Placing Deep Time In Tangible Space

I agree with Barrow (ABT February 2016) that students benefit from a physical analogy for deep time, and I think that a 4.5 m strip of paper would be useful to stretch across a classroom. For feeling the magnitude of deep time, however, I suggest that bigger spaces allow something more. Colleagues LoDuca and Ojala in the Geology & Geography Department at my institution suggested placing events on a football field and shared that strategy in the Journal of Geoscience Education (1998).

Since accessing a playing field is not always feasible, I have had students pace along a long sidewalk outside of our building. When weather and time are limitations, I have also tried this in the classroom or hallway. Students who represented the origin of life and the first rise in atmosphere were alone far back, while students representing changes in vertebrate groups were clustered together, without room even to swing their backpacks. Results suggest that student preconceptions are altered more by the action of physical movement on the time line.

I am concerned about one detail in the Barrow article. In Table 1, the date for the “first evidence of life” is said to be 1.6 billion years ago. This is at odds with the date of 2.5 billion years found elsewhere in the article. Perhaps 1.6 billion years was provided as an estimate for the appearance of first known eukaryotes. Argument continues about first evidence of life in the fossil record, but this controversy is about rocks over 3 billion years old. I often give students a range from 3.2 to 3.8 billion years ago. Although this range is as much time as the entire animal fossil record, we still get about half of the history of life occurring before eukaryotes show up, and the vast majority of the history of life before any large remains of animals. These general proportions are important to foster in student thinking about the history of life on Earth.