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
Volcanoes under pressure
18.11.2019 | Technical University of Munich (TUM)
New findings on the largest natural sulfur source in the atmosphere
18.11.2019 | Leibniz-Institut für Troposphärenforschung e. V.
Nanooptical traps are a promising building block for quantum technologies. Austrian and German scientists have now removed an important obstacle to their practical use. They were able to show that a special form of mechanical vibration heats trapped particles in a very short time and knocks them out of the trap.
By controlling individual atoms, quantum properties can be investigated and made usable for technological applications. For about ten years, physicists have...
An international team of scientists, including three researchers from New Jersey Institute of Technology (NJIT), has shed new light on one of the central mysteries of solar physics: how energy from the Sun is transferred to the star's upper atmosphere, heating it to 1 million degrees Fahrenheit and higher in some regions, temperatures that are vastly hotter than the Sun's surface.
With new images from NJIT's Big Bear Solar Observatory (BBSO), the researchers have revealed in groundbreaking, granular detail what appears to be a likely...
The Fraunhofer Institute for Manufacturing Technology and Advanced Materials IFAM in Dresden has succeeded in using Selective Electron Beam Melting (SEBM) to...
Carbon nanotubes (CNTs) are valuable for a wide variety of applications. Made of graphene sheets rolled into tubes 10,000 times smaller than a human hair, CNTs have an exceptional strength-to-mass ratio and excellent thermal and electrical properties. These features make them ideal for a range of applications, including supercapacitors, interconnects, adhesives, particle trapping and structural color.
New research reveals even more potential for CNTs: as a coating, they can both repel and hold water in place, a useful property for applications like printing,...
If you've ever tried to put several really strong, small cube magnets right next to each other on a magnetic board, you'll know that you just can't do it. What happens is that the magnets always arrange themselves in a column sticking out vertically from the magnetic board. Moreover, it's almost impossible to join several rows of these magnets together to form a flat surface. That's because magnets are dipolar. Equal poles repel each other, with the north pole of one magnet always attaching itself to the south pole of another and vice versa. This explains why they form a column with all the magnets aligned the same way.
Now, scientists at ETH Zurich have managed to create magnetic building blocks in the shape of cubes that - for the first time ever - can be joined together to...
15.11.2019 | Event News
15.11.2019 | Event News
05.11.2019 | Event News
19.11.2019 | Life Sciences
19.11.2019 | Physics and Astronomy
19.11.2019 | Health and Medicine