Modeling fossil formation using leaves, twigs, sand and water. Pour 4 inches of water in a container first. Then add 2 inches of sand. Spread twigs and leaves in a thin layer on top of the sand. What would you see in a week? Add 2 more inches of wet sand on top of leaves and twigs and let dry for 2 weeks. At the end of 3 weeks, gently break apart the layers. What do you see on the bottom and top layers of sand and in the leaves and twigs.