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. For geoscience students, learning these skills and content is no easy undertaking, and it requires repeated practice. But an appreciation for geologic time is important for all citizens, not just geoscientists. The perspective provided through the long history of the planet is critical to developing ways to live sustainably on Earth in the future. Helping all students develop their temporal reasoning skills and understanding of deep time is an important component of facilitating geoscience literacy.
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
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
Connections to big ideas, essential principles, and fundamental concepts about temporal reasoning in the geoscience literacies
- Earth Science Big Idea 2. Earth is 4.6 billion years old.
- Fundamental concept 2.1. Earth's rocks and other materials provide a record of its history.
- Fundamental concept 2.7. Over Earth's vast history, both gradual and catastrophic processes have produced enormous changes.
- Earth Science Big Idea 3. Earth is a complex system of interacting rock, water, air, and life.
- Fundamental concept 3.4. Earth's systems interact over a wide range of temporal and spatial scales. These scales... operate over fractions of a second to billions of years.
- Climate Literacy Essential Principle 4. Climate varies over space and time through both natural and man-made processes.
- Fundamental concept A. Climate is determined by the long-term pattern of temperature and precipitation averages and extremes at a location. Climate descriptions can refer to areas that are local, regional, or global in extent. ...
- Atmospheric Science Essential Principle 4. Earth's atmosphere changes over time and space, giving rise to weather and climate.
- Fundamental concept 4.3. Both weather and climate vary by region based on latitude, altitude, land use, proximity to physical features such as the ocean and mountains, and ocean currents.