The scientists discovered evidence of water hundreds of kilometers deep. An international research team led by a Goethe University professor analyzes diamond inclusions. The boundary layer between the upper and lower mantles of the Earth is known as the transition zone (TZ). It is located between 410 and 660 kilometers (between 255 and 410 miles) under the surface. The olive-green mineral olivine, commonly known as peridot, which makes up around 70% of the Earth’s upper mantle, changes its crystalline structure at the extreme pressure of up to 23,000 bar in the TZ. At a depth of around 410 kilometers (255...