Hot magma inside (Mid-Atlantic Ridge slurry) and cold outside (Namibian rock slurry reports Snowball earth) is one contrast. The other contrast is converging (Costa Rican Accretionary Prism) and diverging (M.A.R. at Kane Fracture Zone) plates. In addition, a reminder that everything's connected by movements in space and time -- that's the "All" glaze of lighter color.
Writing describes it.