Some ability to comprehend deep time is a prerequisite for understanding macroevolution. This study examines students' knowledge of deep time in the context of seven major historical and evolutionary events (e.g., the age of the Earth, the emergence of life, the appearance of a pre-modern human, "Homo habilis"). The subjects were 126 students recruited from psychology, education, and biology classes at two universities. They were assigned to stronger and weaker background groups based on their college-level biology coursework. Subjects provided startlingly large time ranges for all questions, ranging over several orders of magnitude (e.g., from 1,000 to 600 billion years ago for when most dinosaurs became extinct), coupled with the strong tendency to underestimate how long ago the events occurred. Converting absolute time estimates to relative time estimates allowed subjects' knowledge of the spacing of the events to be examined and also provided a clearer picture of their patterns of over and underestimation. The results of this study suggest that many students are without an effective conceptual framework to make sense of very large time frames. Although there were no consistent differences in the accuracy of students' responses as a function of their biology background, the weaker background students showed greater variability, providing more time estimates at both the low and high extremes. We describe a pedagogical strategy that uses a relative approach presenting major evolutionary events as they unfolded in time and advocate a tool from professional practice to depict events in time and space. (Contains 10 figures, 2 tables and 1 footnote.)