A more watery lower mantle would churn faster.
Five times as much water as in all the world’s oceans may lurk deep below its surface.
Geologists have divined water where you might least expect it: 1,000 kilometres below the Earth’s surface. Here, rocks heated to over 1,000 oC and squeezed under high pressures may harbour around five times as much water as in all the world’s oceans. This could give clues to how the Earth formed and how it behaves today.
Between 650 and 2,900 km below the Earth’s surface hot, compressed minerals surround the planet’s iron-rich core. Called the lower mantle, this material may hold up to 0.2 per cent of its own weight in water, estimate Motohiko Murakami, of the Tokyo Institute of Technology in Japan, and colleagues1.
Water would lower the melting point of rocks in the lower mantle and increase their viscosity. Over millions of years, the mantle churns like a pan of hot soup. This moves the tectonic plates and mixes the mantle’s chemical components. A more viscous mantle would churn faster.
The take-up of water by minerals in the lower mantle might also affect the ease with which tectonic plates sink deep into the Earth. As the plates descend, heat up and become squeezed, the water that they release might soften the surrounding mantle and ease their passage.
There is already thought to be several oceans’ worth of water slightly higher in the mantle, at a depth of around 400-650 km. This region is called the transition zone, as it is between the upper and the lower mantle.
The lower mantle’s minerals can retain about a tenth as much water as the rocks above, Murakami’s team finds. But because the volume of the lower mantle is much greater than that of the transition zone, it could hold a comparable amount of water.
"The findings will boost the debate about how much water is locked away in the mantle," says geologist Bernard Wood of the University of Bristol, UK. Until now, he says, "most people would have argued that there isn’t much water in the mantle". A similar study two years ago concluded that there isn’t much water down there at all2.
Taking on the mantle
Murakami’s team mimicked the lower mantle in the laboratory. They studied the three kinds of mineral thought to make up most of the region: two perovskites, one rich in magnesium, the other in calcium, and magnesiowustite, a mixture of magnesium and iron oxides.
To recreate the its furious conditions, the researchers used a multi-anvil cell. This heats materials while squeezing them between hard teeth. Having baked the minerals at around 1,600 oC and 250,000 atmospheres, the team measured how much hydrogen the rocks contained using secondary-ion mass spectrometry. This technique blasts the material with a beam of ions and detects the ions sprayed out from the surface.
Any hydrogen in the rocks presumably comes from trapped water, an idea that other measurements support. The researchers found more hydrogen than previous experiments had led them to expect.
PHILIP BALL | © Nature News Service
Predicting unpredictability: Information theory offers new way to read ice cores
07.12.2016 | Santa Fe Institute
Sea ice hit record lows in November
07.12.2016 | University of Colorado at Boulder
Physicists of the University of Würzburg have made an astonishing discovery in a specific type of topological insulators. The effect is due to the structure of the materials used. The researchers have now published their work in the journal Science.
Topological insulators are currently the hot topic in physics according to the newspaper Neue Zürcher Zeitung. Only a few weeks ago, their importance was...
In recent years, lasers with ultrashort pulses (USP) down to the femtosecond range have become established on an industrial scale. They could advance some applications with the much-lauded “cold ablation” – if that meant they would then achieve more throughput. A new generation of process engineering that will address this issue in particular will be discussed at the “4th UKP Workshop – Ultrafast Laser Technology” in April 2017.
Even back in the 1990s, scientists were comparing materials processing with nanosecond, picosecond and femtosesecond pulses. The result was surprising:...
Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...
A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.
Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...
In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.
“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...
16.11.2016 | Event News
01.11.2016 | Event News
14.10.2016 | Event News
09.12.2016 | Life Sciences
09.12.2016 | Ecology, The Environment and Conservation
09.12.2016 | Health and Medicine