Tag Archives: mantle

The Nile is 30 million years old — and held together by movements in the Earth’s mantle

The River Nile over Cairo, Egypt. Image credits: Fakharany / Wikipedia.

It’s harder to imagine a more imposing river than the Nile. Stretching over 6,650 km (4130 miles) long and serving as an essential water source since time immemorial, the Nile is a lifeline across northern Africa. Ancient Egyptians considered the Nile river to be the source of all life, and believed the river to be eternal.

Recent research seemed to back that idea up — well, maybe the Nile wasn’t eternal, but it was around for a few million years — which is eternal by humanity’s standards.

The Nile has a surprisingly steady path, nourishing the valleys of Africa for millions of years and shaping the course of civilizations. But for geologists, that was weird.

Why is the Nile so steady when rivers (particularly larger rivers in flat areas) tend to meander so much?

Now, researchers at the University of Texas at Austin believed they’ve cracked that mystery, and it has a lot to do with movement inside the Earth’s mantle.

“One of the big questions about the Nile is when it originated and why it has persisted for so long,” said lead author Claudio Faccenna, a professor at the UT Jackson School of Geosciences. “Our solution is actually quite exciting.”

Convection belts in the mantle.

The team traced the geologic history of the Nile, correlating it with information from volcanic rocks and sedimentary deposits under the Nile Delta. They also carried out computer simulations that recreated tectonic activity in the area over the past 40 million years.

They linked the Nile’s behavior to a mantle conveyor belt.

“We propose that the drainage of one of the longest rivers on Earth, the Nile, is indeed controlled by topography related to mantle dynamics (that is, dynamic topography).”

The Earth’s interior is dominated by the mantle, and the mantle is not static. Large swaths of the mantle are moved around by convection. Sometimes, parts of that are pushed towards the surface. This upwelling magma has been pushing up the Ethiopian Highlands, helping to keep the river flowing straight to the north instead of wending its way sideways. This uplift, researchers conclude, is responsible for the gentle and steady gradient that keeps the Nile on a consistent course.

The Nile famously flows steadily to the North. Image credits: NASA.

Getting to this conclusion, however, was not straightforward — and it wouldn’t have been possible without state-of-the-art geophysical modeling. This proved to be the glue that pieced the entire theory together.

“I think this technique gives us something we didn’t have in the past,” said Jackson School scientists Petar Glisovic, one of the authors who is now a research collaborator at the University of Quebec.

As a consequence of this study, the researchers also showed that the Nile must be at least as old as the Ethiopian highlands — so this puts its age at 30 million years, which is several times more than previous estimates.

The study was published in Nature.

Deep diamonds hint at Earth’s primordial magma

A vast reservoir of magma lies undisturbed for billions of years. Researchers have seen signs of it in some superdeep diamonds.

Super-deep diamonds could help us learn more about unperturbed magma pockets. (Graham Pearson)

Our planet’s general structure is fairly simple: there’s a core, a mantle, and a crust. But the more you zoom in, the more complex things start to get. The crust, the thinnest layer of our planet, is immensely complicated and we’ve only managed to dig through to 13 km deep — with the average thickness of continental crust being around 35 km. The mantle is strongly influenced by convection currents. Some of it slowly creeps towards the surface, carrying heat and material from the planet’s interior to the surface — while in other places, the mantle absorbs portions of the crust. As for the core, almost everything we know about it comes from indirect information, and it’s remarkable that we know anything about it at all.

Not all the mantle might be engaged in such motion, however. Geologists have long suspected that there are pockets of magma that haven’t been moved in our planet’s constant churning.

The theory first came to life when researchers analyzed the ratio of two helium isotopes (helium 3 and helium 4) in some volcanic eruptions. The ratio was surprisingly similar to that of extremely old meteorites that crashed on Earth, hinting that the magma that flew in the volcanic eruptions was also extremely old.

“This pattern has been observed in ‘Ocean Island Basalts’, which are lavas coming to the surface from deep in the Earth, and form islands such as Hawaii and Iceland” said research leader Dr. Suzette Timmerman, from the Australian National University. “The problem is that although these basalts are brought to the surface, we only see a glimpse of their history. We don’t know much about the mantle where their melts came from”.

Diamonds, however, are extremely sturdy, and they can preserve inclusions much older than themselves.

Most diamonds form around 150-220 km below the planet’s surface, and are carried towards the surface. However, some diamonds can form up to 800 km deep, and these super-deep diamonds are quite different from normal ones. Timmerman explains:

“Diamonds are the hardest, most indestructible natural substance known, so they form a perfect time capsule that provides us a window into the deep Earth.”

“We were able to extract helium gas from twenty-three super-deep diamonds from the Juina area of Brazil. These showed the characteristic isotopic composition that we would expect from a very ancient reservoir, confirming that the gases are remnants of a time at or even before the Moon and Earth collided. From the geochemistry of the diamonds, we know that they formed in an area called the ‘transition zone’, which is between 410 and 660 km below the surface of the Earth. This means that this unseen reservoir, left over from the Earth’s beginnings, must be in this area or below it.”

Inclusions in microscopic cavities in the superdeep diamonds, like those shown in these electron microscope images, indicate the presence of primordial magma deep within the mantle. Image credits: Suzette Timmerman.

When the team analyzed the helium 3 to helium 4 ratio, they found the same ratio as in the old meteorites. Although the diamonds are “only” 500 million years old themselves, they were formed in a pocket of primordial magma, encapsulating some of the ancient helium 3 as it slowly diffused away.

This means that the diamonds were formed in such a pocket of unmoved magma, but we still don’t know where exactly this reservoir is and whether there is one big reservoir or multiple ones scattered across the globe. The composition of this reservoir is also unclear, but it is presumably quite dense, since it doesn’t seem to mix with the rest of the mantle, even after billions of years.

However, we now have confirmation that there is some material on Earth that has remained unmoved since the dawn of our planet, for some 4.5 billion years — and that’s pretty awesome.

The study has been published in Science.

Bermuda might hold the key to a whole new type of volcano

Researchers studying a volcano in Bermuda report that it is unlike anything else we’ve seen on Earth — it formed through a mechanism we knew nothing about until now.

About 30 million years ago, a disturbance in the mantle’s transition zone supplied the magma to form the now-dormant volcanic foundation on which Bermuda sits. Image credits: Wendy Kenigsberg/Clive Howard.

With its turquoise seas and pink beaches, Bermuda draws almost 1 million tourists every year. But far beneath the crystalline water, something draws a completely different crowd: scientists.

Cornell researchers had a hunch that there was something off about Bermuda’s volcanoes, so they analyzed a 2,600-foot (800-meter) core sample taken back in 1972. They were looking for isotopes, trace elements, evidence of water content, volatile materials — anything that would give some indication as to how the volcanoes were formed.

“I first suspected that Bermuda’s volcanic past was special as I sampled the core and noticed the diverse textures and mineralogy preserved in the different lava flows,” Mazza said. “We quickly confirmed extreme enrichments in trace element compositions. It was exciting going over our first results … the mysteries of Bermuda started to unfold.”

