The boys are learning about the homosphere, which is the layer of atmosphere closest to the earth and the heterosphere, which is above the homosphere. The heterosphere (different sphere) has several layers in which different gases prodominate, which gives the heterosphere its name. We made this little lift-the-flap page by taping a white sheet of paper at the top of a sheet of manilla cardstock, leaving about an inch of the cardstock showing at the bottom. The labels are then added.
We cut out this chart of the layers of the homosphere from Considering God's Creation workbook and added to the homosphere page.