Teaching about Time

Gwen Daley, Department of Chemistry, Physics and Geology, Winthrop University

I am a paleontologist who works with deep time both in my research and in my teaching. I have taught courses in historical geology (lecture and lab), paleontology and the history of life (as well as other courses). My students attended both urban and rural large state universities, a small Catholic college and now Winthrop University, a mid-sized state college with a strong tradition of training future K-12 educators. I have spent most of my professional career in academia, but have also spent short stints as an interpretive ranger at Florissant Fossil Beds National Park and a chronostratigrapher for Amoco.

For my research, I have studied paleoecology and evolution as it is preserved in deep time, as well as investigating how rock-forming and fossil-forming processes affects our understanding of the history of life. I have looked at many different scales of time from taphonomic loss of information over the first few post-mortem weeks of modern brachiopod remains to persistent ecophenotypic variation in a lineage of clams through third-order stratigraphic sequences in Ordovician strata.

I have tried to impress on my students the most important lesson about deep time that I learned from Richard Bambach, that "Time is Long", but have been frustrated in my attempts to convey the scale of deep time to my students. It took me years to develop a true sense of what is meant by geologic time, which makes it difficult for me to encapsulate the concept in a package that fits into an undergraduate geology course. One challenge I have seen in teaching and learning about time is that the scales we examine are frequently discordant (e.g., a hundred foot stack of tidal rhythmites was deposited in a fraction of the time of a hundred foot stack of third-order Milankovich cycle deposits) and of vastly different lengths (e.g., how do we relate the hours it takes a boring snail to kill its bivalve prey with the millions of years that the two taxa have been co-evolving?).

I have used metaphorical approaches with mixed results. For instance, my students participated in an in-class activity in which they created a geologic time scale with a scale of 1 inch = 10 million years. The entire length of the time scale was 37 feet, which fit neatly into the hallway outside our classroom. Each group of students determined where two specific events in geologic history (e.g., the Cretaceous/Tertiary Extinction or the formation of Earth's Moon) would be on this time scale. The students then wandered up and down the time scale to get a feel for both the vastness of deep time and the relative position of various events.

The time scale exercise helped the students understand the relative spacing of events well, but did not really impress the idea of the deep time. The problem, which is common to all such demonstrations, is the scale of 1 inch = 10 million years; ten million years is an incomprehensibly large number. Changing the scale (e.g., 1 inch = 1 year) simply shifts the problem, as 4.5 billion inches is equally incomprehensible, even when converted to 71,022 miles, or 2.8 times the circumference of the Earth (the corollary to "Time is Long" is "Space is Large"). Finding a way for students to comprehend these seemingly incomprehensible numbers could pave the way to a fuller understanding of deep time.