When the team analyzed the materials from the core, they found a clear signature of the “transition zone” — a layer rich in water, crystals and melted rock that lies beneath the outer and inner mantle. Before now, researchers didn’t know that volcanoes can form from the transition zone.

“We found a new way to make volcanoes. This is the first time we found a clear indication from the transition zone deep in the Earth’s mantle that volcanoes can form this way,” said senior author Esteban Gazel, associate professor in the Department of Earth and Atmospheric Sciences at Cornell University.

Cross-polarized microscopic slice of a core sample. Blue-yellow mineral is augite. Credits: Gazel lab.

Volcanoes were thought to form through one of two mechanisms: either when two tectonic plates subduct (one moves beneath the other), or when there is a deep mantle upwelling, as is the case in Hawaii. Surprisingly this wasn’t the case in Bermuda.

“We were expecting our data to show the volcano was a mantle plume formation — an upwelling from the deeper mantle — just like it is in Hawaii,” Gazel said. However, 30 million years ago, a disturbance in the transition zone caused the magma to flow towards the surface of what is now Bermuda.

Although geochemical studies of this type have been carried out in most volcanic parts of the world, Bermuda had escaped trialing until now. Now that they know what to look for, researchers say that there’s a good chance they might find these chemical signatures in other volcanic areas as well.

This suggests that the transition zone, which is located at a depth of 410-660 km (250 to 400 mi), is an important chemical reservoir for the Earth, bringing material from that depth and onto the surface.

The study has been published in Nature. DOI:10.1038/s41586-019-1183-6.

Globe.

There could be an extra, ancient layer of tectonic plates lurking under east Asia

A team of researchers from the University of Houston say they’ve possibly found a deeper body of tectonic plates floating within the mantle. These plates could explain a series of mysterious, very deep earthquakes in the Pacific ocean.

Globe.

 

While the theory of plate tectonics has been fought tooth and claw since its early days, it has gained widespread support in the last fifty or so years. The short of it is that the crust isn’t a single monolithic piece, but rather made up of a series of plates that bump into each other on an ocean of magma — the mantle. Continents piggyback on the plates, the ocean floor splits apart and spews magma where they drift apart, or sinks into the mantle to be recycled through subduction where the plates collide.

One underlying principle of plate tectonics is that of isostasy, which basically says that a) since these plates float on a fluid, their elevation depends on how dense they are and b) you can, in broad lines, delineate an area as being ‘the crust‘, since most plates will bob around this mean elevation and there’s no free magma on top, and ‘the mantle‘ which is underneath this crust.

The real sunken land

But on Tuesday, Jonny Wu from the University of Houston presented preliminary evidence at a joint conference of the Japan Geoscience Union and the American Geophysical Union in Tokyo that could blur the lines on point b) quite a lot.

Wu and his colleagues say that they’ve identified ancient tectonic plates which subducted in the mantle millions of years ago, but instead of being recycled they stabilized in the mantle’s transition zone (a water-rich layer at around 440-660 km depth). Beyond their choice of neighborhood, these sunken plates don’t differ that much from traditional plates in behavior. They slide horizontally at about the same speeds as surface plates, and can travel thousands of kilometers from the point of subduction. They can bend the same way surface plates do, and the energy released during a break can generate earthquakes — again, pretty typical plate mannerisms.

These plates could help explain the Vityaz earthquakes, a series of very deep, very powerful tremors whose hypocenters were, puzzlingly enough, traced in the mantle between Fiji and Australia. Wu and his team believe that the Vityaz earthquakes were caused by a subducted plate moving through the transition zone and hitting the sunken plate.

Sunken plate.

Seismic tomographic cross-section across NE Asia. Subducted plate in white/purple. Associated earthquakes
in red.
Image credits Jonny Wu et al., AGU Publications (2017).

Which is surprising, since subducted plates should theoretically sink right through the transition zone towards the core. But they explain that the plates subsiding under the western Pacific find themselves in a bit of a real-estate crisis.

“The Pacific subduction rate is so fast that you’ve got to find space to get all the slab in there,” Wu says, “and east Asia has had such a long history of subduction it’s jammed up. So this slab is forced to slide within the upper mantle and transition zone and be thrust under China.”

Why are we only hearing about this now?

Well first of all you have to remember that geophysics, the field of science which allowed this discovery is really really young. Some work pertaining to geophysics is older but the bread and butter of the field — sensors that can peer into the Earth and computers who can make sense of all the data — has been around for far less than the airplane. Plate tectonics wasn’t reliably proven until the 1960s when Hess advanced his ideas of sea floor spreading. That’s just 9 years before we put a man on the Moon.

So it’s very much a field still in progress. Wu’s discovery was made possible by recent technological advancements in seismological equipment, which allowed the team to model the mantle based on natural vibrations generated by earthquakes. Such snapshots into the Earth’s inner workings can be used to locate sunken plates still floating withing the mantle, and then reconstruct their likely shape and position on the planet’s surface millions of years ago.

“Think of Hubble. We look out, and the further we look out the more things we discover, not just about the universe – we’re actually looking back in time. And this new seismology is like turning the Hubble to look into the Earth, because as we look deeper and get clearer images, we can see what the Earth might have looked like further and further back in time.”

“We’re discovering lost oceans that we didn’t even know existed,” he added, referring to an 8,000km wide “East Asian Sea” his colleagues recently identified that likely spanned between the Pacific and Indian oceans 52 million years ago, and is now buried some 500 km to 1000 km deep in the mantle under east Asia.

Still, take these findings with a grain of salt. As exciting as they are, there are still a lot of questions left to answer and, as Wu himself points out, these are just preliminary findings and yet to undergo peer review. But if they do make it past the process, I’m sure we will be hearing a lot more about these sunken plates.

The preliminary paper “Philippine Sea and East Asian plate tectonics since 52 Ma constrained by new subducted slab reconstruction methods” has been published in the Journal of Geophysical Research Solid Earth.

Earth’s mantle is much hotter than we thought, scientists learn

We knew the Earth’s insides are hot, but just how hot are they? A new study found that the Earth’s mantle could go up to a whopping 1410 degrees Celsius (2570 degrees Fahrenheit), significantly more than was previously estimated.

Age of oceanic crust: youngest (red) is along spreading centres, where parts of the mantle rise up to create new crust. Credits: NOAA.

For once, something’s hotter and it’s not connected to global warming. The Earth’s mantle, the thickest layer of the Earth makes up 84% of the planet’s volume, lying between the Earth’s crust and its core. Because of its inaccessibility, pretty much everything we know about it comes from indirect evidence. Indeed, it’s a testament to how much geology has progressed that we’re able to describe it in such detail, but as it so often happens with indirect evidence, it can be quite difficult to get the figures exactly right. Now, this new study found that beneath our planet’s oceans, the mantle might be significantly hotter than we thought: by almost 110 degrees F (60 degrees C). This change could help us better understand tectonic processes and help us develop better models of our planet.

