Make a Fossil at Home for DeSTEMber

Girlstart’s DeSTEMber is a month-long celebration of all things STEM, held in the last month of the year and built around the belief that STEM learning belongs in everyday life. Texas Science & Natural History Museum’s Mold and Cast activity lets elementary-aged kids make a fossil at home, just like nature does. Kids press a shell (or a sea star, toy dinosaur foot, or fish bone) into flattened clay, which represents the soft mud of an ancient seafloor. When they lift the shell out, the hollow print left behind is a mold. An adult then mixes plaster of Paris and pours it into the mold. Once it hardens, kids peel away the clay to reveal a stone-like cast of their shell. No plaster? A thick paste of flour, salt, and water works too, though it dries more slowly and gives a softer copy.

Real fossilization is rare. It takes soft mud, quick burial, and mineral-rich water at just the right time, and a natural cast takes thousands of years to form. Our plaster version shows the process in a few hours and gives families a chance to talk about how scientists learn about the past. Along the way, kids learn vocabulary like mold, cast, and replica, and what a paleontologist does. The activity also supports Texas science standards for grades 3 and 4, including fossils as evidence of past environments and the use of models. Grab some clay and a shell, and see what you can uncover this DeSTEMber!

Download the Activity Packet (PDF)