I probably shouldn’t have baked chocolate chip cookies yesterday, what with today being one of the two biggest chocolate-buzz holidays on the American calendar. But I did.
I’ve had a lot of trouble figuring out the best recipe adjustments for high elevation. My cookies have a tendency to puff up big, and then collapse into goo. The end results look like this:
All wrinkled around the edges, and flat in the middle. In fact, it looks like something I could map:
Those are fold symbols for the wrinkles around the edge, and normal fault symbols for the places where the crust broke open to reveal the goo beneath.
And that got me thinking about how I would interpret this if it were, say, a radar-mapping image from another planet. The folds imply shortening perpendicular to the hinge lines – that is, the cookie seems to have shrunk. (The Small Human would be upset.) But the normal faults imply that the cookie stretched perpendicular to the cracks – the cookie grew. Weird. Inconsistent stories. Makes no sense.
But a structural geologist is not bothered by confusing, totally messed up
rocks cookies. This is what we live for. The next step should be to think through some possible explanations. Are the structures all the same age, or does this mountain range cookie represent two different events, superimposed? Are the old normal faults folded? Are the folds pulled apart?
Unfortunately, in this case I don’t have any good cross-cutting relationships, and the interpretation remains ambiguous. (This is where a few good zircons might save my day. Unfortunately, cookies do not contain good minerals for dating. Or maybe that should be fortunately. Zircons are hard on teeth.)
In this case, however, I know what the cookies looked like when I checked the first pan before they were ready to come out. First the cookies puffed up, and then they collapsed. While they puffed up, their surface area increased, so the cookie crust was pulled apart. When the cookies collapsed, the surface area decreased again, and the cookie crust wrinkled as the dome tried to fit itself into a pancake. (Ediacaran’s trilobites have similar features, though I suspect they don’t taste as good.)
My model doesn’t exactly explain my structures, though. When the cookie puffed up, I would expect it to crack in radial fractures, but it doesn’t – the “normal faults” are parallel to each other. I can wave my arms and say something about the local stresses being perturbed by the chips or something, but I have no real clue what was going on.
And I can’t go back and look for other features to test my models. I’ve already eaten the cookie. It may have been an imperfect modeling medium, but I bet it tasted better than the average sandbox experiment.