“Having such a hot mantle could mean that the mantle is less viscous (flows more easily), which could explain how tectonic plates are able to move on top of the asthenosphere,” the upper layer of Earth’s mantle, said study lead researcher Emily Sarafian, a doctoral student in the Geology and Geophysics Department at a joint program run by the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution.

Technically, the mantle is solid, but for geological purposes, it usually behaves like a fluid. Sounds strange? Well, imagine a jar of honey, which is viscous. The hotter it gets, the more liquid it becomes — and the opposite stands too, cold honey is quite solid.

“If you put honey in the fridge for an hour, it will barely flow when you take it out,” Sarafian said in an email to Live Science. “If, instead, you put honey on the stovetop, it will flow very easily, because it’s hotter.”

So the mantle is so hot that in some regards, it acts like a fluid. This is important because according to our understanding, there are convection currents in the mantle that move the tectonic plates around (and contribute to numerous geological processes). In other words, some parts of the mantle get hotter and become less dense, rising towards the surface. As they move, they transfer some of the heat towards the surface, where plumes of less dense magma break apart the plates at the spreading centers, creating divergent plate boundaries. At the other end of the process, some other end of tectonic plates cools down and sinks — thus, new crust is sometimes formed, and sometimes recycled in the mantle, maintaining an equilibrium.

Simplistic depiction of convection currents. Image credits: Wiki Commons.

To continue the analogy, imagine that the tectonic plates are like pieces of biscuit laid on top of the honey. If the honey (I mean, mantle) is hotter than we thought, then it means that it acts more like a liquid, and “flows more,” so to speak. It means that the currents might be stronger than we thought and the biscuits (plates) might “float” with less resistance — it also means that our current models might need some tweaking.

Hotter than hell

We knew very well that the mantle is hot, there’s plenty of clues to indicate that. For instance, it generates the hot lava that flows out from underwater volcanoes. We also know of the gravitational heat, left over from when gravity first condensed our planet from the hot gases and particles, and perhaps most significantly, of the heat from radioactive decay. But because we can’t really probe it directly, we’ve relied on models and lab experiments to estimate its temperature. The one piece of direct evidence we have is from mantle xenoliths — rocks that were brought up from the mantle by convection currents and exposed by mid-oceanic ridge spreading, but because those rocks undergo processes that significantly change their structure and chemistry, researchers prefer to create synthetic rocks to model conditions.

After the synthetic rock is created in the lab, researchers subject it to pressures and temperatures ranging around those of the mantle and see at what temperature it melts. This is called the solidus temperature. The problem with estimating this temperature is water. Due to a chemical quirk, water greatly affects the solidus temperature of these rocks. Therefore, estimating the water content of the rocks is essential for determining the solidus temperature.

Other teams were aware of this issue, “but they were never able to quantify how much water was in their experiments because the mineral grains that grow during an experimental run at mantle pressures and temperatures are way too small to measure with current analytical techniques,” Sarafian said. She added that researchers were using some corrections, adding a bit of extra water to the synthetic rock — but this correction was unnecessary, as the rocks already accumulate the water from the atmosphere.

She found the missing puzzle piece in olivine, a magnesium iron silicate with larger grains, which can be better measured. So she added olivine to the mix, which allowed her to measure water content more accurately.

A beautiful olivine crystal, not from this study. Image credits:
Rob Lavinsky

 

“We performed melting experiments the same way that previous scientists did, putting a synthetic rock to high pressure and temperatures, but by adding these grains to our experiments, we were giving ourselves a target that was large enough to analyze for water content,” she said.

With the new water correction, a different solidus temperature emerged, and a different temperature of the mantle.

Paul Asimow, a professor of geology and geochemistry at the California Institute of Technology who was not involved with the study, complemented the research in an accompanying commentary in the journal Science, saying that it is “an appreciable correction.”

Journal Reference: Emily SarafianGlenn A. GaetaniErik H. HauriAdam R. Sarafian — Experimental constraints on the damp peridotite solidus and oceanic mantle potential temperature. Science 03 Mar 2017: Vol. 355, Issue 6328, pp. 942-945.
DOI: 10.1126/science.aaj2165

 

Huge, rare diamonds help us learn more about the Earth’s mantle

Geologists analyzing diamonds of exceptional size and quality have uncovered new clues about the Earth’s geology. By analyzing their chemistry and structure, researchers were able to infer things about the Earth’s mantle, an area inaccessible to direct research.

Diamonds can be used in jewelry… or they can help us better understand the planet’s geology. Image credits: Jennifer Dickert

Diamonds, despite being really expensive, are not entirely that rare. In fact, they’re routinely used in several industrial branches. But big diamonds on the other hand, that’s a completely different story – they’re not only much rarer, but also significantly different. Large gem diamonds like the Cullinan have a unique set of physical characteristics.

“Some of the world’s largest and most valuable diamonds, like the Cullinan or Lesotho Promise, exhibit a distinct set of physical characteristics that have led many to regard them as separate from other, more common diamonds. However, exactly how these diamonds form and what they tell us about the Earth has remained a mystery until now,” explains Dr. Wuyi Wang, GIA’s director of research and development, and an author of the study.

Some of these diamonds grow to such sizes because they were formed in the depths of the Earth, at 360-750 km below the surface (approximately 224-466 miles), in the convecting mantle – much lower than most diamonds which generally form at 150-200 km (approximately 93-124 miles). Being formed at these depths, some of them carry within chemical inclusions from that part of the mantle  – a solidified mixture of iron, nickel, carbon and sulfur, with some traces of fluid methane and hydrogen in the thin tiny space between the metallic phases and the encasing diamond. As diamonds grow, small droplets of metallic liquid were occasionally trapped within. In other words, they encase within them a part of the deep mantle’s chemistry, providing us with a direct example of something we would normally just infer.

“This new understanding of these large, type IIa diamonds resolves one of the major enigmas in the study of diamond formation — how the world’s largest and most valuable diamonds formed,” says Smith. “The composition of the inclusions, however, provides the story.”

Of course, sampling the biggest (and most expensive) diamonds in the world is hardly possible. But big diamonds are always polished and some parts (the scratchings) are not that interesting for jewelers. Normally, these scratchings would also be unavailable, but Smith and his team were lucky enough to be given permission for study. What they want to see now is whether this chemical distribution is localized, or is found everywhere throughout the mantle.

“Previous experiments and theory predicted for many years that parts of the deep mantle below about 250 km depth contain small amounts of metallic iron and have limited available oxygen. Now, the metallic inclusions and their surrounding methane and hydrogen jackets in these diamonds provide consistent, systematic physical evidence to support this prediction,” explains Smith.

Journal Reference: E. M. Smith, S. B. Shirey, F. Nestola, E. S. Bullock, J. Wang, S. H. Richardson, W. Wang. Large gem diamonds from metallic liquid in Earths deep mantle. Science, 2016; 354 (6318): 1403 DOI: 10.1126/science.aal1303

Inclusion

Evidence of water 1,000 kilometers under the surface found locked inside a diamond

Analysis of a mineral inclusion in a 90-million-years-old diamond revealed that the Earth’s mantle might hide a lot more water than we believed, buried as deep as 1,000 kilometers below the surface.

