Water reservoir detected 1 000 km below Earth’s surface

water-lower-earth-mantle

Scientists have discovered water about 1 000 km (620 miles) below the Earth's surface. The discovery suggests our planet's mantle may contain much more water, and at much bigger depths, than previously thought.

The water reservoir was found about one-third of the way to the edge of Earth's core. The presence of the water was indicated by a 90 million years old diamond spat, at a volcano situated near the São Luíz river in Juina, Brazil.

According to Steve Jacobsen, at the Northwestern University in Evanston, Illinois, the discovery implies an existence of a much bigger water reservoir on Earth than previously thought.

A sealed-off inclusion of the diamond contains minerals which were trapped when it was being formed. The examination carried out by the infrared microscopy revealed the presence of hydroxyl ions, associated with the presence of water. The inclusion made of a ferropericlase mineral allowed the researchers to deduce the depth of diamond's formation.

The mineral contains iron and magnesium oxide and is capable of absorbing chromium, aluminum, and titanium at very high temperatures and pressures usual for the planet's lower mantle. These components have separated from the mineral itself, in a process which happens as the diamond edges up through shallower regions. However, their presence indicates the diamond must have been formed in a much more dynamic environment, typical of the Earth's lower mantle.

“Based on the composition of the trapped mineral, we speculate that the depth was around 1 000 km (621.4 miles).  This is the deepest evidence for water recycling on the planet. The big take-home message is that the water cycle on Earth is bigger than we ever thought, extending into the deep mantle.” said Jacobsen.

The researchers have found large amounts of water mixed with rocks previously, at depths of  about 600 km (372.8 miles) from the surface. However, the scientists are still not sure how much water is down there exactly, and how was it formed. One theory suggests the water could have been present in the mantle for more than 90 million years, and it may have settled down through the process of sedimentary oceanic crust burrowing when primitive tectonic plates moved against each other.

“Water clearly has a role in plate tectonics, and we didn’t know before how deep these effects could reach. It has implications for the origin of water on the planet,” explained Jacobsen.

The new study implies the cycling of subducted materials, and the scientists hope further research will aid them in understanding how our planet recycles itself and provide more information about how the Earth's oceans and atmosphere formed.

Reference:

  • "Evidence for H2O-bearing fluids in the lower mantle from diamond inclusion" – M. Palot, S.D. Jacobsen, J.P. Townsend, F. Nestola, K. Marquardt, N. Miyajima, J.W. Harris, T. Stachel, C.A. McCammon, D.G. Pearson – Lithos (2016) – http://dx.doi.org/10.1016/j.lithos.2016.06.023

Featured image credit: Andrew Campbell (Flickr-CC)

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