Tag Archives: tectonics

A tectonic plate off the coast of Portugal might be peeling off

Geologists believe we may be witnessing the birth of a new subduction zone.

Image via Wikipedia.

Researchers have long puzzled over a plain, featureless area off the coast of Portugal. The seemingly-boring area stood out in 1969 when it triggered a massive earthquake that generated a tsunami. This was highly unusual — earthquakes don’t just happen in random areas. Most often, they take place in tectonically active areas, at the edges of tectonic plates. The correlation is so good that if you’d look at a global map of large earthquakes (see below), it looks like a map of tectonic plates.

So why then did a 7.9 earthquake shake the coast of Portugal? João Duarte, a marine geologist from the Instituto Dom Luiz at the University of Lisbon, believes he has the answer. According to a recent study published by Duarte, the tectonic plate off Portugal’s coast might be peeling away from its top.

Actively tectonic

The Earth might seem static from our point of view, but from a geological perspective, it’s very active. Our planet’s crust is split into rigid plates which are always in motion to each other, at a rate of a few centimeters per year — which, in millions of years, can dramatically change the surface of the Earth.

Earthquakes happen most commonly on the edge of tectonic plates. Image via Wikipedia

Naturally, when the plates are moving, they will sometimes be pushing against each other. If one plate is heavier than the other, it will slide beneath it — a process called subduction. We’re quite familiar with subduction as we’ve observed it and its effects in several parts of the world, but we’ve never actually seen it start. Until now.

Suspicions of a potential subduction-related peeling event started after the 1969 earthquake, but it wasn’t until 2012 that researchers got a good view of the area, using seismic wave analysis (which works somewhat similar to an ultrasound). In 2018, Chiara Civiero, a postdoctoral researcher at University of Lisbon’s Instituto Dom Luiz, and her colleagues published a high-resolution peek into Earth in this region, and confirmed the discovery of the unusual blob.

Now, Duarte found new evidence to support this theory in a seemingly innocuous geological layer, one which allows water to percolate (infiltrate) through. This water transforms the minerals inside the plate, transforming them into softer minerals, producing just enough weakness to allow the bottom of the plate to peel away.

“Now we are 100-percent sure it’s there,” Duarte told Nationl Geographic. Other researchers found that above this deep body, which stretches 155 miles below the surface, tiny quakes seemed to tremble.

Of course, work is still needed to confirm the find, but Duarte is confident.

“It’s a big statement,” Duarte says of the conclusions, acknowledging that he and his team still have work to do. “Maybe this is not the solution to all the problems. But I think we have something new here.”

The study was presented at the European Geosciences Union meeting.
Europa TectPun.

Europa’s tectonics might be powered by salt, could sustain life on the moon

New research suggests that Europa’s icy shell may exhibit tectonic systems similar to those on Earth. This would have major implications for live developing on the moon.

Europa TectPun.

Image credits Alex Micu / ZME Science; free to use with attribution.

A team of Brown University researchers used computer modeling to show that subduction — the “sinking” of tectonic plates — is physically possible on Jupiter’s freezing moon, Europa. The result support earlier work that identified regions on the moon’s ice shell which seem to be expanding in a fashion similar to what we see down here on Earth. Overall, the study fleshes our understanding of tectonic processes in general, those on Europa in particular, and raises some very exciting possibilities regarding life in its undersurface waters.

Tectonics on the rocks

“What we show is that under reasonable assumptions for conditions on Europa, subduction could be happening there as well, which is really exciting,” says Brandon Johnson, assistant professor in Brown’s Department of Earth, Environmental and Planetary Sciences and a lead author of the study.

We’ve found several different types of tectonic systems in the solar system, from Venus’ hickey-like coronae to Mercury’s contraction-powered tectonics. Back down on our own plastic-laden corner of the Universe, subduction is powered chiefly by differences in temperature. The crust, Earth’s outer layer, is formed of plates floating on top of the mantle (an ocean of fluid, molten rock). Being solid and cold, these plates are denser than the material in the mantle — this bulk provides the negative buoyancy that pulls crustal slabs into the mantle.

A few years ago, Europa was also shown to maintain its own tectonic processes. Despite having an icy, rather than rocky, crust, there was evidence that processes very similar to Earth’s subduction were going on. But we didn’t have any idea why. We have reason to believe that the moon’s interior is kept warm by the gravitational tug of its massive host, Jupiter. This means that Europa’s ice shell is made up of two layers, Johnson says — a thin outer cover of very cold ice sitting atop a slightly warmer, convecting layer. So the working hypothesis was that surface slabs would break off and sink through the mushy ice below.

