Fossils

Sedimentary Rock

Wind and water break and wear pieces off of rocks. Water and wind also move small pieces of rocks and minerals. When these pieces get into a body of water they settle at the bottom. As time passes, these pieces are compressed by the weight of more sediment on top of it. Minerals seep in and cement the small pieces of rock together. This is a way that sedimentary rocks are formed.

Fossils

If the remains of a plant or animal are buried in this sediment before the remains have a chance to decompose, they will be trapped in the rock. Minerals will slowly replace the animal remains and leave behind a fossil.

Making Fossils

Put some play doh in the bottom of a plastic container. Stick an item that you want to make a fossil of in the play doh and then take it out. Poor Plaster of Paris over the play doh. This blog has great mixing instructions with a video. Basically you need 2 parts dry plaster to 1 part water. Make sure you wear something over your mouth so you don’t breath the powder in and wear goggles and gloves. DO NOT put the extra mix down the drain, just throw out the containers you used to mix it up in. I saved a bunch of yogurt containers for this so I could just pitch them out when I was done. Let the Plaster of Paris set for 24-72 hours. We made these on a Thursday and demolded them on a Monday. Using colored play doh gave the fossils a really interesting look without doing anything extra to them. They look a bit plain if you use only white doh, but you can paint them if that is what you use.

You can use any small items to make prints in the play doh. I brought in some shells and beads.

Containers with play doh at the bottom and Plaster of Paris poured on top.

Fossil Record Jell-o

The next week we discussed fossils in layers of rock. Geologists use the order of rock layers to understand events from the distant past. When sedimentary rock layers form, more and more sediment builds up on top, so the lowest layer is at the bottom. Fossils are found in layers of sedimentary rock. Biologists use this information to see how life has changed over time. The fruit represents different animal fossils and the different colors of Jell-o represent different layers of sedimentary rock. I asked the kids to determine which fossils (fruit) and layers were older and which animals (fruit) lived at the same time.

Here you can see the top layer that has peaches, pineapple rings and cherries.