Co-evolution of Life and Minerals
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Based on the 2010 Scientific American paper by Hazen, and the more technical 2008 paper of Hazen et al, both of which explore the effect of the biosphere on the tremendous number of mineral species that occur on Earth compared to the lesser number we believe we are seeing on other planets. This tackles the idea of mineralogy/geochemistry evolving over time as do biological systems, rather than being a static system with no hysteresis or temporal aspect to it. Students work in small groups to decide which groups of minerals have been most affected by a variety of biological influences, and how. Then the class as a whole compares their conclusions group by group.
Sophomore EES, Biology, and Env. Sci. majors. I always have a sprinkling of Technical Writing Majors. The activity occurs after I have done quite a lot on the biogeochemical cycling of the major and some minor elements. I have already also covered something about microbial processes, especially those that involve chemical transformations of rocks and minerals by active and passive bioprecipitation, biodissolution, etc.
Skills and concepts that students must have mastered
Basic concepts of redox and pH effects as applied to life processes, and the effects of those on the intrinsic geochemistry of different lithologies. The notion that microbes often attach strongly to crystalline faces and create pitting, the related notion that organisms in a fluid environment can alter the course of aqueous crystallization, etc.
How the activity is situated in the course
Mid semester usually. The kids have to be comfortable with the basic concepts, and perhaps more importantly, by mid semester, they have become more willing to speak up, because we have already done a reasonable number of in-class small group activities, where we then share the results of individual groups in the broader class context.
Content/concepts goals for this activity
Overlapping chemistry between the geochemistry and the biochemistry. The influence of microbial binding on crystal formation, or lack thereof. The magnitude of tangible geological evidence of the presence of life on a planet, compared to planetary bodies without such influences.
Higher order thinking skills goals for this activity
Synthesis of ideas from broadly interdisciplinary fields, namely biology/microbiology, mineralogy, and geochemistry.
Formulation of hypotheses, I ask the students to come up with an over-arching hypothesis statement for each class of mineralogical/biological classes they consider.
Other skills goals for this activity
Working in groups, choosing a spokesperson, articulating the group's consensus.
Description and Teaching Materials
Everyone is assigned Hazen 2010, and Hazen et al 2008 (as a supplementary document) a week or 10 days in advance. Students break into small groups, 3 to 5 depending upon total class size. They have copies of the papers in hand. Each group selects one major category of minerals mentioned in the papers. They specifically discuss the various factors on EArth (life, water, plate tectonics, etc.) that have influenced the mineralogy and lithology, and biogeochemical cycles. They decide within each small group which of the factors they believe to be dominant within each category. After ~ 20-30 minutes, they present their conclusions to the class as a whole. Discussion ensues. I guide the discussion but try to let the students do as much of the discussion leading as possible.
1_hazen_2010_evolution (Acrobat (PDF) 2.2MB Apr29 13)
Teaching Notes and Tips
You have to be very familiar with the material and circulate with the students. It helps to have a knowledgeable TA who can circulate also if the class is above 25 or so.
I don't rush this, and I let the student discussions go on for quite a while. I also let the final plenary discussion range pretty broadly.
Their performance on relevant questions in exams, their degree of engagement in the activity itself, and the response of students to further discussions involving these concepts later in the semester.
References and Resources