Evidence  is growing for the theory  that claims that the amount of water in Earth’s “transition zone” (see the graphics above) is as much as the water contained in all oceans.
Why is this important? More water in the mantle may have implications for the mechanics of the plate tectonics. I highly recommend the tutorial Khan Academy video on plate tectonics.
Effect of water on olivine- wadsleyite phase boundary in the (Mg,Fe)2SiO4 system. J. Geophys. Res. Lett. 29, 1875 (2002), , &
Solubility of water in the α, β and γ phases of (Mg,Fe)2SiO4. Contrib. Mineral. Petrol. 123, 345–357 (1996), &
Structural systematics of hydrous ringwoodite and water in Earth’s interior.Am. Mineral. 88, 1402–1407 (2003)et al.
β-Mg2SiO4: a potential host for water in the mantle? Am. Mineral. 72, 1051–1055(1987)