Ben Tomlisson, BHP Teacher
Washington, USA

By Unit 5: Life, students are familiar with the concept of thresholds of increasing complexity. They’re also aware of how these thresholds represent key turning points in our Big History story. It’s important to have students question and evaluate the Goldilocks Conditions and ingredients for these thresholds because doing so reinforces Big History concepts and student understanding of the narrative, and invites them to think like historians.

Eight thresholds of increasing complexity

An opportunity for taking a close look at thresholds arrives in Lesson 5.1 with the activity Are These the Right Mini-Thresholds of Life? David Christian establishes six “mini-thresholds” that bookmark the development of life on Earth, which is Threshold 5. Are These the Right Mini-Thresholds of Life? invites students to evaluate whether those six mini-thresholds are correct, and whether a different or additional threshold should be included in the list. (Christian’s mini-thresholds are photosynthesis, eukaryotes, multi-celled organisms, brains, land, and mammals.)

Six mini-thresholds of life

I love this activity, and add a few of my own twists. Here’s how I approach it:

First, I have students quickly engage in a simple chronology card sort that I designed (you’ll find the template here). Students are given a description of each of Christian’s six mini-thresholds, and must give each mini-threshold a title and use logic to determine the mini-thresholds’ chronological unfolding. Then, we watch the animated David Christian video, in which he journeys through the mini-thresholds of life. Students check their own chronology-sort against David Christian’s, make any adjustments needed, and glue the result into their notebooks.

With this knowledge base, we move into the activity itself. I have students work in small groups to determine which mini-threshold of life they would add to Christian’s list, and why. Then, they create a poster for this mini-threshold with supporting visuals (I posted some past examples in the BHP Teacher Community.) Ultimately, I have students present their work to the class and engage in a discussion about whether we’re missing any mini-thresholds, and whether any are more important than others.

The biggest challenge students have is identifying the Goldilocks Conditions for their proposed mini-threshold. This challenge can be overcome by guiding students to ask the right questions. For example, you might ask students about the last mini-threshold: Why would species be more successful as mammals? How did this new complexity help? By answering questions like this, students can work backwards to speculate what might have caused this change.

Thresholds equation

I like the way this activity gives students an opportunity to create a part of the Big History narrative, and that they must think like historians and scientists. This activity also emphasizes BHP concepts of thresholds and scale (we can divide large events into smaller, interconnected events), which will serve students throughout the course. In fact, you might encourage students to break down each of BHP’s eight thresholds into smaller mini-thresholds, just as they’ve done for Threshold 5.

About the author: Ben Tomlisson teaches Big History as a full-year ninth-grade elective at Mount Si High School, WA, where he has taught since 2005. Mr. Tomlisson hails from Manchester, England, and has taught in Japan. He loves that Big History provides the space where he and students can build relationships and ask meaningful questions.

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