Earth system science represents an important new way of looking at our planet, but it is difficult to help students learn, in an experiential mode, about the complex dynamics of earth systems. Here, I describe how the computer program STELLA can be used to construct and then experiment with a variety models to illustrate some important concepts of systems dynamics. A very simple model of a bath tub with a faucet and a drain serves to illustrate a wide range of systems concepts including residence time, response time, lag times, and feedback mechanisms. Variations on the bath tub model provide examples that illustrate the problem of model complexity versus simplicity. A more complicated model of the global carbon cycle is used to demonstrate one means of model validation, testing the model against the historical record of CO₂ buildup in the atmosphere, using as input the historical record of fossil fuel emissions and land use changes.