Teaching Historical: Marching through time

OK, so texts are too detailed.  But surely to teach earth history you need to tell how the crust was made, how continents moved about, how archea led to prokaryotes [if you still like that term] led to eukaryotes, etc. So you have to start things at the beginning and move forward, right?

Well, GG disagrees.  Here is why: (1) This isn’t how we decipher a geologic history; instead we unravel the recent stuff and that gives us some clues about the older stuff. (2) We tell students that “the key to the past is the present” and then start them on stories of a planet with an unbreathable atmosphere with little or no life and no continents. Why should they believe any of this?  How does the present inform that past?

So there are some different options once you pitch out the need to explain every last detail and the need to tell the story from the start.  First, pick out elements of the past that illustrate the grand themes you are interested in.  These can be fairly concrete things like proxies and extinction and more diffuse concepts like feedbacks between geosphere, biosphere and atmosphere. Start with the stuff that is pretty familiar.  So, for instance, the course GG teaches starts with figuring out when the next earthquake on the San Andreas fault is likely to occur, which requires knowing when the past few earthquakes were.  This builds off of the death and destruction theme common in physical geology and is of more than passing interest to many students. And, since we are dealing with calendar years and a modern landscape, we can see how the present informs the past because this is hardly a distant past that operates under strange rules.

Adopting this approach means that as you look farther back, you start to see things that simply aren’t part of the world today: mastodons, dinosaurs, an absence of glaciers, Pangea, an absence of animals on land, detrital pyrite, banded iron formations. As you encounter these, you try to see how to explain them, and this leads you to the eventual conclusion that that hopelessly strange Precambrian world is really based off of what we see today.

OK, now some of you noted that GG starts with the next earthquake….but when do we talk about how to do historical geology?  That will be up next….


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