The relevant literature has shown that student teachers hold alternative conceptions of soil erosion. Even though Turkish science student teachers are expected to teach the concept of 'soil erosion' in lower secondary schools (grades 5-8), none of the earlier studies have explored their conceptual growth and/or mental models throughout a 4-year undergraduate program. Indeed, science (student) teachers, who play a pivotal role in teaching the sustainability of soil as an environmental heritage, are able to transfer their environmental knowledge and mental models to younger generations. Therefore, the aim of this research was to elicit science student teachers' (SSTs) understanding of soil erosion. In a cross-age comparison, the sample of the research was comprised of the first-year (n=54), second-year (n=62), third-year (n=60), and fourth-year of a four-year science education program (n=65), a total of 241 SSTs, enrolled at the Department of Science Education in Karadeniz Technical University in Turkey. A questionnaire with 4 open-ended questions and semi-structured interviews were used to collect data. The results indicated that the majority of the SSTs confused the concept of 'soil erosion' with the one 'landslide'. For this reason, the current research suggests the development of analogies and computer simulations to overcome this confusion.