sciencehabit writes "A 40 micrometer crystal trapped inside a diamond unearthed by magma in Brazil could help settle a long-standing debate about the amount of water in Earth's mantle. Spectroscopic analysis reveal that the crystal contains hydrogen-oxygen bonds, which suggests it's composed of at least 1.4% water. The place where the diamond was produced--Earth's lower mantle--may not be typical of the entire lower mantle, but if it is then there could be a lot of water down there. This would be important, as changes in the temperature in the mantle could cause it to expel highly pressurized steam, which could lead to volcanic eruptions."
We warn the reader in advance that the proof presented here depends on a
clever but highly unmotivated trick.
-- Howard Anton, "Elementary Linear Algebra"