Using Carbon Isotopes in Astrobiology: Origin of Life and beyond

Phoebe Cohen, Williams College
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Summary

Carbon isotopes are used in many different ways by scientists to reconstruct Earth's past. For example, we can use carbon isotopes to determine when life first evolved on Earth, and to learn more about what types of foods ancient animals ate. We can use carbon isotopes this way because of one simple fact - when photosynthetic organisms like algae and plants take up carbon dioxide and change it into organic matter (i.e., their bodies), they fractionate carbon, leaving behind a chemical fingerprint of their work. This activity will walk students through a model of stable carbon isotopic fractionation using bingo chips (or similar) and then ask them to apply their new understanding to data on the origin of life on Earth, then think more broadly about the role of isotopes in astrobiology.

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Context

Audience

High school earth science or chemistry class, college introductory earth science / geology / astrobiology class.

Skills and concepts that students must have mastered

Basic concept of what an atom, a molecule, and an isotope is, and the difference between a stable and unstable isotope. Basic understanding of photosynthesis and respiration. Comfort with fractions.

How the activity is situated in the course

Stand alone or part of a short sequence. Designed for a class period + an activity period, but modular so that multiple activities can be combined depending on time, curriculum, etc.

Goals

Content/concepts goals for this activity

Understand the process of isotopic fractionation, apply concepts to deciphering case studies including the origin of life.

Higher order thinking skills goals for this activity

Hypothesis formulation and testing, data analysis, reading complex plots, understanding simple models.

Other skills goals for this activity

Description and Teaching Materials

This activity will walk students through a model of stable carbon isotopic fractionation using bingo chips (or similar) and then ask them to apply their new understanding to data on the origin of life on Earth, then think more broadly about the role of isotopes in astrobiology.

It includes a student handout and a set of teaching slides. Ideally, the teaching slides would be used in a class period before the activity, or as a pre-lab pre-recorded lecture by the instructor.

Bingo chips are used in the handout, but many other objects can be used as well such as candies, coins, and beads.

In a large class, this can be done using a document camera with a few student helpers at the front of the room.

This activity was created with support from the National Science Foundation EAR 1855014


Student Handout for Using Carbon Isotopes in Astrobiology: Origin of Life and beyond (Acrobat (PDF) 1.1MB May19 22)
Teaching slides on stable carbon isotopes (PowerPoint 2007 (.pptx) 11.6MB May19 22)


Teaching Notes and Tips

Assessment

Assessment of student understanding can be gained via the final questions asking students to apply their knowledge.

References and Resources

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