Teaching Historical: The Big Ideas

OK, a lot of what has preceded this has been focused on the mechanics of the typical intro level historical geology class.  What are the big picture items that students should come away with?

At the broadest level, they are somewhere in the realm of knowing how we learn of the earth’s history from the rock record, knowing of the great changes in the earth over its history. Different instructors are apt to pick different aspects; one of our faculty didn’t include life history at all in their version of the class.  Courses often veer towards elements of geologic history evident in the vicinity of where the class is taught, so the Laramide is important in Colorado while the Acadian orogeny might merit more attention in New England. A less obvious element is to know how the different components of the earth system interact (solid earth changes affecting climate affecting life etc.).

A couple things strike GG as pretty essential for non-majors to understand.  One is the use (and potential abuse) of proxies.  There is no doubt that a full and rich understanding of proxy calibrations and errors is well beyond a typical intro class, but recognizing how geologists come to constrain elements of the geologic past–and how obtaining those constraints can be limited–is a piece of information that would better inform discussions of, for instance, how climates were different in the geologic past.

A second idea is the ability of the geologic record to inform us of long-term impacts of human activities independent of models [but usually not independent of proxies]. Right now, the Paleocene-Eocene Thermal Maximum (PETM) stands out as a shining example: pump carbon into the atmosphere and watch the ocean grow acidic and lead to marine extinctions, see it take more than 80,000 years for that carbon to get sequestered again and you gain some perspective on human carbon emissions.  Or take the increasingly strong evidence that the rate of climate change dictates extinctions more than the overall magnitude: the long increase in temperature through the Paleocene had less of an overall impact than the sudden rise with the PETM.

A third is the way that the different components of the earth system interact. Probably the classic one is the continued equable climate of Earth: even with a dim Sun the earth had liquid water on the surface.  Removal of carbon from the atmosphere by both organic and inorganic means has been essential.  Snowball Earth hypotheses illustrate this nicely (even if you don’t fully buy them). There is a good case to be made that the development of hard parts arose as the oceans grew richer in carbonate caused by massive erosion of continents prior to the Cambrian.

There are other ideas that might matter as much: the use of the historical record to anticipate disasters as diverse as landslides to supervolcanoes to meteorite impacts. Locating mineral resources is another valid topic. These are both pretty traditional. The concept of feedbacks, especially in the climate system, is a challenge for many students yet essential to understand how small changes in some climate elements can produce big changes in global climates.

What matters least?  Probably all the gory details in between.


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