Inclusion

Image credits Mederic Palot.

Water one-third of the way to the Earth’s core – it’s a revolutionary idea. But it’s one that a diamond, spewed out by a volcano near the São Luíz river in Juina, Brazil, some 90 million years ago, seems to point at. The discovery came from analysis of a sealed inclusion, an imperfection in the stone, which contains minerals trapped by the forming diamond.

Through infrared microscopy, scientists analyzing the material found it included hydroxyl ions in its chemical make-up, a compound usually formed from water molecules. And there were a lot of these ions present in the inclusion. But just finding out there was water around where the diamond was one thing – the team also had to determine the depth at which this happened. Once again, they turned their eyes to the inclusion.

They found it was mainly composed of ferropericlase, a mixture of iron and magnesium oxide which can absorb some other metals, such as chromium, aluminum, and titanium, in the extremely hot and pressurized environment of the lower mantle. Jacobsen found that these “extra” metals had separated from the ferropericlase, a phenomena that can only take place in milder conditions as the diamond inches towards the surface. Based on the composition, they estimate the inclusion formed at around 1,000 kilometers deep. The inclusion was sealed in the diamond since the beginning, and for the metals to be present at all, it had to have originated in the lower mantle. That means the water signature can only come from the lower mantle.

“This is the deepest evidence for water recycling on the planet,” he says. “The big take-home message is that the water cycle on Earth is bigger than we ever thought, extending into the deep mantle.”

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

The findings could support the theory that the Earth had always had water, instead of having it shuttled in by comets and other space rocks.

The full story appeared in print, New Scientists issue 3101, under the headline “Oceans of water in deep Earth go 1000 km down.

 

Kola gate to hell, sealed, 2006

Drilling to the Mantle: 6 unexpected discoveries from the world’s deepest well

Today – December 16, 2015 – a drilling rig on a ship has parked above a spot in the Indian Ocean. Here they will begin drilling toward the mantle. The scientists work for the International Ocean Discovery Program. They plan to bore through six kilometres of tough oceanic basalt – the Earth’s crust – and then pierce the mantle. No one has ever drilled into the mantle before, but there have been a half dozen serious attempts.

Kola well's derrick: world's deepest well, around 1980 (Credit: Wikipedia)

                                Kola well’s derrick in 1980: still the world’s deepest hole (Credit: Wikipedia)

 

Decades ago, the Russians drilled deeper than anyone has ever gone. Their Kola Superdeep Borehole was started in 1970 and still holds the world record for the deepest hole in the ground. But they didn’t reach the mantle. As the latest mantle drilling project begins today off the coast of Africa, people are wondering if a billion dollars for the newest hole in the ground is worth the money. We can’t say. We don’t know what the team in the Indian Ocean might learn. But back in the ’70s and ’80s, no one expected the results the Soviets got from their 12,262-metre-deep borehole.

Here are 6 unexpected discoveries from the world’s deepest well:

  1. There’s a lot of water down there. Hot mineralized water was found almost everywhere along the drill path. Everyone figured that the granite would be as dry as a stone. Who says you can’t get water from a rock?
  2. To cut miles into the ground, the engineers had to invent a whole new drill. In the past, drillers quickly spun the entire drillstem so the bit at the bottom could chew the bedrock. Before starting, the Soviets calculated that the tubing would weigh over a million pounds. They could never generate enough torque to rotate that much pipe fast enough to drill through kilometres of granite. So, in 1969, the Soviets invented a rotary bit. It spun by sending pressurized mud down the pipe where it blew through a turbine at the drill head, spinning it 80 revolutions per minute. It worked and the system is now used on oil wells.
  3. The Earth has gas. Unexpectedly, helium, hydrogen, nitrogen, and even carbon dioxide (from microbes) were found all along the borehole.
  4. There is no basalt under the continent’s granite. This was a huge surprise. Seismic suggested that at 9,000 metres the granite would give way to basalt. It doesn’t. The seismic anomaly that suggested basalt was caused by metamorphosed granite instead. This gave support for plate tectonics, which was a new theory when the Kola Superdeep Borehole was being drilled.
  5. There are fossils in granite 6,700 metres below the surface. How’d that happen?
  6. Hell is deeper than 12,262 metres. There’s a persistent rumour that the drilling ended in 1992 because scientists pierced a super-hot cavity and heard the screams of damned souls. Not likely. For that, they probably needed to actually reach the mantle.

Kola gate to hell, sealed, 2006

                                       Door to Hell: the Kola well head was sealed in 2006.  (Credit: Rakot13)

 

.

earth mantle layer

Scientists discover another layer in the Earth’s mantle

Most people tend to think of the Earth in terms of crust, mantle and core, and while those are indeed the largest “layers” (you can’t properly call the mantle a layer though), each one of them is made from other, thinner layers. Now, researchers from the University of Utah have identified another one of these thinner layers, 930 miles beneath our feet.

earth mantle layer

An illustration of a slab of rock sinking through the upper mantle above, through the boundary between the upper and lower mantle at 410 miles depth, then stalling and pooling at a depth of 930 miles. Image credits: University of Utah.

“The Earth has many layers, like an onion,” study co-author Dr. Lowell Miyagi, an assistant professor of geology and geophysics at the University of Utah, said in a written statement. “Most layers are defined by the minerals that are present. Essentially, we have discovered a new layer in the Earth. This layer isn’t defined by the minerals present, but by the strength of these minerals.”

Their finding actually has some significant implications. Geophysicists had previously observed that many slabs that are otherwise active and “move around” inside the Earth get stuck at around 930 miles underground – a phenomenon thought to lead to seismic activity and increased volcanic activity. This layer seems to be the cause.

“The result was exciting,” Miyagi said in the statement. “In fact, previous seismic images show that many slabs appear to ‘pool’ around 930 miles, including under Indonesia and South America’s Pacific coast. This observation has puzzled seismologists for quite some time, but in the last year, there is new consensus from seismologists that most slabs pool.”

Miyagi holding a press that houses the diamond anvil, in which minerals can be squeezed at pressures akin to those deep within the Earth.

Oceanic plates are denser and when they collide with continental plates, they typically subduct, triggering earthquakes and volcanism. The subduction process takes place at very long times even geologically, with some estimates putting a 300 million years time stamp for a full subduction. Miyagi and fellow mineral physicist Hauke Marquardt, of Germany’s University of Bayreuth wanted to see why some slabs dive all the way through the mantle, and some stop. This is important because when they stop, they “bump”, potentially creating a deep earthquake.

“Anything that would cause resistance to a slab could potentially cause it to buckle or break higher in the slab, causing a deep earthquake,” Miyagi said.

