Get My Drift?

Yesterday we did three activities related to plate tectonics: making a
model of continental motion and generating predictions from it;
locating earthquakes; and radioisotope dating of rocks.

In the first activity, I gave students cutouts of the continents.
(The best way to find these is by googling terms related to this
activity; you can't just print a world map because of the distortion
inherent in most projections.)  The cutouts were on their desks as the
students filed in, so it was interesting to see what the students did
without any instructions: mostly arrange them as they are now rather
than try to put them together like a puzzle.  But it only took a small
hint to get them assembling the puzzle.  Once each group settled on a
way of fitting the continents together, I had them glue the model to
one side of a handout I had prepared.  On the other side they were
instructed to make four specific predictions about what would be
observable if this model were true.  I had to drop some major hints,
but the groups did eventually come up with the same four major
categories: (1) fossils on once-adjacent pieces of land should be the
same even though they are now very far apart; (2) living creatures on
once-adjacent pieces of land should be similar (making allowance for
evolutionary changes and for especially mobile animals such as birds
to be excluded from this analysis; (3) an expanding ocean floor should
be young in the middle where it spreads apart, and progressively older
near the continents (some groups put more emphasis on finding an
identifiable mid-ocean feature, but it's basically the same idea); (4)
once-adjacent pieces of land should have very similar older rock
layers even though they are now very far apart.  One thing no one got
even though I mentioned GPS is that we should be able to measure the
distance between, say, North America and Europe increasing very
slightly each year (it is, by a few centimeters per year).

I had planned for this to be iterative.  In my original plan the
groups were to make a very specific prediction such as "fossils found
in this part of Antarctica match the fossils in this part of
Australia", and then I would look that up quickly (to prevent
computers from being a distraction), and then after seeing how all
four predictions went they would make a better model on a new sheet of
paper (I brought lots of continent cutouts).  But the initial puzzle
assembling took much, much longer than I anticipated.  Some groups
took a lot of time to trim their rough-cut continent cutouts in
exquisite detail; others rearranged theirs many times; others just
didn't focus as much as I would have liked.  So we didn't go through
another iteration.  But one lesson that was clear to me at least is
that although South America fits nicely into Africa, almost nothing
else matches that clearly.  At some point you have to guess (this is
clear when comparing the different guesses of the different groups),
and at that point you have to look for fossil evidence to verify or
falsify your guess.  That whole process is what science is really all
about!

In the time left before break, I asked the students to guess why the
continents move.  They had a lot of crazy theories, but I steered it
back to what we had learned last week: the core of the Earth is hot,
heat flows to areas of lower temperature, and it can flow through
radiation, conduction, and/or convection.  We talked about how each of
these might or might not apply in this case, and figured out that
convection is well suited to transporting heat through the mantle,
which is fluid although not really molten.  Once we got this all into
a diagram with convection loops in the mantle, it was clear that this
was a very plausible mechanism for making continents move. 

This whole activity took 45 minutes, and as I mentioned I probably
should have budgeted much longer, and/or come up with ways to save
lots of time on the puzzle-assembly.  Devoting time to verify or
falsify specific predictions and come up with a better model would
have been a great illustration of the process of science.  Maybe it
should be a homework.  But, apart from this reservation, I think it's
a great activity.