Investigation of children's understanding of the earth can reveal much about the origins and development of scientific knowledge. Vosniadou and Brewer (1992) claim that children construct coherent, theory-like mental models of the earth. However, more recent research has indicated that children's knowledge of the earth is fragmented and incoherent. By testing the influence of question type (open vs. forced-choice questions) and medium (drawings vs. 3-D models) on the responses of 6-year-olds (N=59), this study investigated whether, and how, methodological differences account for the discrepant findings of previous research. Both the use of drawings and of open questions (Vosniadou and Brewer's methods) were found to increase the apparent incidence of naive mental models. Moreover, the combination of 3-D models and forced-choice questions elicited more scientifically correct responses and higher proportions of scientific and inconsistent mental models than the combination of drawings and open questions. It is argued that children know more about the earth than the mental model theorists claim, and that naive mental models of the earth are largely artifactual.