According to a new study published in Nature Geoscience, a vast reservoir of water is located in the so-called transition zone between the upper and lower mantle at a depth of 410 to 660 kms.
Key points
- The new revelation is based on a diamond recently unearthed in a diamond mine in Botswana which is riddled with flaws containing traces of ringwoodite, ferropericlase, enstatite, and other minerals that suggest the diamond formed 660 kilometers (410 miles) below Earth’s surface.
- Natural diamonds are generally formed in the mantle at depths between 150 to 250 kms, but a few may come from much deeper down.
- The transition zone between the Earth’s upper and lower mantle contains considerable quantities of water, according to the new study.
- The research team analyzed the rare diamond below the Earth’s surface using techniques including Raman spectroscopy and FTIR spectrometry.
- The study confirmed something that for a long time was only a theory, namely that ocean water accompanies subducting slabs and thus enters the transition zone. This means that our planet’s water cycle includes the Earth’s interior.
- The analyses revealed that the stone contains numerous ringwoodite inclusions — which exhibit a high water content.
- The research group was able to determine the chemical composition of the stone. It was almost exactly the same as that of virtually every fragment of mantle rock found in basalts anywhere in the world. This showed that the diamond definitely came from a normal piece of the Earth’s mantle.
- The occurrence of ringwoodite together with the hydrous phases indicate a wet environment at this boundary, write a team of researchers led by mineral physicist Tingting Gu of the Gemological Institute of New York and Purdue University.
- Ringwoodite is a high-pressure phase of Mg2SiO4 (magnesium silicate) formed at high temperatures and pressures of the Earth’s mantle between 525 and 660 km.
