Teaching about Time and other Big Numbers

Roger Steinberg, Department of Natural Sciences, Del Mar College

I use several strategies to address the challenge of teaching about time—conceptual, visual, and quantitative—but first, some background. After approximately a decade of working as a professional geologist in both mineral exploration and petroleum exploration and production, I found a new passion teaching geology at Del Mar College, a community college in South Texas.

My primary teaching responsibility of the past few years has been Historical Geology, which we call "Earth History" (Geol 1404), emphasizing that it is basically a history course, with the Earth as the subject.

At Del Mar College, we (three full-time faculty) teach about 1000 students per academic year in the Geology Program, which along with biology, chemistry, and physics constitutes the Department of Natural Sciences.

Only about 5% of our students are geology majors, however, so each class of around 30 will usually have only one or two. Our classes attract students from many different fields, like business, criminal justice, journalism, and education who are fulfilling their degree-plan science requirements. I am always keenly aware of the need to educate scientifically literate non-scientists, while at the same time ensuring that my geology majors are learning what they need to know to develop a sound foundation for their future academic and professional careers. Many of our geology majors are not officially declared majors at the start of a semester, but are recruited from the ranks of the non-majors during the time that they are in our classes.

Most of our geology majors transfer to the nearby campuses of Texas A&M—Corpus Christi or Texas A&M—Kingsville to receive their Bachelor's degrees in Geology. The majority of them go on to work in the oil field, which is presently experiencing another boom thanks to the technology of hydraulic fracturing (fracking), allowing the extraction of oil and gas from the Eagle Ford Shale, one of many shale plays currently being developed in the United States.

Time is the most important consideration of my Historical Geology classes. It is mentioned during our very first class meeting and during every subsequent class throughout the entire semester. It permeates the catalog description of the course itself: "Introduction to geologic time; relative and absolute dating methods, stratigraphic principles, origin of the Universe, Solar System, atmosphere, oceans, life; changes on the Earth's surface and development of organisms through geologic time."

Time is also the key component of four of the five stated goals on the first page of my Historical Geology class syllabus:

1. You will be expected to develop an understanding of science in general and the requirements and limitations of scientific theories, and to demonstrate an understanding of what is perhaps Geology's greatest contribution to human knowledge—the realization and full appreciation of the immensity of geologic time.
2. You will learn and demonstrate knowledge of the principles and concepts used by geologists in studying the rock record to determine the history of the Earth and the history of life on Earth as revealed by fossils.
3. You will also demonstrate an understanding of the place of the Earth within our Galaxy and the Universe as well as the Earth's history in the larger context of planetary processes within our Solar System.
4. As in any other history course, you will need to learn and be able to discuss the major events and important milestones in the history of the Earth and its life. (What happened and, just as importantly, when it happened.)

Furthermore, at Del Mar College we use WEAVEonline for assessment, planning, accreditation, budgeting, and institutional priorities. One of the six Student Learning Outcomes which the Geology Program evaluates each year via WEAVE is:

"Students will demonstrate their comprehension of the immensity of geologic time."

For this project, students create and discuss their own metaphor for geologic time.

I am always acutely aware of the challenge of communicating to students the immensity of geologic time and that the duration of the Earth's history is enormous, especially compared to a human lifespan. As all geoscientists know, comprehension of geologic time does not come easily, especially for students who are studying the earth sciences for the first time. Yet an understanding of the vastness of Earth's history is invaluable, not only as an aid in studying geologic processes and rates of geologic changes, but also for a fuller understanding of evolutionary concepts and the impact of the human species on Earth—a knowledge especially important for environmentally aware citizens.

As I mentioned in the first paragraph, I use several strategies to address this challenge—conceptual (the metaphor project mentioned above is an example), visual (one of which visually communicates the immensity of just one million), and quantitative (including the metaphor project).

Finally, I've come to realize that the comprehension of the immensity of geologic time is really a subset of the comprehension of very large numbers in general. In addition to the age of the Earth, students in my classes also consider the ages of the Solar System, the Milky Way Galaxy, and the Universe. Other astronomical discussions that utilize large numbers include distances in space and the time needed to travel to places like the Moon, to the outskirts of our Solar System, to the next closest star, to Andromeda (the nearest large galaxy), and beyond. We also consider the number of stars in an average galaxy, the number of visible galaxies, and the number of stars in the visible universe (as well as grains of sand on a beach, thanks to Carl Sagan).

Radiometric age-dating presents other opportunities to examine very large numbers. In radiometric age-dating we consider the number of atoms in a small piece of wood, how much of the wood is composed of carbon, the number of carbon atoms that are C-14, and the number of atoms of C-14 that would decay each minute.

What other discussions or activities do you teach that utilize very large numbers?