Europa poster.

The layers of Europa.
Image credits Kelvinsong / Wikimedia.

There is one major hiccup with that hypothesis, however: as the slabs pushed down into the warmer ice below, they would quickly warm to match its temperature. When that happened, the slab would have the same density of the surrounding ice — so they wouldn’t sink.

Johnson and his team developed a subduction model that could be maintained across Europa regardless of these temperature differences. What they used is salt. A difference in salinity between the two ice layers would provide the density gap needed for a slab to subduct.

“Adding salt to an ice slab would be like adding little weights to it because salt is denser than ice,” he explains. “So rather than temperature, we show that differences in the salt content of the ice could enable subduction to happen on Europa.”

Evidence in support of a salinity difference in Europa’s layers come from the moon’s occasional water upwellings — a process similar to magma upwellings here on Earth. Such events leave behind salty traces on the crust.

Sink 4 life

Plumes Europa.

Composite image shows a suspected plume of material erupting two years apart from the same location on Europa.
Image credits NASA/ESA/W. Sparks (STScI)/USGS Astrogeology Science Center.

The results help patch up our understanding of Europa’s tectonics and help us get a better understanding of how Earth’s tectonic processes work. It also bolsters the case for a habitable(-ish, at least) ocean on the moon by pointing to an undersurface ocean that’s dynamic enough to sustain tectonics.

Perhaps most excitedly, it teases with the possibility of organisms eeking out a living below the frozen surface.

“If indeed there’s life in that ocean, subduction offers a way to supply the nutrients it would need,” Johnson adds.

So what do tectonic processes have to do with life? Well, life (as we understand it) needs a lot of different building blocks including hydrogen, oxygen, nitrogen, phosphorous, and sulfur. These are usually found in ample supply in planets, but they’re not evenly spread around. Even worse, life consumes these basic nutrients wherever it happens to pop up.

Tectonics brings a lot of matter motility to the scene. By churning everything while sinking and moving about, tectonic plates make sure elements are recirculated vertically throughout a planetary system, ensuring there’s always something tasty for organisms to munch on when new plates form.

It’s by no means a “there’s life on Europa, you guys” find, but some important conditions are there. Which makes NASA’s upcoming mission to Europa just that much more exciting.

The paper “Porosity and salt content determine if subduction can occur in Europa’s ice shell” has been published in the Journal of Geophysical Research: Planets.

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.

Venus does tectonics without any plates — and it’s possible young Earth did it too

Venus might be tectonically active, a new paper reveals — but it’s not the plate tectonics we know and love from back home.

Computer-generated synthetic aperture radar mosaics of Venus from the first cycle of Magellan mapping.
Image credits NASA / JPL.

It’s so similar to Earth that it’s often called its twin, and yet, Venus seems to lack one of the defining features of Earth: tectonic plates. This has been bugging planetary scientists for a long time now because our pearly neighbor should be an ideal host for such processes — but they insist on popping up on Mercury or Europa — a moon out of all places — and pointedly absenteeing from Venus.

So why is Venus such a good candidate for plate tectonics? Well, it’s really similar to the Earth as far as size and chemical composition are concerned. Its surface is also littered with volcanoes. We don’t know for sure which are active or not — the surface is hidden behind thick clouds that make repeated observations nigh impossible — but at least they’re proof that there once was a lively geology in the mantle. The proverbial coffin nail is that Venus is pockmarked by craters and material accumulated over hundreds of millions of years or successive eruptions. So tectonic recycling clearly doesn’t take place here.

Men come from Mars, evidence of tectonics comes from Venus

But it may be the case that Venus just has its own flavor of tectonics. For instance, there are some features on Venus, such as trenches and rifts, that point to some kind of tectonic activity. Under normal circumstances, researchers would try to digitally model internal processes and progressively tweak them until the model matched what we see on the surface — but, according to the team of French and US researchers behind the paper, the models currently at our disposal simply aren’t powerful enough to handle a 3D model of Venus’ mantle and crustal activity in enough detail.

