Pour one cup of plain white flower into a mixing bowl. Add water and mix the flour and water mixture until the mixture -- the glue -- takes on the consistency of watered-down pancake batter, or slightly thinner than white craft glue.
Tear a newspaper into strips about 1-inch wide. The strips can be as short or as long as you you want.
Blow up a party balloon. Place the inflated balloon in a clean mixing bowl to prevent the balloon from rolling around as you work.
Soak a strip of newspaper in the glue. Remove excess glue by sliding your fingers down the length of the strip.
Lay the soaked strip across the balloon and smooth out any wrinkles. Repeat steps 4 and 5 until the top half of the balloon is completely covered. Allow the glue to dry completely, creating paper mache.
Repeat steps 4 and 5 for a second and, if desired, third layer of paper mache. Allow the glue to dry completely between layers to prevent mold.
Remove the balloon from the paper mache. Carefully trim the edge of the paper mache to create a smooth half sphere, much like a bowl.
Knot a foot-long piece of string on one end. Use the tip of a pencil to poke a hole near the edge of the half sphere's rim. This will be the top of your model. String the end of the string without a knot through the hole to create a hanger. Secure the string with a piece of tape.
Place the half sphere open-side down on a piece of paper and trace the diameter of the sphere. Cut out the circle.
Paint the outside of the half sphere to represent one half of the Earth's surface using acrylic craft paint. You can choose any hemisphere you like to paint.
Use markers to draw the solid inner core, the liquid outer core, the mantle and the crust on the paper circle. Color and label the Earth's layers if desired.
Tape the paper circle to the open side of the half sphere with the drawn layers facing out. Hang the model.