Why is liquid water necessary for plate tectonics?

In short, there may be no tectonic plate activity at all in the absence of liquid water. Elaborated : A critical part of the Wilson Cycle, and of Plate Tectonics as a whole, is the initiation of subduction. read more

One thing water does for plate tectonics is lower the melting point of a descending plate. This tends to favor melts with a higher silica ratio, because they have a lower melting point. This is why the continents eventually formed. read more

Percolation of water from the surface can be the main mechanism supplying water to the upper parts of the lithosphere. This implies that liquid water can be crucial for maintaining plate tectonics. On the other hand, the surface temperature is above the freezing point because of the greenhouse gases such as carbon dioxide. read more