Compare the picture of earth's layers to your marshmallow. You can see how the earth and marshmallow are similar. They both have a center core that is red hot. The middle is also mushy and soft just like the material that makes up the earth's mantle. The thin outside layer around the marshmallow was a hot liquid but became became a thin solid surface when it cooled just like the earth's crust.
Students draw a picture of the earth's layers and label the core, mantle, and crust.