Research about geologic time conceptions generally focuses on the placement of events on the geologic timescale, with few studies dealing with the duration of geologic processes or events. Those studies indicate that students often have very poor conceptions about temporal durations of geologic processes, but the reasons for that are relatively unexplored. Close connections between ideas about time and space over short time periods, as well as poor number sense for numbers in unfamiliar ranges have been repeatedly demonstrated. This study explored whether the conceptions geoscience novices hold about the temporal duration of geoscience processes across a variety of temporal scales are influenced by their ideas about space and large numbers. Seventeen undergraduates in an introductory geoscience course participated in task-based qualitative interviews. Students tended to equate spatial size with temporal duration over short and long time periods, sometimes modifying contradictory data to fit their interpretation. Confusion about the relative size of temporal periods up to 100,000,000 years was observed. They described durations operating on long temporal scales in largely qualitative, imprecise terms. Spatial compression of large temporal periods and expansion of short time periods were common. Students possessed few specific temporal markers for durations of task events. Specific pedagogical and curricular recommendations are discussed.