Instead, they used an old-fashioned physical model to figure out what was happening. The team used a solution of silica nanoparticles (i.e. finely ground sand) in suspension in water to match the physical properties of semi-solid rock. Put over a heating plate, this medium re-created the convection cells generated in Venus’ mantle as hot (and thus less dense) material pushes up from the planet core towards the crust.

The team used cameras to monitor the evolution of their model. Over time, as water evaporated, a thin crust started to form on top of the container. On this crust, something similar to distinctive features of Venus’ crust (formations called coronae) began forming on the simulated crust. These “volcano-tectonic features unique to Venus” are circular structures which can grow to a few thousand kilometers across, with a mound-like rise in the center. The rise is predominantly made up of igneous rocks, while the edge is bumpy and ends with a deep trench. This trench is very similar to what happens in the areas where tectonic plates get subducted back on Earth, although the rest of the corona isn’t.

Experiment picture.

Side views of the model. Plume shown in red, effect on surface in yellow, subduction zones in white. Blue arrows show the movement of rocks.
Image credits A. Davaille et al., (2017), Nature.

The team believes that a phenomenon underlying plate tectonics on Earth also creates Venus’ coronae: mantle plumes. Think of them like really big convection cells, with the upwelling material burning through the crust like a blowtorch. On Earth, mantle plumes are responsible for hotspots of volcanic activity especially for volcanoes that are smack-dab in the middle of plates, like Yellowstone or Iceland, and those stringy volcanic island arcs like Hawaii. Sometimes, they can be powerful enough to burn through whole tectonic plates and break them apart.

But that happens because Earth’s crust is pretty thick and solid. Venus is a much hotter place, with average surface temperatures revolving around 450 degrees C (840 F), making its crust thinner and more flexible — so mantle plumes have a different effect. As the team’s model showed, when a plume hits the crust, molten rock is pushed up fractures and faults to the surface. This added weight causes the crust to sag, widening the fractures, making more material pile on, and so forth. Eventually, the whole section of the crust will rupture, sink, and melt into the mantle.

Artemis corona.

The Artemis corona is actually made up of 5 different coronae. a) Combined radar (greyscale) and topography (color scale) image; corona-like features labeled ‘c’. Rift segments radiating out from the trench labeled ‘r’. b) Terrain shape along the B-B′ line. c) Radar image showing a 200-km-wide area with graben-like lineation, on average 300 km in length and 1 km in width, spaced at 6-12 km.
Image credits A. Davaille et al., (2017), Nature.

This unique take on tectonics is what we see as a corona. The central igneous bit is deposited by material pushed up by the plume, surrounded by a circular equivalent of a subduction trench. The authors compare their model’s result to two important coronae, Artemis and Quetzalpetlatl, and find that the features observed in the lab line up pretty well to those seen on Venus.

Venus’ coronae might hold an unexpected glimpse into the Earth’s past, too. The team notes that temperature conditions on Venus today are very similar to what Earth had for much of its early history. So it’s possible that there was a more Venus-like tectonic system in place down here before the Earth cooled down enough for plate tectonics to take a hold.

The full paper “Experimental and observational evidence for plume-induced subduction on Venus” has been published in the journal Nature Geosciences.

 

Mercury will join the Solar System’s “tectonically active” planet club

Mercury becomes the second confirmed tectonically active planet in the Solar System, as new evidence from the MESSENGER spacecraft finds developing fault lines on the scorching planet.

For a long time, Earth was believed to be the only planet in our Solar System which could boast tectonic activity. This geologic liveliness has been linked to our planet’s unique ability to sustain life — but now, NASA found evidence of similar activity on Mercury. The MESSENGER spacecraft swooped in close to the tiny planet on its last 18 months orbiting it and found evidence of shifting pieces of crust and developing fault lines.

The photographs suggest that Mercury is still contracting, joining Earth as a tectonically active planet in the Solar System.

Image credits Watters et al., 2016, Nature Geoscience.

“The young age of the small scarps means that Mercury joins Earth as a tectonically active planet, with new faults likely forming today as Mercury’s interior continues to cool and the planet contracts,” said lead researcher Tom Watters, Smithsonian senior scientist at the National Air and Space Museum in Washington, DC.

Mercury isn’t the first body in the system or the only other planet apart from Earth to show these signs — we’re also suspecting similar activity on Europa, Jupiter’s watery moon, and UCLA professor of Earth and space sciences An Yin is building a strong case for tectonic activity on Mars. It hasn’t yet been confirmed, but scientists suspect that Jupiter’s tidal lock on the planet is what keeps its subsurface warm enough to stay liquid, in essence powering its tectonics. Yin’s paper is still awaiting peer-review.

