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I was of the notion that as we get deeper into the Earth, it gets hotter and hotter. If so, how can there be huge oceans (they seem bigger than our Pacific) exist at such a place? If so, what are the possible implications of this discovery in shaping our understanding of the planet? I'm very curious to find out.

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marked as duplicate by arkaia, Peter Jansson, Semidiurnal Simon, senshin, DavePhD Jun 20 '14 at 17:41

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I am going to assume that you are referring to recent new stories with titles like "Rare Diamond Confirms That Earth's Mantle Holds an Ocean's Worth of Water" (Scientific America).

These articles are referring to research published in Nature: Pearson, D. G. et al. (2014). The researchers found an inclusion of ringwoodite inside a diamond. Here is a quote from the Nature article about the paper...

Using infrared spectroscopy, Pearson’s team found that its tiny fleck of ringwoodite contained about 1% water by weight. “That may not sound like much,” Pearson says, “but when you realize how much ringwoodite there is, the transition zone could hold as much water as all the Earth’s oceans put together.”

This doesn't mean that there is a liquid ocean of water within the transition zone. There are minerals that are considered "hydrated" because they contain hydroxide ions. Examples of these are the serpentine group and micas.

Ringwoodite can contain hydroxide ions within its structure, and these ions are the "water" that was measured. If you were to lower the pressure, and increase the temperature, the water would be liberated from the mineral. The point is that there are not huge oceans of liquid water within the mantle of the Earth; the water is locked up in the structure of certain minerals.

There are interesting implications from this research discussed in the Nature News article about the research.

Nature News Article

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    $\begingroup$ Yes it is one more small step in what might be a revolution in our understanding of the mantle. It isn't a uniform convecting bulk of ultramafic silicate: It is heterogeneous in composition and contains lots of "interesting stuff" (eg. HO, the carbon in diamonds, and the fluorine inferred from my Laki question). $\endgroup$ – winwaed Jun 17 '14 at 0:47

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