They used a device a diamond anvil to simulate how the mineral ferropericlase reacts to high pressure – they squeezed thousands of crystals of ferropericlase at pressures up to 960,000 atmospheres. They focused specifically on ferropericlase, a magnesium/iron oxide virtually inexistent on the surface, but one of the main constituents of the lower mantle. They found that the stiffness (or viscosity) of the mineral increased threefold by the time it was subjected to pressure equal to what’s found in the lower mantle (930 miles below Earth’s surface) compared to the pressure at the boundary of the upper and lower mantle (410 miles beneath the surface). The results were quite surprising because it was thought that viscosity varies only slightly in the depths of the mantle.

Miyagi says the stiff upper part of the lower mantle also may explain different magmas seen at two different kinds of seafloor volcanoes and may mean that the lower mantle is hotter than previously believed.

 

The Thickest Layer of the Earth

The Earth can be divided into four main layers: the solid crust on the outside, the mantle, the outer core and the inner core. Out of them, the mantle is the thickest layer, while the crust is the thinnest layer.

The Earth’s structure

Artistic depiction of the Earth's structure. Image via Victoria Museum.

Artistic depiction of the Earth’s structure. Image via Victoria Museum.

The Earth’s structure can be defined in several ways, but general, we see the Earth as having a solid crust on the outside, an inner and an outer core, and the mantle in between. The crust’s thickness varies between some 10 km and just over 70 km, having an average of about 40 km. The core has, in total, a radius of 3500 km, but it is generally viewed as two distinct parts:

  • the solid inner core, with a radius of 1220 km
  • the viscous outer core, with a radius of 2300 km

The mantle’s thickness is about 2900 km – so if you consider the Earth’s core as one big thing, then the core is the “thickest layer” (though has a bigger radius is probably a better way of saying it) – but the idea of a separate outer and inner core is generally accepted.

The Mantle – thickness and composition

The mantle comprises about 83% of the Earth’s volume. It is divided into several layers, based on different seismological characteristics (as a matter of fact, much of what we know about the mantle comes from seismological information – more on that later in the article). The upper mantle extends from where the crust ends to about 670 km. Even though this area is regarded as viscous, you can also consider it as formed from rock – a rock called peridotite to be more precise. A peridotite is a dense, coarse-grained igneous rock, consisting mostly of olivine and pyroxene, two minerals only found in igneous rocks.

Peridotite, as seen on the Earth’s surface. Image via Pittsburgh University.

But it gets even more complicated. The crust is divided into tectonics plates, and those tectonic plates are actually thicker than the crust itself, encompassing the top part of the mantle. The crust and that top part of the mantle (going 00 to 200 kilometers below surface, is called the asthenosphere. Scientific studies suggest that this layer has physical properties that are different from the rest of the upper mantle. Namely, the rocks in this part of the mantle are more rigid and brittle because of cooler temperatures and lower pressures.

Below that, there is the lower mantle – ranging from 670 to 2900 kilometers below the Earth’s surface. This is the area with the highest temperatures and biggest pressures, reaching all the way to the outer core.

Mantle Trivia: Even though you can consider the mantle as molten rock or magma, modern research found that the mantle has between 1 and 3 times more water than all the oceans on Earth combined.

How can we study the mantle?

Waves propagating from Earthquakes through the Earth. Image via Brisith Geological Survey.

Waves propagating from Earthquakes through the Earth. Image via Brisith Geological Survey.

Pretty much all the practical geology we do takes places at the crust. All the rock analysis, the drilling… everything we do is done in the crust. The deepest drill ever is some 12 km below the surface… so then how can we know the mantle?

As I said earlier, most of what we know about the mantle comes from seismological studies. When big earthquakes take place, the waves propagate throughout the Earth, carrying with them information from the layers they pass through – including the mantle. Furthermore, modern simulations in the lab showed how minerals likely behave at those temperatures and pressures, and we also have indirect gravitational and magnetic information, as well as studies on magma and crystals found on the surface. But the bulk of the information comes from seismic analysis.

Image via Wiki Commons.

Seismic waves, just like light waves, reflect, refract and diffract when they meet a boundary – that’s how we know where the crust ends and where the mantle begins, and the same goes for the mantle and the core. The waves also behave differently depending on different properties, such as density and temperature.

In the mantle, temperatures range between 500 to 900 °C (932 to 1,652 °F) at the upper boundary with the crust; to over 4,000 °C (7,230 °F) at the boundary with the core. Thanks to the huge temperatures and pressures within the mantle, the rocks within undergo slow, viscous like transformations  there is a convective material circulation in the mantle. How material flows towards the surface (because it is hotter, and therefore less dense) while cooler material goes down. Many believe that this convection actually is the main driver behind plate tectonics.

Mantle convection may be the main driver behind plate tectonics. Image via University of Sydney.

Another interesting fact about the mantle: Earthquakes at the surface are a result of stick-slip faulting; rocks in the mantle can’t fault though, yet they sometimes generate similar earthquakes. It’s not clear why this happens, but several mechanisms have been proposed, including dehydration, thermal runaway, and mineral phase change. This is just a reminder of how little we still know about our planet: we’ve only scratched the surface of the thinnest layer, the crust.

Earth may have generated its own water – geologically

A new study may have finally found where Earth’s water came from. There are currently two competing theories, with one claiming that our planet generated its own water geologically, while the other suggests that water was brought by icy comets or asteroids from outside. A new study concluded that most of the water we see today likely comes from the Earth’s mantle.

Water beneath the surface

Image via Special Papers.

Until recently, the idea that water came to Earth from somewhere else in the solar system seemed to have more support, but studies conducted by the European Space Agency on the Rosetta missions showed that water almost certainly didn’t come from comets. Wendy Panero, associate professor of earth sciences at Ohio State, and doctoral student Jeff Pigott believe that when the Earth formed, it had huge bodies of water in its interior, and has been continuously supplying water to the surface via plate tectonics, circulating material upward from the mantle.

Researchers have long known that there is some water in the earth’s mantle, but nobody knows just how much. Because you can’t go 40 km deep and study the mantle, you have to rely on indirect information and computer simulations.

“When we look into the origins of water on Earth, what we’re really asking is, why are we so different than all the other planets?” Panero said. “In this solar system, Earth is unique because we have liquid water on the surface. We’re also the only planet with active plate tectonics. Maybe this water in the mantle is key to plate tectonics, and that’s part of what makes Earth habitable.”

The thing is, when we’re talking about water in the mantle, it’s not actually liquid water – what seems dry to the human eye may actually have significant quantities of water – in the form of hydrogen and oxygen waters. Hydrogen is typically stored in crystal voids and defects, while oxygen is usually plentiful in most minerals. Certain reactions can free up the hydrogen and oxygen, resulting in water; but could it be enough water to amount for the oceans we see today?

The key element here is ringwoodite.

High-Pressure Olivine

Olivine is a magnesium-iron silicate typically found in the mantle and igneous rocks. However, in the mantle, at very high pressures and temperatures, the olivine structure is no longer stable. Below depths of about 410 km (250 mi) olivine undergoes a transformation, transforming into ringwoodite or bridgmanite. Ringwoodite is notable for being able to contain hydroxide ions (oxygen and hydrogen atoms bound together) and previous research has already shown that the earth’s mantle holds huge quantities of water.

