Explorers

In January the Explorers set out to create some fossils—not in the oodles of years that the normal process requires, but in mere minutes. Were they successful? Well, yes and no.

They started off by smoothing small amounts of Play-Doh into discs that fit nicely into the bottom of paper cups, and then pressing a sea shell (smeared lightly with Vaseline so that they wouldn’t stick too badly) into the Play-Doh so that an imprint of the shell was created in the squishy surface. This served as the equivalent of an original surface of mud, perhaps at the bottom of an ancient sea or in the shallows of a tide pool.

The Explorers then continued by mixing small amounts of plaster of paris. This material starts off as a thick and heavy powder, but when mixed with water it becomes a thick and heavy (and gooey) paste. Think of a Frosty from Wendy’s, and you’ll have the idea. Once it is stirred to a smooth consistency, with no remaining lumps, the mixture can be poured/scraped/otherwise convinced to leave the mixing cup or bowl. The Explorers each poured a small amount into the paper cups on top of and covering the Play-Doh, and then set the whole bit aside to harden.

This hardening process, requiring a short time for the plaster, represents the geologic time scales needed for layers of sedimentary rock to form. Remember our shell imprint in the ancient sea? If that imprint was covered by a layer of mud before it was wiped out, it then had the potential to be preserved. As more and more layers of mud, sand, silt, and clay formed atop it, burying it deeper and deeper, the layer of mud containing the imprint would slowly be pressed and cemented into solid rock—sedimentary rock, to be precise. This formation in layers is one of the best ways to identify sedimentary rocks, in fact—find a photo of the Grand Canyon to see the end result of this process on a truly grand scale.

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When the plaster is completely set (after a day or so), the cups can be peeled away and the Play-Doh scraped off to reveal—voila—nearly instant fossils. Well, we called them fossils, but in fact what the Explorers had done was create “casts” of the imprint. This is exactly what field naturalists often do to preserve animal tracks in the wild—carrying along some plaster powder and water, along with a thick paper “mold” to encircle the tracks and prevent the mixture from spreading out, is a good way to bring evidence of these tracks home with you.

So, back to the Explorers. Part one of their fossil-making activity had turned out just fine, so it was time to move on to part two. This is where we ran into some troubles.

The goal was for each student to mix up a much larger amount of plaster goo, then pour it into an aluminum baking tin, slather some Vaseline onto the bottom of their own bare foot, and press their foot into the mixture to create a fossil of their own footprint. Simple enough in theory, but the execution of the plan went awry. The problem was just that once everyone had their goo ready, it took much longer than anticipated to get the Vaseline to everyone in the group, and in the meantime everyone’s plaster was hardening much faster than expected. In the end, only a few of the students were successful in getting any sort of footprint before their mixture turned into a collection of newly-formed rocks.

A disappointment? Perhaps, but also a reminder that science activities and experiments often have a way of going in a direction entirely different from what was intended. The students found one common thread to unite them, though—they were unanimous in their agreement that the problem was Mr. Ramsey’s fault. For his part, Mr. Ramsey tried to make the claim that the “problem” was in fact a very clever attempt on his part to demonstrate how experiments can go bad, but none of the students were buying that story. In the end, though, everyone was satisfied with an assurance that we would give it another go at our next meeting, keeping in mind that we learned one very important lesson—must go faster!

ONE IMPORTANT WORD OF WARNING: When plaster of paris powder is mixed with water, a chemical reaction occurs that results in the hardened rock. One other product of that reaction is heat—a surprising amount of heat, in fact. Several of the Explorers whose plaster hardened in their mixing bowls noted how warm the bowls became. This is not a problem at all in the sort of activity we did, briefly pressing a foot (or a hand, or a finger, or whatever) into the gooey mix and then removing it. However, a number of people have been injured, and in a few cases very badly burned, by trying to use the mixture to encase a part of their body—to create a cast, in essence. NEVER, EVER “wrap” any part of someone’s body with a plaster of paris mixture!