Deep time - what is your metaphor?

Jeffrey Wilson

University of Michigan

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- Scientific Accuracy
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Initial Publication Date: July 24, 2009 | Reviewed: June 24, 2014 (see revision history: 2 events)

Summary

Construct your own metaphor, appropriately scaled, for communicating deep time.

Biostratigraphy/Biogeography , Event-Specific Items | College Lower (13-14)

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Context

Audience

First-year undergraduate seminar on geological controversies. This course usually includes a mix of science and non-science majors.

Skills and concepts that students must have mastered

basic mathematics
understanding the age of the earth

How the activity is situated in the course

I haven't tried this activity yet, but it will be an in-class activity that we do after lectures on Deep Time and Age of the Earth.

Goals

Content/concepts goals for this activity

I want students to learn the age of the Earth and some major landmarks in the history of life and the history of the Earth, and to appreciate the relationships between them.

I would like students to be able to work fluidly with numbers, words, and images.

I want students to think about and appreciate scaling relationships.

Higher order thinking skills goals for this activity

I want students to be able to deconstruct a metaphor (a simple, memorable thumbnail sketch), analyze it, and create their own.

Other skills goals for this activity

I want students to think about how scientific concepts are communicated to non-experts, and to appreciate the import of doing this as accurately as possible.

Description of the activity/assignment

Appreciating the depth of time is a bit like trying to understand the national debt — it is easy to rattle off the number, but more difficult to appreciate what it means. Several popular writers have tried to convey the depth of time by incoporating one major (and important!) signpost in their scales: the first historical records of humans on the planet. Mark Twain famously referred to human history as the "skin of paint" at the summit of the Eiffel Tower, and John McPhee the "stroke of a medium-grained nail file" on the middle nail of an outstretched arm.

I would like for you to evaluate these two metaphors for accuracy. How close were Twain and McPhee to appropriately contexualizing human existence in geological time? Use the pdf's of Twain's and McPhee's prose and what you know from class lectures to accomplish the following goals.

(1) Evaluate whether McPhee's and Twain's metaphors are appropriately scaled – i.e., do their metaphors correctly depict the age of the earth relative to human history? How about if we incorporate the fossil record of humans?

(2) Create your own appropriately scaled metaphor. Add in at least three other "signposts", either biological or geological, into your metaphor and explain why you chose them.

Determining whether students have met the goals

Evaluation of the first part of this exercise is straightforward. Evaluating the second part is much more subjective, because I need to assess whether they are effectively communicating the concept to others.

More information about assessment tools and techniques.

Teaching materials and tips

Activity Description/Assignment:

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Instructors Notes:
Age of Earth — 4,500,000,000 yrs

Recorded human history — 10,000 yrs

Human share of earth history — 1:450,000

Height of the Eiffel Tower — 324 m

Thickness of skin of paint — 1 mm

skin of paint's share of eiffel tower — 324,000

Average human arm span — 150 cm

nail removed by nail file — 0.10 mm

nail file's share of human arm span — 1:15,000

**Students will come up with a variety of values for the length of human recorded history, thickness of a skin of paint, and how much nail is removed by a file. This can be instructive; you can can talk about variability and error.
Solution Set:
Twain was closer than McPhee, but depending on how student's estimate the various measures they could be closer or farther from the correct answer. The most important ratio to get correct is the human share of Earth history.