Now, this team has found that the mineral bridgmanite doesn’t contain enough water to play a significant role in this issue – so it’s all about the ringwoodite. But the question is – if ringwoodite is trapped in the mantle and the water is drained towards the surface in plate tectonics, how does our planet still have water reserves now, in the mantle?

But while they were creating some models and simulations of ringwoodite water behavior, another likely candidate emerged: garnet. Garnet could be a water carrier, transporting some of the water to the surface, while some of it still remains in the mantle.

“If all of the Earth’s water is on the surface, that gives us one interpretation of the water cycle, where we can think of water cycling from oceans into the atmosphere and into the groundwater over millions of years,” she said. “But if mantle circulation is also part of the water cycle, the total cycle time for our planet’s water has to be billions of years.”

 

 

Earth’s most abundant mineral finally gets a name

What’s the most common mineral on Earth? Is it quartz, limestone? Maybe olivine? Well, if you take into consideration the entire planet, the most common mineral would be something known as silicate-perovskite – but now, that mineral finally has a name.

A sample of the 4.5 billion-year-old Tenham meteorite that contains submicrometer-sized crystals of bridgmanite. Yes, it’s that really small thing.

On June 2, bridgmanite was approved as the formal name for silicate-perovskite – possibly of the Earth’s most plentiful yet elusive mineral known to exist in the Earth’s lower mantle, between 670 and 2,900 kilometers (416 and1,802 miles). . The name was given in honor of 1946 Nobel Prize winning physicist Percy Bridgman, honoring his researches concerning the effects of high pressures on materials and their thermodynamic behaviour.

You won’t find any bridgmanite on the surface, as the mineral naturally exists only in the lower part of the mantle (which is made 93% from it). Scientists have known (or had very strong theories regarding its existence) for decades, but were unable to find a surface sample, until this year.

“This [find] fills a vexing gap in the taxonomy of minerals,” Oliver Tschauner, an associate research professor at the University of Nevada-Las Vegas who characterized the mineral, said in an email.

Tschauner worked with his colleague, Chi Ma, a senior scientist and mineralogist at the California Institute of Technology in Pasadena, Calif., to characterize the structure of silicate-perovskite since 2009. However, this year they made a big breakthrough, after analyzing a meteorite which fell in Australia in 1879. The meteorite formed 4.5 billion years ago, and was “highly shocked”.

“Shocked meteorites are the only accessible source of natural specimens of minerals that we know to be rock-forming in the transition zone of the Earth,” said Tschauner.

After throughly analyzing it with every available technique, they were finally able to find the bridgmanite veins in the meteorite. Thus, confirming decades of research, they were also able to submit an official name for the mineral, which they did in March 2014.

“We are glad no one used [Bridgman] for other minerals,” said Ma, “this one is so important.”

First ringwoodite sample confirms huge quantities of water in the Earth’s mantle

The first ever terrestrial discovery of ringwoodite seems to confirm the existence of massive amounts of water hundreds of kilometers below the Earth’s surface. Let me explain how.

Under pressure

Ringwoodite is a high-pressure polymorph of olivine; it’s basically olivine, but with a different crystal structure. The mineral is thought to exist in large quantities in the so-called transition zone, 410km to 660 km deep. Judging by its properties and lab experiments, crystallographers believe that the mineral is restricted between 525 and 660 km deep.

Ringwoodite has been found in meteorites, but until now, no terrestrial sample has ever been unearthed because, well, geologists can’t go 500 km deep underground. However, a University of Alberta diamond scientist has found the first terrestrial sample. The team led by Graham Pearson, Canada Excellence Research Chair in Arctic Resources analyzed this ringwoodite sample and reported that it contains a significant amount of water – 1.5 per cent of its weight. Since this mineral is thought to be found in enormous quantities in the transition zone, that means that the equivalent of all the surface water is found inside the minerals.

“This sample really provides extremely strong confirmation that there are local wet spots deep in the Earth in this area,” said Pearson, a professor in the Faculty of Science, whose findings were published March 13 in Nature. “That particular zone in the Earth, the transition zone, might have as much water as all the world’s oceans put together.”

Interestingly enough, the mineral is notable for being able to contain water within its structure, present not as a liquid but as hydroxide ions (oxygen and hydrogen atoms bound together) . This has huge implications because ringwoodite is thought to be the most abundant mineral phase in the lower part of Earth’s transition zone, so abundant that its properties directly affect those of the mantle – so the existence of water is quite a game changer.

The sample that almost wasn’t

Pearson holding the sample. Remember that the ringwoodite inclusion is a very small part of the sample.

The sample was found in 2008 in the Juina area of Mato Grosso, Brazil, where artisan miners unearthed the host diamond from shallow river gravels. Diamonds are most often associated and brought to the surface by minerals called kimberlites – the most deeply derived of all volcanic rocks. But the discovery itself was almost accidental.

Pearson’s team was looking for something entirely different when they stumbled onto a three-millimetre-wide, dirty-looking, commercially worthless brown diamond. The ringwoodite itself is invisible to the naked eye, and hidden beneath the surface, so it’s a surprise that graduate student, John McNeill, found it in 2009.

“It’s so small, this inclusion, it’s extremely difficult to find, never mind work on,” Pearson said, “so it was a bit of a piece of luck, this discovery, as are many scientific discoveries.”

Three-dimensional confocal μXRF view of two-phase inclusion within the diamond

It took years of analysis and redoing the tests over and over again before it was finally confirmed that the sample is ringwoodite; infrared spectroscopy and X-ray diffraction confirmed this, while the critical water measurements were performed at Pearson’s Arctic Resources Geochemistry Laboratory at the U of A.

A remarkable collaboration

Aside from actually finding the sample, it’s also notable how this study came to fruition. It is a remarkable example of ome of the top leaders from various fields, including the Geoscience Institute at Goethe University, University of Padova, Durham University, University of Vienna, Trigon GeoServices and Ghent University. For Pearson, one of the world’s leading authorities in the study of deep Earth diamond host rocks, this is one of the most notable discoveries in his career, apparently confirming 50 years of theories.

Geophysicists and seismologists have long theoretized that the composition of the transition zone has to feature immense quantities of water, but that was never confirmed – until now. The existence of water in the ringwoodite in the transition zone has immense implications for volcanism and plate tectonics, affecting how rock melts, cools and shifts below the crust.

“One of the reasons the Earth is such a dynamic planet is the presence of some water in its interior,” Pearson concluded. “Water changes everything about the way a planet works.”

