CREEPING FLOW: This figure shows results of a computer simulation of convection in the Earth's mantle. Creeping flow in this solid, rocky layer of the Earth drives geological activity such as earthquakes and volcanos on the Earth's surface. The computer simulation shows the results of thermal interaction between the Earth's mantle and its molten iron outer core over about 920 million years. Heat from the core creates hot "plumes" of upwelling material (red); cold downwellings (blue) simultaneously sink through the mantle. The red "streaks" represent the paths of plumes of hot material over time; forks in these streaks show plumes merging together. The calculations and image are by graduate student Nancy Montague and geology professor Louise Kellogg.