From Snowball to Phaneorozic Earth

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Abstract
The so-called Late Proterozoic snowball Earth disappeared at the beginning of Phanerozoic time: the surface of the Phanerozoic Earth was enveloped by an ocean and oxygen-rich atmosphere, and the planet had a warm climate. We propose that this dramatic change resulted from the return flow of seawater into the mantle beginning at 750 Ma, as a consequence of the cooling of the Earth and start of the main glacial epoch. Phase relations for minerals in the system MORB + H2O and peridotite + H2O suggest that old, cold subducting oceanic slabs would transport surface water through ultrahigh-P hydrous silicates to the mantle transition zone at depths of 410-660 km. This zone could store abundant H2O, inasmuch as hydrous β and γ phases of the olivine composition may contain up to 2 to 3 wt% water. Geotherms computed for rocks of ancient subduction zones from regional metamorphic belts around the world record such a warm-to-cold transition in and below the lithosphere at 750 Ma. The runaway cooling of the Earth's i...