Academic journal article Science Scope

Revealing Alternative Conceptions to Enhance Students' Understanding of Deep Time

Academic journal article Science Scope

Revealing Alternative Conceptions to Enhance Students' Understanding of Deep Time

Article excerpt

Deep time, or the idea that Earth is billions of years old, is a difficult concept to grasp, but it is very important in science. A few summers ago, as part of a teacher professional-development program called Fossil Finders, I had the opportunity to consider my own understanding of deep time as I participated in an activity similar to the one described by Hester (2008), previously published in Science Scope ('Taking Steps to Understand Geologic Time"). During the activity, participants took a 45-step journey that represented 4.5 billion years of Earth's history. We began the activity 45 steps into the past, at the formation of the Earth. We then slowly walked forward toward the present day (step 0), with each step representing 100 million years. With each step we took, our leader pointed out when various events in Earth's history occurred (e.g., Pangaea forms, first land plants, dinosaurs become extinct, Neolithic period of human history). While participating in the activity, I was amazed at how far off my predictions were regarding both the order and timing of events in Earth's history. For example, nearing present day (step 0), I was surprised to find that many of the events I thought took place a long time ago (e.g., the formation of Pangaea, the extinction of the dinosaurs) were bunched up in the last few steps of the walk through time, meaning that in the context of geologic time, these seemingly ancient events were actually quite recent. Through my participation in the activity, my own understanding of deep time improved as I compared the new information I learned to my previous conceptions about Earth's history.

When I returned to school in the fall, I had the opportunity to adapt the 45-step activity for my classroom. I introduced it as part of a unit on Earth's history that asked students to imagine what the Earth looked like at a point in its distant past. The unit focused on the Devonian Period, which occurred approximately 400 million years ago. The goals of the unit were to help students:


* realize that the Earth is very old,

* explore a scale of time longer than a human life span,

* address misconceptions related to deep time (such as the belief that dinosaurs and humans coexisted), and

* understand the order of major events in Earth's history and the relative times that they occurred.

The following is a day-by-day breakdown of the activity.

Day 1: Starting with students' pre-existing ideas about the order of events

Instead of beginning with the walk through time, I place my students in heterogeneous working groups with three students per group. I give each group a set of 20 "event cards." Each card has a significant event in Earth's history (e.g., "Earth forms," "First grassland ecosystem," "Pangaea forms"). The events I use to make the cards come from Hester's (2008) activity, although one can use any set of events in Earth's history that are relevant. I use a word-processing program to make the event cards (I make a table with 20 boxes and put an event in each). Once I have the template made, I copy one set of cards per group. I use different-colored paper to make it easier to keep the sets separate. I then cut each set of cards and secure them with binder clips. The number of sets will vary depending on your largest class size. It takes me about 30 minutes to make eight sets, which is typically enough for my classes. I can reuse the cards throughout the school day, and sometimes from year to year.

I instruct groups to place the event cards in what they think is the correct chronological order. I ask students to spread the event cards out on a table, read them carefully, and arrange the cards in a line, from oldest to most recent (see Figure 1). As students begin, I encourage them to check their partners' reasoning and make sure it is sound. Their reasoning is not always perfect, as the topic is new for many of them. …

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