The Earth's Magnetic field is powered by Quartz Crystals

Scientists are reporting unexpected discoveries about Earth's core. The findings include insights into the source of energy driving Earth's magnetic field, factors governing the cooling of the core and its chemical composition, and conditions that existed during the formation of Earth. The Earth's core consists mostly of a huge ball of liquid metal lying at 3000 km beneath its surface, surrounded by a mantle of hot rock. Notably, at such great depths, both the core and mantle are subject to extremely high pressures and temperatures. Furthermore, research indicates that the slow creeping flow of hot buoyant rocks -- moving several centimeters per year -- carries heat away from the core to the surface, resulting in a very gradual cooling of the core over geological time. However, the degree to which the Earth's core has cooled since its formation is an area of intense debate amongst Earth scientists.

In 2013 Kei Hirose, now Director of the Earth-Life Science Institute (ELSI) at the Tokyo Institute of Technology (Tokyo Tech), reported that the Earth's core may have cooled by as much as 1000 degrees Celsius since its formation 4.5 billion years ago. This large amount of cooling would be necessary to sustain the geomagnetic field, unless there was another as yet undiscovered source of energy. These results were a major surprise to the deep Earth community, and created what Peter Olson of Johns Hopkins University referred to as, "the New Core Heat Paradox," in an article published in Science. Core cooling and energy sources for the geomagnetic field were not the only difficult issues faced by the team. Another unresolved matter was uncertainty about the chemical composition of the core. "The core is mostly iron and some nickel, but also contains about 10% of light alloys such as silicon, oxygen, sulfur, carbon, hydrogen, and other compounds," Hirose, lead author of the new study to be published in the journal Nature. "We think that many alloys are simultaneously present, but we don't know the proportion of each candidate element."

Now, in this latest research carried out in Hirose's lab at ELSI, the scientists used precision cut diamonds to squeeze tiny dust-sized samples to the same pressures that exist at the Earth's core. The high temperatures at the interior of the Earth were created by heating samples with a laser beam. By performing experiments with a range of probable alloy compositions under a variety of conditions, Hirose's and colleagues are trying to identify the unique behavior of different alloy combinations that match the distinct environment that exists at the Earth's core. The search of alloys began to yield useful results when Hirose and his collaborators began mixing more than one alloy. "In the past, most research on iron alloys in the core has focused only on the iron and a single alloy," says Hirose. "But in these experiments we decided to combine two different alloys containing silicon and oxygen, which we strongly believe exist in the core."

The researchers were surprised to find that when they examined the samples in an electron microscope, the small amounts of silicon and oxygen in the starting sample had combined together to form silicon dioxide crystals  -- the same composition as the mineral quartz found at the surface of the Earth.

"This result proved important for understanding the energetics and evolution of the core," says John Hernlund of ELSI, a co-author of the study. "We were excited because our calculations showed that crystallization of silicon dioxide crystals from the core could provide an immense new energy source for powering the Earth's magnetic field." 

The additional boost it provides is plenty enough to solve Olson's paradox. The team has also explored the implications of these results for the formation of the Earth and conditions in the early Solar System. Crystallization changes the composition of the core by removing dissolved silicon and oxygen gradually over time. Eventually the process of crystallization will stop when then core runs out of its ancient inventory of either silicon or oxygen.

"Even if you have silicon present, you can't make silicon dioxide crystals without also having some oxygen available," says ELSI scientist George Helffrich, who modeled the crystallization process for this study. "But this gives us clues about the original concentration of oxygen and silicon in the core, because only some silicon:oxygen ratios are compatible with this model."

Our planet may be blue from the inside out. Earth’s huge store of water might have originated via chemical reactions in the mantle, rather than arriving from space through collisions with ice-rich comets. This new water may be under such pressure that it can trigger earthquakes hundreds of kilometres below Earth’s surface – tremors whose origins have so far remained unexplained. That’s the upshot of a computer simulation of reactions in Earth’s upper mantle between liquid hydrogen and quartz, the most common and stable form of silica in this part of the planet.

“This is one way water can form on Earth,” says team member John Tse at the University of Saskatchewan in Canada. “We show it’s possible to have water forming in Earth’s natural environment, rather than being of extraterrestrial origin.”

The simple reaction takes place at about 1400 °C and pressures 20,000 times higher than atmospheric pressure as silica, or silicon dioxide, reacts with liquid hydrogen to form liquid water and silicon hydride. The latest work simulates this reaction under various temperatures and pressures typical of the upper mantle between 40 and 400 kilometres down. It backs up previous work by Japanese researchers who performed and reported the reaction itself in 2014. 

“We set up a computer simulation very close to their experimental conditions and simulated the trajectory of the reaction,” says Tse. But in a surprise twist, the simulation showed that the water forms within quartz but then can’t escape and so the pressure builds up.

“The hydrogen fluid diffuses through the quartz layer, but ends up forming water not at the surface, but in the bulk of the mineral,” says Tse. “We analysed the density and structure of the trapped water, and found that it is highly pressurised.”

According to the simulation, the pressure could reach as much as 200,000 atmospheres. “We observed the water to be at high pressure, which might lead to the possibility of induced earthquakes,” says Tse. The quakes could be triggered as the water finally escapes from the crystals. “However, further research is needed to quantify the amount of released water needed for triggering deep earthquakes,” says Tse. Other researchers said it was plausible that this water caused deep quakes. “These results provide important insights into the reactions between quartz and hydrogen at high pressures,” says John Ludden, executive director of the British Geological Survey. 
“The formation and release of overpressured water may be a significant trigger in the deep lithosphere for ultra-deep earthquakes, sometimes located well below the crust and in the more rigid parts of deep continental plates.”

The findings may also inform how our planet got its water to start with. Studies over the past few years have found evidence of several oceans’ worth of water locked up in rock, as far down as 1000 kilometres, questioning the assumption that water arrived from space after Earth’s formation. A study published this week, for example, based on isotopes from meteorites and Earth’s mantle, also found that water is unlikely to have arrived on icy comets after Earth formed, as has long been assumed. Instead, all this research seems to suggest that much of our planet’s water may have come from within – although no one yet knows exactly how much.“As long as the supply of hydrogen can be sustained, one can speculate that water formed from this process could be a contributor to the origin of water during Earth’s early accretion,” says Tse. “Water formed in the mantle can reach the surface via multiple ways, for example, carried by magma in the form of volcanic activities.”

It is possible that water is still being made this way deep inside Earth today, and the same could be true of other planets. The new simulation results are quite surprising “because rather than hydrogen bonding into the quartz crystal structure, it disrupts the structure completely by bonding with oxygen and forming water-rich regions below the surface”, says Lydia Hallis at the University of Glasgow, UK. “The study highlights how the minerals that make up Earth’s mantle can incorporate large amounts of water, and how Earth is probably ‘wet’ in some sense all the way down to its core.”

But despite the potential for the process to have created much of Earth’s water, Ludden thinks it may be small-scale and localised in comparison with the input of water from water-rich comets, meteorites and asteroids. “I think it’s reasonable to assume that much of the water came in this way,” he says.

Journal reference: Earth and Planetary Science Letters, DOI: 10.1016/j.epsl.2016.12.031

Articles originally appeared on New Scientist and  Science Daily

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