Geologic time is a crucial component of any geoscientist's training. Essential knowledge of geologic time includes rates of geologic processes and the associated time it takes for geologic features to form, yet measuring conceptual thinking abilities in these domains is challenging. We describe development and initial application of the Landscape Identification and Formation Test (LIFT), a concept inventory for measuring abilities to identify landscapes and their formation timespans. Test development included careful choice of concept questions followed by a cycle of validation steps involving student and expert think-aloud interviews. We then administered the test, together with eight validated questions about geological time, to 96 university students in second year and fourth year geoscience courses. Results showed that students' abilities and confidence were more closely aligned with their general knowledge about geologic time than with the level of the course in which they were enrolled. Students were better at identifying landscapes than estimating how long they take to form, and both students and experts had the most difficulty with intermediate formation timespans. Details about students' errors, including common landscape misidentifications and systematic errors in estimating formation timespans, can help instructors prioritize the content and pedagogy of their courses. The LIFT is a validated concept inventory that is available for anyone to use as a pre-post, diagnostic, progress, or end-of-degree assessment that can provide valuable feedback about knowledge and learning to students, instructors and program administrators.