
Assign this project as a homework assignment. Ask the students to go home, find foods around their house or purchase some at the store and construct a model of the Earth with edible items. Give them a list of foods that they cannot us,e due to classroom allergies. Have the students present their food models in front of the class, and explain why they selected the pieces of food that they did.
Not all models of the Earth are exactly the same. Bring in some homemade models, whether they are out of clay or made from food items. Other models to include are comprehensive models, models that show rivers and mountains, models that indicate the main type of goods that a country produces and more. Have the students create a chart in which they note the similarities and differences that exist among these various types of models.
Ask the students to use models of the Earth as one of --- or the only --- sources for their research project. Provide them with a scale model of the Earth and see if they can figure out how large the Earth really is based on that scale. They could use other types of models to see how much of the Earth is water, mountains and so on. Require them to present their findings to the rest of the class, as well as in research paper format.