A 3D model of the earth can show the external structures of land and water in addition to the internal structures. Choose the size of the model and the specific details you desire. The external detail can show only land and water or can include details of water flow, temperature and air currents if you wish.
Mix one part flour with two parts water in the mixing bowl to make paper mache paste. Dip the newspaper strips in the paper mache and cover the styrofoam ball with a thick layer of newspaper. Set aside to dry overnight.
Tie a string around the centre of the ball. Trace along the string to create the equator. Remove the string. Cut through the entire ball at the equator to create the two halves of the Earth.
Place the point of the compass in the centre on the flat side of one half of the Earth. Extend the pencil 1/3 of the distance to the outside edge. Draw a circle. Extend the pencil to 2/3 the distance to the outside edge and draw another circle. Remove the compass. Paint the centre circle yellow to represent the inner core of the planet. Paint the next ring orange to represent the outer core. Paint the final section red to represent the mantle. Repeat the process with the second half of the model. Allow the paint to dry.
Insert toothpicks vertically around the edge of the mantle on one side of the model so approximately ½ of the toothpick is visible. Glue in place as necessary. Insert the other half of the model onto the toothpicks so the earth model becomes a complete ball shape. Leave a small space between the halves to allow easy opening of the model when needed.
Draw the general outlines of the seven continents in their correct locations on the globe. Paint the continents brown, the water blue and the polar caps white. Label as desired. Mold clay into a small bowl shape and glue it to a wood base. Set the Earth model into the bowl shape of the base to display it.
Sand the edges of the model after it is cut in half to form smoother edges.