Teaching Historical: The how-to manual
A really important part of historical geology is understanding how on earth this is done. After all, we don’t simply whisper to rocks, “what was it like when you were formed?”
In classes where we went through Steno’s Laws and radiometric dating and cladistics and all that first, students seemed to have difficulty in recognizing when these tools were employed within the “march through time.” Also, it meant that they focused on all the dates and things in the march through time, which frankly isn’t really what we care about the most.
So we’ve tried something different: we start right in on the march through time and when we encounter things we can’t figure out with the tools we have already, we need to learn about new tools. Students see a motivation for the tool right off the bat. It doesn’t come out of thin air, there isn’t the “gee, what is this good for.” And we make the march through time less about exactly what happened and more about both the tools and themes that we really want to convey.
So, for instance, to determine the last few earthquakes on the San Andreas we find ourselves in a trench looking at fault traces. To interpret this we need two tools: an understanding of crosscutting relationships in sedimentary rocks and carbon-dating. So off we go to learn Steno’s Laws and try to apply them to our trench and then calibrate the relative dates using carbon dates. As part of this, we also see that not everything is datable (an important concept) and thus that there is uncertainty in such interpretations (students loathe uncertainty). A small side benefit comes as we move farther back and cannot use carbon dating, because students often walk in the door thinking you can carbon date practically anything.
Of course once you’ve chopped up the course like this, the textbook is a mess: reading assignments are fractions of pages across multiple chapters.
Next up, perhaps, will be a discussion of some possible concepts that maybe should be the focus of a historical geology class…