  Magma oceans are a common result of the high degree of heating that occurs
during planet formation. It is thought that almost all of the large rocky
bodies in the Solar System went through at least one magma ocean phase. In this
paper, we review some of the ways in which magma ocean models for the Earth,
Moon, and Mars match present day observations of mantle reservoirs, internal
structure, and primordial crusts, and then we present new calculations for the
oxidation state of the mantle produced during the magma ocean phase. The
crystallization of magma oceans likely leads to a massive mantle overturn that
may set up a stably stratified mantle. This may lead to significant delays or
total prevention of plate tectonics on some planets. We review recent models
that may help partly alleviate the mantle stability issue and lead to earlier
onset of plate tectonics.
