The basic knowledge needed about convection is simple, but it took almost two decades to analyze it. The simple side can be described like that: The plastic mantle expands when heated, flows upwards, cools and flows to the sides, and eventually sinks down again. The two sides of the convection unit have equal size, and the flow compared to the rotation plane of the Earth is of equal height and breadth. The system is therefore composed of convection rolls. The complex side is described like that: To learn about the various implications of this process within the entire mantle of Earth, the geology of Iceland works as a window making a detailed analysis possible. Here you find some of the results of that analysis.