Actvity Summary: The ocean crust is much younger than the continental crust, however both form the tectonic plates that cover the Earth. The main reason that oceanic crust does not get to be as old is due to density - tectonic plates mainly formed of oceanic crust are heavier, and so sink beneath continental crust at subduction boundaries, where it melts as it sinks, and gets recycled into the mantle. Meanwhile new crust forms at divergent boundaries, where tectonic plates move away from each other providing a space for magma to rise up, cool and harden into new crust. Diagrams are used a lot in geosciences and other sciences as a way to visualize scientific concepts, models, and theories. Learning how to understand them is critical to someone’s knowledge and skills in the real world.