Skip to main content

Does dark magma lurk in deep Earth?






A key to understanding Earth's evolution is to look deep into the lower mantle—a region some 400 to 1,800 miles (660 to 2,900 kilometers) below the surface, just above the core. Data have suggested that deep, hot, fluid magma oceans of melted silicates, a major Earth material, may reside above the core-mantle boundary. Researchers including Carnegie's Alex Goncharov have found, using high-pressure experiments with a proxy material, that the deep Earth materials conduct far less heat under increasing pressure than previously thought. The finding suggests that pressure is more important than current thinking and it is in direct contrast to what is found with the most abundant heat-conducting substance in the vicinity. The results indicate the presence of dense, dark magma heat traps that could affect the flow of heat across the core-mantle boundary revealing a different model of heat transport in this region.

The research is published in the November 11, 2014 issue of Nature Communications.
Since scientists can't sample the Earth's deep interior, they study how seismic waves travel through the Earth to determine whether material is solid, liquid, or has other features. The detection of anomalous low-wave velocities suggests that dense, gravitationally bound melted silicate exists at the core-mantle boundary. However, direct measurements of the ability of this material to carry heat have not been technically possible. The research team studied two forms of silicate glass, an analogous material, under pressures up to 840,000 times atmospheric pressure, mimicking conditions of the core-mantle boundary.
Heat transfer occurs at a higher rate across materials of high  than across materials of low thermal conductivity. To observe how materials conduct heat, scientists manipulate materials while monitoring their physical properties. For example, under certain conditions minerals transmit light. Researchers can measure changes in transmission through the material induced by increased pressure, which affects the electronic structure and consequently thermal transport properties.
The team, led by Motohiko Murakami of Tohoku University (Sendai, Japan), measured the visible and near-infrared  of two types of  subjected to enormous pressure generated between two diamond tips in an anvil cell. The method allowed the scientists to detect tiny changes in the energy levels of the iron-enriched silicate glasses as it underwent pressure increases. The findings were further supported using a technique called Mössbauer spectroscopy, which showed changes in electronic configuration of iron ions that correlated with the observed increase in optical absorption.
"We were totally surprised to find that the radiative thermal conductivity decreases with pressure for both glasses," remarked Goncharov. "This result is in contrast to what is observed with the other major constituent of the lower mantle, perovskite. The heat transfer rate for the glass is about 5-25 times less than that of silicate perovskite—such a difference would strongly affect the flow of heat at the core-mantle boundary. It suggests the formation of deep, dark magmas with higher heat absorption than the surrounding material. This means it could trap  from the underlying core and could lead to large-scale thermal upwellings called superplumes."
He continued: "To gain a greater understanding of what is happening in this region, scientists need to come up with novel techniques for in situ measurements of thermal transport properties under simultaneous conditions of high pressure and high temperatures in fluid silicates. These experiments are currently extremely challenging, but they should become possible with the developments of new pulsed-laser techniques coupled to laser-heated diamond anvil cells, which are currently underway in our Carnegie lab. Our goal is to look at the real melted silicate at very high temperatures, which in principle could reveal different properties than the glasses we looked at."
Labels:

Comments

Post a Comment

Popular posts from this blog

This strange mineral grows on dead bodies and turns them blue

If you were to get up close and personal with Ötzi the Iceman – the 5,000-year-old mummy of a  tattooed ,  deep-voiced  man who died and was frozen in the Alps – you’d notice that his skin is flecked with tiny bits of blue. At first, it would appear that these oddly bluish crystal formations embedded in his skin are from freezing to death or some other sort of trauma, but it’s actually a mineral called  vivianite  (or blue ironstone) and it happens to form quite often on corpses left in iron-rich environments. For Ötzi, the patches of vivianite are  from him resting  near rocks with flecks of iron in them, but other cases are way more severe. According to Chris Drudge at Atlas Obscura , a man named John White was buried in a cast iron coffin back in 1861. During those days, coffins often had a window for grieving family members to peer inside even if the lid was closed during the funeral. Sometime after he was buried, that window broke, allowing groundwater to come inside the
Post a Comment
Read more

It's Official: Time Crystals Are a New State of Matter, and Now We Can Create Them

Peer-review has spoken. Earlier this year , physicists had put together a blueprint for how to make and measure time crystals - a bizarre state of matter with an atomic structure that repeats not just in space, but in time, allowing them to maintain constant oscillation without energy. Two separate research teams managed to create what looked an awful lot like time crystals  back in January,  and now both experiments have successfully passed peer-review for the first time, putting the 'impossible' phenomenon squarely in the realm of reality. "We've taken these theoretical ideas that we've been poking around for the last couple of years and actually built it in the laboratory,"  says one of the researchers , Andrew Potter from Texas University at Austin. "Hopefully, this is just the first example of these, with many more to come." Time crystals  are one of the coolest things physics has dished up in recent months, because they point to a
Post a Comment
Read more

The Dark Side Of The Love Hormone Oxytocin

New research shows oxytocin isn't the anti-anxiety drug we thought it was. Oxytocin, the feel-good bonding hormone released by physical contact with another person, orgasm and childbirth (potentially encouraging  monogamy ), might have a darker side. The  love drug  also plays an important role in intensifying  negative emotional memories  and increasing feelings of fear in future stressful situations, according to a new study. Two experiments performed with mice found that the hormone activates a signaling molecule called extracellular-signal-related kinases (ERK), which has been associated with the way the brain  forms memories   of fear . According to Jelena Radulovic, senior author on the study and a professor at Northwestern University's medical school, ERK stimulates fear pathways in the brain's lateral septum, the region with the highest levels of oxytocin. Mice without oxytocin receptors and mice with even more oxytocin receptors than usual were placed in
Post a Comment
Read more