Dig Those Fossils

I brushed away sand from a darkish piece of bone, and slowly uncovered the jaw and teeth of a cute little 3-toed horse from 18 million years ago.

No one had seen this creature for all that time, or touched its remains. For 18 million years, it was buried in this earth, silent, unrevealed.

There's no feeling like that. Nothing in the world compares.

The jawbone was lying on its side. The teeth showed to my left, my "west," the front teeth to my "north." That meant the other side of the jaw might be buried directly underneath this one.

Since these old bones, buried in damp soil, can be quite fragile, we need to be careful when uncovering something interesting. This one was good enough that it should be prepared to go back to the lab for those careful pros to finish uncovering, cleaning, and preserving it for the museum.

Which meant it needed a plaster jacket.

At most sites where non-professional volunteers are allowed to help dig, a plaster jacket means you're - courteously - shoved aside, and the scientists or technicians present take over. Here at the Fossil Farm, there are so many good things to get jacketed, and the volunteers usually experienced enough, that we get taught to do our own. Closely supervised, of course.

This is my first plaster jacket. I'm a little giddy. I catch a buddy nearby ducking his head, hiding his grin. I don't mind a bit. He remembers this feeling, I think. Ha! I'm about to lose my plaster cast virginity.

Erika comes to instruct me, bringing a plastic museum cast of this jawbone to show me what it looks like. See the model of a jaw here? You can estimate how far the fossil extends under the soil. Dig a trench a couple inches away from the edges of the bones. Dig away from the bone, point your tools outward so you don't accidentally crack the dirt or bone. Go straight down for now, don't undercut. Go down far enough to make a mound of earth that will contain the whole jaw. Call me when you're done with that.

Okay! Now we're ready to undercut just a little bit. Just enough to give us a little overhang, to lift it out when we're done.

There's a box of fancy plaster rolls, gauze permeated with plaster, the kind they use to put a cast on a broken arm. This is something I'm comfortable with: the backyard bricklayer in me recognizes *Mud* when she sees it.

We put a plaster roll in a bucket of water: just long enough to wet it through, then squeeze it a bit just to mix it - don't squeeze the plaster out! - and unroll it around the mound of earth holding the jawbone. Go quickly, it sets up fast. Smooth out the wrinkles and air bubbles. Don't worry, we have more, this will take two or three rolls.

The first roll goes around the perimeter of the mound, holding it all together. When that's done I feel a sense of relief. It can't fall apart now. It's safe. My pretty little jawbone is safe.

The next roll goes over and over the top, twist the roll after each pass, smooth it out.

This is fun!

After three rolls, we're done. I'm beaming. The Curator - the scientist running the dig - gently tells me I'm a little punchy, go take a break. I agree.

My first plaster cast. I race up the stairs into the pole barn to tell Laurie, the cook. She gets a kick out of seeing us get all excited about this stuff. She's another backyard bricklayer, and grins at how I'm smeared with bits of plaster from head to toe.

Once the plaster jacket sets, we'll write the *Magic Words* on it with a waterproof marker. The square it came from, the date and my name and all that. I feel famous! Then, we'll lift it out and bring it up the stairs into the pole barn, where it gets carefully placed with the other plaster jackets, to go back to the museum at the end of the dig. Except, since this is the first jacket of this dig, it goes all by its smiling self.

Days like this are why I go on fossil digs.