THINKING ABOUT DEEP TIME: THE INTERSECTION OF TEMPORAL, SPATIAL, & NUMERIC REASONING

Deep time is a fundamental geoscience concept. It involves the capacity to sequence events in relative and absolute terms on an exceedingly large scale (temporal succession). Equally vital is the ability to determine the temporal period (duration) of geologic processes that span many orders of magnitude. Learners of all ages and practicing teachers have generally poor conceptions of the durations of events and often state that geologic processes happen more quickly than they do. Why is deep time so difficult to understand? The extent of a learner’s geoscience content knowledge plays a role. Other factors may also be at work, specifically how students reason about more familiar time periods (conventional time) and their understanding of large numbers.

Prior research has focused more on how students understand temporal succession rather than their ideas about duration. This paper explores two questions about learners’ conceptions of duration in deep time. Do students reason about conventional and deep time in similar ways? Do they understand the relative sizes of numbers in the thousands or greater? Thirty-five US students, ages 13-24 were interviewed for this exploratory study. Participants watched animations of a series of horizontal layers filling under various conditions, compared the filling durations of layers, and subsequently applied the task to a line drawing of sedimentary layers. They also created timelines using temporal periods from a minute to 100 million years.

Students applied similar reasoning strategies to tasks in deep and conventional time, in both cases mistakenly equating spatial size with duration. They generally displayed poor conceptions of temporal periods greater than 100 years and often could not determine how two quantities were multiplicatively related. Spatial compression of temporal periods was evident. The connection between spatial, temporal, and numeric thinking appears to be a fruitful area of future research about deep time conceptions. Linking deep time to what students already know about human timescales and improving their knowledge of large numbers may result in improved understanding of deep time.