ABSTRACTThe ability to accurately reason using three-dimensional visualizations is vital to success in STEM disciplines, particularly the geosciences. One impediment to learning from visualizations is spatially-based misconceptions. Such errors can arise from a range of sources (e.g., prior beliefs, inaccurate application of analogy, and visual illusions). Of these sources, the potential for perceptual illusions to cause difficulty when reasoning with visualizations has been relatively unexplored. The experiments reported here consider misconceptions evident in a common type of geoscience diagram, 3D block diagrams of depositional environments (facies diagrams). Our results demonstrate a pattern of errors in temporal reasoning that we interpret to have a perceptual origin. Two experiments explored novice conceptions about the relative age of different locations in the rocks depicted in a facies diagram. Novices had difficulty reasoning about the temporal evolution of these regions. Errors appeared to be systematic, not the product of random guessing. The most common error was incorrectly treating all visually similar and connected areas as a single unit that had a common temporal origin. This error can be interpreted as the product of visual unit formation. Each experiment also explored the effectiveness of a diagrammatic intervention intended to highlight the relationship between space and time. Despite salient spatial indicators of the relationship between time and space, visual continuity and discontinuity strongly controlled temporal estimates of novice viewers.