Friday, July 5, 2013

Seeing Fossils



My wife and I spent part of July 4 the way Thomas Jefferson and Benjamin Franklin would have approved of: we went looking for fossils. We walked on the Quaternary alluvial bed of the Arkansas River in Tulsa. We have been there many times, but all we saw, or thought we saw, was sand, smooth stones, broken glass (some of it smoothed by abrasion), ultraviolet-bleached plastic, shopping carts, and miscellaneous embarrassing items. But this time we looked for, and therefore saw, things we had previously overlooked.

One thing we found was coal. Just a few fragments of it. We do not know if it washed down from coal deposits no longer being mined, or from piles of coal. That’s the think about alluvial deposits, especially for a major river: you know almost nothing about where they came from. And we saw a few fossils, such as this one of crinoids.


But another experience we had was the opposite of seeing what we had previously overlooked. We saw some rocks that we might have imagined to have fossils in them. Just the day before, I had examined fossil deposits along Lake Oologah north of Claremore, Oklahoma, and I saw what I thought was a fossilized stem. It was a different color from the surrounding matrix and had parallel ridges that looked like wood grain. Then I noticed that the ridges extended past the differently-colored region. I also found what looked like a weird animal fossil. What a strange shape! I’m not going to tell you what it looked like, but it was something that it most definitely could not have been. What we saw among the rocks in the riverbed were structures that we imagined might be fossils. One of them looked like stromatolite layers, with just the right waviness that could not be explained as ripple marks. Were we just imagining this to be a piece of stromatolite? And the thing that looked like a fragment of fish backbone and ribs. Well, isn’t that what we expected to find?

This brings up, again, the important point that the human mind sees what it expects to see, whether (in this case) the absence of fossils or their abundance. Once we started looking for fossils, I wanted to find at least one every ten minutes or so, in order to feel that I was having a good time. Fossils have always been a good medium for observer bias. Today we laugh at medieval people who thought that cephalopod shell fossils were actually thunderbolts turned into stone. But we are no different from those people in seeing what we expect to see. It is sort of like e e cummings who said, so whatever we lose like a you or a me it’s always ourselves we find in the sea, or in this case, the sand of a river bottom.

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