Journal Reference:

  1. D. G. Pearson, F. E. Brenker, F. Nestola, J. McNeill, L. Nasdala, M. T. Hutchison, S. Matveev, K. Mather, G. Silversmit, S. Schmitz, B. Vekemans, L. Vincze.Hydrous mantle transition zone indicated by ringwoodite included within diamondNature, 2014; 507 (7491): 221 DOI: 10.1038/nature13080

Geophysicists find a layer of liquefied rock in the Earth’s mantle that acts as a lubricant for tectonic plates

Scientists at Scripps Institution of Oceanography at UC San Diego have found a layer of liquefied molten rock in Earth’s mantle that may be acting as a lubricant for the sliding motions of the planet’s tectonic plates. This discovery has very far reaching implications, which can solve some of the long standing geological puzzles, as well as lead to a better understanding of earthquakes and volcanism.

Electromagnetic measurements

plate tectonics1

They used a relatively common, but uniquely improved geophysical technique (magnetotellurics), which involved advanced seafloor electromagnetic imaging technology. They imaged a 25-kilometer- (15.5-mile-) thick layer of partially melted mantle rock below the edge of the Cocos plate where it moves underneath Central America. They basically deployed a vast array of seafloor sensors that monitor the natural electromagnetic signals to map features of the crust and mantle. Back in 2010, they started noticing something was weird – they were finding magma in unexpected places.

cocos plate 2

“This was completely unexpected,” said Key, an associate research geophysicist in the Cecil H. and Ida M. Green Institute of Geophysics and Planetary Physics at Scripps. “We went out looking to get an idea of how fluids are interacting with plate subduction, but we discovered a melt layer we weren’t expecting to find at all-it was pretty surprising.”

cocos plate

The marine electromagnetic technology employed in the study was originated by Charles “Chip” Cox, an emeritus professor of oceanography at Scripps, and further improved by Constable and Key. The method has been so successful, that since 2000, they have been working with big oil companies to map out offshore oil and gas reservoirs.

The planetary engine

Plate tectonics is, if you will, the backbone of modern geology and geophysics. It is not perfect, by any standards, but it is a good theory that describes the large-scale motions of Earth’s lithosphere; one thing that’s been puzzling is the exact forces and mechanisms that allow the planet’s tectonic plates to slide across the earth’s mantle; one theory was that as minerals go deeper in the mantle, the water they contain is ejected, and this results in a more ductile mantle that would facilitate tectonic plate motions. However, no clear data has been provided to confirm or infirm this theory.

“Our data tell us that water can’t accommodate the features we are seeing,” said Naif, a Scripps graduate student and lead author of the paper. “The information from the new images confirms the idea that there needs to be some amount of melt in the upper mantle and that’s really what’s creating this ductile behavior for plates to slide.”

Indeed, if there isn’t some major flaw with this study, then it could pretty much change the way we view this sliding mechanism.

tectonics lubricant

The orange area inside the dashed lines is the lubricant layer which facilitates the plate motion. The blue areas represents the Cocos plate subducting beneath the central American continent, and the black points are the earthquakes.

“This new image greatly enhances our understanding of the role that fluids, both seawater and deep subsurface melts, play in controlling tectonic and volcanic processes,” said Bil Haq, program director in the National Science Foundation’s Division of Ocean Sciences.

To get to the conclusion that there is a layer which acts as a lubricant, they studied the fluid content of the subducting plate offshore Nicaragua and Costa Rica. Magnetotellurics and controlled source electromagnetics imaged the porosity variations associated with lithospheric bending and cracking near the trench, as was suggested by a previous reflection seismic imaging. Analyzing the obtained parameters, they modeled this lubricant layer.

Their results, if valid, could help geologists better understand the genesis of some earthquakes, as well as some questions unanswered for decades.

“One of the longer-term implications of our results is that we are going to understand more about the plate boundary, which could lead to a better understanding of earthquakes,” said Key.

Now, the next step is to figure out how exactly is this layer formed and the source that supplies this magma.

Via Scripps Research Institute

Understanding magma in the mantle: rocks melt at greater depth than previously thought

Magma forms much deeper than geologists previously believed, according to a new study conducted by Rice University.

Magma and Crust

 

mantle

The group led by geologist Rajdeep Dasgupta put very small samples of peridotite under very large pressures, to find out if the rock can liquify, at least in small amounts, as deep as 250 km beneath the ocean floor. Peridotite is the dominant rock of the Earth’s mantle above a depth of about 400 km, and it was previously believed that the mineral doesn’t liquify above that depth.

mantle structure

The Rice team focused on mantle beneath oceans because that is where the crust is typically formed; in a much-simplified version, the silicate melts (magma) rise with the convective currents, cool as they reach the crust and then solidify to create new crust. The starting point for melting has long been thought to be at 70 kilometres beneath the seafloor.

 

Geophysics

 

In order to determine the mantle’s density and properties, geophysicists used seismic information; seismic waves from earthquakes travel the globe much like sound waves, and by measuring their speed, we can estimate some the medium’s properties. These waves travel faster in solids (especially in denser solids), and slower in liquids; the first questions arose here.

Seismologists have observed anomalies in their velocity data as deep as 200 kilometers beneath the ocean floor,” Dasgupta said. “Based on our work, we show that trace amounts of magma are generated at this depth, which would potentially explain that.”

seismic wave

So it didn’t really add up – and this wasn’t the only clue. Geophysicists have also struggled to explain the bulk electrical conductivity of the oceanic mantle – something which was observed but couldn’t really be figured out.

“The magma at such depths has a high enough amount of dissolved carbon dioxide that its conductivity is very high,” Dasgupta said. “As a consequence, we can explain the conductivity of the mantle, which we knew was very high but always struggled to explain.”

The thing is, we cannot really dig down to the mantle – this is miles away from happening, both figuratively and literally, so we have to rely on indirect measurements (seismology, electric measurements, etc), lab experiments and surface extrapolations. Another interesting they found in this experiment was that carbonated rocks melt at significantly lower temperatures than non-carbonated.

“This deep melting makes the silicate differentiation of the planet much more efficient than previously thought,” Dasgupta said. “Not only that, this deep magma is the main agent to bring all the key ingredients for life — water and carbon — to the surface of the Earth.”

Volcanic windows

However, Dasgupta believes that volcanic rocks are the key to understanding our planet’s mantle.

“Our field of research is called experimental petrology,” he said. “We have all the necessary tools to simulate very high pressures (up to nearly 750,000 pounds per square inch for these experiments) and temperatures. We can subject small amounts of rock samples to these conditions and see what happens.”

A surfaced volcanic rock - peridotite

A surfaced volcanic rock – peridotite

To subject the rocks to these hellish conditions, they use massive hydraulic presses.

“When rocks come from deep in the mantle to shallower depths, they cross a certain boundary called the solidus, where rocks begin to undergo partial melting and produce magmas,” Dasgupta said. “Scientists knew the effect of a trace amount of carbon dioxide or water would be to lower this boundary, but our new estimation made it 150-180 kilometers deeper from the known depth of 70 kilometers,” he said.

These findings have major implications for all planetary sciences:

“What we are now saying is that with just a trace of carbon dioxide in the mantle, melting can begin as deep as around 200 kilometers. And when we incorporate the effect of trace water, the magma generation depth becomes at least 250 kilometers. This does not generate a large amount, but we show the extent of magma generation is larger than previously thought and, as a consequence, it has the capacity to affect geophysical and geochemical properties of the planet as a whole.”

