The concept of deep time is one of the distinguishing characteristics of the geosciences. We expect geoscientists to have an intuitive sense for the scale of geologic time, the rates of geologic processes, and the uncertainties associated with ages and rates, while also having a general understanding of Earth's history.
This concept map, from (Manduca and Kastens, 2012) , illustrates the domain of time in the geosciences. Of primary interest here are the nodes of temporal reasoning, which discusses the habits of mind utilized by geoscientists about time, and pedagogy, which describes strategies for and impediments to teaching. You can download text to accompany the concept map (Acrobat (PDF) 106kB Feb19 13).
Common challenges and misconceptions
- The scale of events in geologic time does not correspond with events on the human time scale
- Students are challenged by exponential numbers and orders of magnitude, two of the basic mathematical concepts that underlie the concept of deep time
- Timelines students encounter in other classes may be represented horizontally, while geoscientists tend to represent the timescale vertically, with the youngest at the top.
- Students' cultural or religious views may conflict with the scientific understanding of geologic time
Activities that address temporal reasoning
Unit 7: Heat Flow in Permafrost
Kirsten Menking, Vassar College
Unit 9: Carbon Cycle and Ocean Chemistry
David Bice, Pennsylvania State University-Main Campus
Unit 2: The Lead Problem Still Exists: Challenges and Gaps in Understanding Exposure
Katrina Korfmacher (University of Rochester), Richard Gragg (Florida A&M), Martha Richmond (Suffolk University), and Caryl Waggett (Allegheny College)
Unit 5: Abating Carbon Emissions
Robyn Smyth, Bard College; Gautam Sethi, Bard College; Curt Gervich, SUNY College at Plattsburgh
Learning outcomes and assessment for temporal reasoning
Knowing the challenges that students face in developing an understanding of geologic time, you can develop specific learning outcomes tied to assessments that will help you move them towards experts in temporal reasoning. Learning outcomes for temporal reasoning differ somewhat from learning goals about the content of geologic time. For example, you may want students to be able to name the major eons of the geologic time scale and their characteristics, but that is not temporal reasoning or a habit of mind. Learning outcomes that addresses this habit of mind might be something like:
- Students will be able to apply rates of change from modern, observable processes to estimate the timing of events in the geologic past.
- Assessment: Students will measure or collect data on sedimentation rates in a modern setting and apply it to the rock record.
- Students will be able to analyze several lines of geologic evidence in order to interpret a sequence of temporal and/or spatial events or a geologic process.
- Assessment: Students will compare data from the Mid-Indian Ridge, Mid-Atlantic Ridge, and East Pacific Rise. (Potential data sets include bathymetric, paleomag, geochron, and heat flow.) This may involve identifying spatial and/or temporal geologic patterns and inconsistencies among data sets with the overarching goal of recognizing that differences in spreading rates produce differences on the ocean floor.
Resources for teaching about time and temporal reasoning
- Teaching about Rates and Time from On the Cutting Edge
- Teaching about Deep Time in the perspective of quantitative skills