It is proven that the upper part and lower part just above the core of the mantle are water free but the debate is on over the portion exactly in the middle of them.

The middle portion is a mineral rich zone containing minerals like wadsleyite and ringwoodite which have the abilities to retain water. Thus the debate is over the fact that the middle portion might be holding massive amounts of water. To solve this logically, scientists carried out an experiment. They made a model similar to that of a mantle as they had the information that viscosity of the middle portion is lower as compared the upper and lower part. They made a synthetic ringwoodite which represented middle portion and bridgmanite to represent the lower mantle. Then with a dislocation technique, they measured viscosity and later added water to ringwoodite. This reduced the viscosity and the finals reports of the experiments matched the actual measurements of the real mantle.

Later the measurements reported were used to calculate the exact amount of water in the mantle. Results showed that the amount of water equalled to the expanse of Earth’s oceans.