The paper will be published this week in Nature

Chikyu sets a new world drilling-depth of scientific ocean drilling

The Japanese scientific deep sea vessel Chikyu managed to set a new world record by drilling down to over 2.200 meters below the seafloor, obtaining samples from Shimokita Peninsula of Japan in the northwest Pacific Ocean.

Drilling for science

Whenever you hear about drilling, it’s almost always about oil. Given the humongous amount of oil we use nowadays, it makes sense there are over 3.000.000 active oil rigs in the world – just mind blowing! Still, scientific drilling, despite neglected by comparison, has some remarkable accomplishments.

Typically, scientific drilling is used for recovering probes, samples of sediments, crust, and even upper mantle in extreme cases. Researchers are also able to study, in some cases, microbial life preserved in the samples. Especially recently, scientific drilling is going through a revolution, and its results are constantly improving in recent years, Chikyu being a clear example of that; until now, sea drilling was used without a a riser. Riser-less drilling uses seawater as its primary drilling fluid, which is pumped down through the drill pipe, cleaning and cooling the drill bits, piling them in a cone around the hole. However, Chikyu uses a riser, and the whole technology, although more complicated, also becomes more efficient, as you can see in the picture above.

A new era for scientific drilling

Chikyu – dawning a new era in scientific drilling

Chikyu made this achievement during the Deep Coalbed Biosphere expedition, Expedition 337, conducted as part of an international effort, the Integrated Ocean Drilling Program (IODP).

“We have just opened a window to the new era of scientific ocean drilling”, Fumio Inagaki, Co-Chief scientist of Expedition 337, says. “The extended record is just a beginning for the Chikyu. This scientific vessel has tremendous potentials to explore very deep realms that humans have never studied before. The deep samples are precious, and I am confident that our challenges will extend our systematic understanding of nature of life and earth.”

His European colleagues are just as thrilled:

“I am very glad that I am here today and could witness this wonderful and important moment. Everybody on the ship worked really hard to make this happen. And, I am very pleased about the high quality of the core samples, which show only minimal drilling disturbance. This is very important for our research.”, added Co-Chief scientist Kai-Uwe Hinrichs from the University of Bremen, Germany.

Samples retrieved featured mostly deeply buried coal – its formation was the main purpose of the expedition, and researchers hope it will be able to provide new insight regarding how deep life is associated with a hydrocarbon system in a deep marine subsurface.

Part of Earth’s mantle is shown to be conductive under high pressures and temperatures

Ever since researchers started studying the Earth’s spin, they noticed that the spin isn’t perfect. Many believe this is a result of the different elements in the Earth’s core, mantle and crust, which have different densities and generate different friction.

Most researchers studying this wobble agreed that the mantle would have to respond to the magnetic tug of the core – but the problem here is that the mantle is made out of rocks, and not only metals, like the core, and therefore shouldn’t be conductive; hence, quite a predicament. However, new research done by Kenji Ohta and his colleagues at Osaka University in Japan.

As they describe in their paper published in Physical Review Letters, it appears that a mineral called Wustite (FeO), believed to be a significant component of the Earth’s mantle, can be made to conduct electricity at high temperatures and pressures.

In order to test their theory, they raised the mineral up to 1600°C and applying 70 gigapascals of pressure, and they found it becomes just as conductive as an average metal. To find out what happens in even harsher conditions, they heated the mineral to 2200°C and doubled the pressure – finding the same results, suggesting that the same thing would happen even deeper in the mantle, closer to the core-mantle boundary.

In order to better understand why this particular mixture of Oxygen and iron becomes conductive at high pressures, the team did density and electrical conductivity tests and their results seem to suggest that this metallization is related to the spin crossover.

Dinosaur extinction ocean of lava

New dinosaur extinction theory: an ocean of lava

Dinosaur extinction ocean of lava

It wasn’t just a devastating asteroid that killed off all the dinosaurs 65 million years ago. Scientists from Boston University now claim that a massive eruption of lava fronts around the world, coinciding with the asteroid impact, sealed their fate forever.

The controversial theory is betting on two unusually hot blobs of mantle 1,700 miles beneath the crust that formed just after Earth itself, 4.5 billion years ago. These mantle stores are responsible for huge amounts of lava gush from the bowels of the Earth, flooding more than 100,000 square kilometres, leaving behind distinct geological regions known as large igneous provinces (LIPs).

Matthew Jackson at Boston University and his team found 62-million-year-old basalts from the North Atlantic LIP contain isotopes of elements in ratios that reflect the chemistry of early Earth’s mantle. The scientists claim that this is hard evidence supporting the supposed fact that LIPs are fed by the 4.5-billion-year-old stores of mantle.

“There is an amazing correlation between mass extinctions and LIPs,” Andrew Kerr at the University of Cardiff says.

These ancient magma stores might actually be still active to this day. Using seismic waves to probe the mantle’s structure, scientists found two unusual areas some 2800 kilometres down, beneath Africa and the Pacific Ocean.

It’s an interesting idea – that a giant blob of hot magma might burp from near Earth’s core every now and then, causing havoc for life,” says Gerta Keller at Princeton University, but adds more work is needed to support the hypothesis.

The researchers themselves also admit that they can perfectly understand why this theory can be considered highly controversial, however they believe it’s still highly plausible.

 

Melt rises up 25 times faster than previously believed

lava_lake_night

Scientists have for the first time determined the actual permeability of the asthenosphere in Earth’s upper mantle, which is basically responsible for how fast the melt rises towards the surface of the earth, and the results were surprising to say the least. Researchers found that it actually moves 25 times faster than previously assumed, which forces us to reconsider every volcanic model that includes melt.

A huge centrifuge measuring 2 meters in diameter was embedded in the cellar’s floor. It spins at 2800 rotations per minute and creates an acceleration about 3000 times bigger than Earth’s gravity; when at full capacity, it creates 120 decibels, which is about as loud as an airplane, according to Max Schmidt, a professor from the Institute for Mineralogy and Petrology at ETH Zurich. It can reach 850 km/h, and after it reaches this speed, if you would turn it off, it takes about an hour to stop.

This globally unique centrifuge cast a whole new light on how we perceive magmatism. The researchers used it to simulate the transport of molten lava made of basaltic glass from the mid-ocean ridge. The matrix through which the melt passed through consisted of olivine, which makes about 2/3 of the upper mantle. They applied a temperature of 1300 degrees and a pressure of 1 giga pascal. After the basaltic mass melted, they accelerated to about 700 g’s and were then able to calculate the permeability directly by microscopic analysis and were then able to correlate porosity to permeability, which is a main part for thermo-mecanical models.

In the light of these new discoveries, these models have to be revised; if the magma ascends much faster that means it interacts a lot less with the rock it penetrates. It also explains a few things, such as why volcanoes are active for only a few thousand years.