Mass of water in different reservoirs as a function of time (top: Earth, bottom: Mars). Before the onset of the run-away greenhouse effect, most of the water resides in the massive surface layer and in the clay mantle below. The majority of the water is dissolved into the newly formed magma ocean and core when the planets differentiate by the accretion energy. The crystallization of the magma ocean after 7 Myr leads to the release of approximately two modern Earth oceans of water on Earth, while the reduced mantle of Mars leads to outgassing of far less water.