Homemade Fossil Dig

Fossils are what lead me into my science career, and I still enjoy finding them. If you live near a place where you can dig for real fossils, you should definitely give it a try. If you do not have a fossil site nearby, you can simulate the experience with this simple activity.

You will need:

  • sand
  • plaster of paris
  • several objects to be "fossils." These can be shells, bones, pieces of wood, etc.
  • a smooth sided, disposable, plastic container. I like using a large, plastic cup.
  • a mixing bowl
  • bamboo skewers or toothpicks

Put enough sand into the cup to fill it 3/4 of the way full. Fill it the rest of the way with dry plaster. Pour the sand and plaster into the mixing bowl and stir it around to mix it.

Put about an inch of the mixture back into the cup. Drop in one or two "fossils" and then add enough of the mixture to cover them. Add another "fossil" and then more mixture. Keep doing this until your container is full.

Now your "fossils" are buried, but the "rock" is not very hard. That is why we added the plaster. Pour enough water into the cup to get the sand wet. You want it to soak all the way down to the bottom of the cup, not just wet the top layer.

Once the sand and plaster mixture is wet, let the container sit overnight. The next day, the sand mixture should have hardened into a rock-like substance. Turn the container upside down and tap it firmly a few times. The "rock" should slide out.

Now that you have your "fossils" embedded in "rock," we want to get them out again. When you are digging real fossils, the rock is often as hard or harder than the fossils. This means that you must be very careful as you dig, so you do not damage the fossil. Paleontologists use a wide range of digging tools. Much of the digging is done with small, delicate tools, ranging from picks like the dentist uses to clean your teeth, pointed splints of bamboo, or hammers and chisels, depending on the kind of rock that surrounds the fossil. Our "rock" is similar to a soft sandstone, so we will use bamboo skewers or toothpicks to scrape away the rock. Dig slowly and carefully to be sure that you do not miss anything or damage your specimens. Depending on how hard your "sandstone" is, it may take you anywhere from a few minutes to a couple of hours to excavate your finds.

You can make this exercise as realistic as you want. You can add a bit of tempera paint to add color to the sand mixture. Adding less plaster will make the "rock" softer, while more plaster will give you more of a challenge. For a real challenge, press a turkey or chicken leg bone into some modeling clay to form a mold. Mix some plaster according to the directions on the package and pour it into the mold. When it has hardened, remove it and then break it into several pieces. Let the pieces dry overnight and then bury them in the sand/plaster mixture. Since they are about the same hardness as the surrounding "rock," you will have to dig very carefully. When you have recovered all the pieces, see if you can put them back together.

For even more fun, you and a friend can make a cup of "fossils" for each other. It is much more fun if you do not know what to expect. The thrill of discovery is one of the things that makes paleontology so much fun.

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