However, with an 88-day orbit around the Sun, no atmosphere, and temperatures skyrocketing from -173 degrees Celsius (–280 degrees Fahrenheit) at night to a scorching 427 degrees Celsius (800 degrees Fahrenheit) during the day, Mercury sadly remains decidedly uninhabitable.

Researchers hope that by better understanding this activity on this tiny world, we’ll more easily spot similar processes on worlds outside of the Solar System. They’ll keep studying the planet’s magnetic field and surface activity to gain insight into the inner workings of the planet.

“This is why we explore,” said Jim Green, NASA’s planetary science director. “For years, scientists believed that Mercury’s tectonic activity was in the distant past. It’s exciting to consider that this small planet – not much larger than Earth’s moon – is active even today.”

The findings, titled “Recent tectonic activity on Mercury revealed by small thrust fault scarps” have been published in Nature Geoscience.

What is Gondwana: the supercontinent

Gondwana used to be a supercontinent, from around 550 million years ago to approximately 180 million years ago, alongside Laurasia. Gondwana incorporated present-day South America, Africa, Arabia, Madagascar, India, Australia, and Antarctica.

The Earth is a planet alive.

That shouldn’t surprise anyone — after all, our planet is bustling with life on the surface. But it goes deeper than that, literally. The atmosphere, the magnetic field that prevents solar radiation from frying us alive, the terrain on which we live — these are all the product of lively processes taking place under the surface.

For most people, the world around us seems like a very stable place. Its shape seems, pardon the pun, set in stone. But the continents we know today are only a temporary arrangement, and they looked very different in Earth’s earlier history.

Be patient enough, and you’ll see the earth itself spring to life — it moves, breaking apart or coming together all over the planet. This is the story of the last in a breed of geological titans, a supercontinent we named Gondwana.

A different Earth

Some 500 million years ago, during the late Ediacaran period, tectonic motions brought today’s Africa, South America, Australia, Antarctica, India, the Arabian Peninsula and Madagascar into a single, massive piece of land. This was the early version Gondwana, stretching from the Equator almost to the south pole. Its climate was mild, however, as the world was a warmer place back then. Multicellular organisms had developed by this time, but they were primitive. The few fossils we’ve found from this period show a biota consisting of segmented worms, round creatures resembling modern jellyfish, and frond-like organisms.

More continents collided with this early Gondwana over time to form Pangaea, the “whole Earth,” roughly 300 million years ago. It was immense by any stretch of the imagination, all of the planet’s landmass was fused into one block dominating the southern hemisphere, surrounded by the biggest ocean in history. Then, 20 to 70 million years later, magma plumes from the Earth’s core started burning through the crust like a blowtorch, creating a rift between what we know today as Africa, South America, and North America.

Pangea’s breaking-up stages.
Image credits U.S. Geological Service.

Convection cells associated with these plumes widened the fissure into a fully fledged Tethys ocean, separating a northern supercontinent called Laurasia — today’s North America, Europe, and Asia — from a southern one, our fully formed Gondwana. It has lost some of its original bits to Laurasia — such as Florida and parts of Georgia — but still contains all the landmasses we see today in the southern hemisphere. We’re now in the Jurassic period. Dinosaurs are roaming about, most of the world is covered in lush rainforests, and the last supercontinents are poised to break up.

It’s not you, it’s tectonics

The break-up didn’t happen at once, however. Gondwana fragmented in stages. Sometime between 170 million and 180 million years ago, modern Africa and South America began breaking apart from the rest of Gondwana. They stayed fused for about 30 to 40 million years until the South Atlantic Rift broke them up, opening the ocean (with the same name) between them.

That’s why South America’s eastern coast and Africa’s western coast look like they’d fit together snugly — at one point, they actually did.

South America and Africa with the approximate location of their Mesoproterozoic (older than 1.3 Ga) cratons (old and stable parts of the crust.)
Image credits Woudloper / Wikimedia.

At about the same time as the South Atlantic Rift was opening up, the easternmost part of the continent, Madagascar and India, split from the rest, opening the central Indian Ocean. The two stayed fused together until the Late Cretaceous period, after which India made a beeline for Eurasia —  50 million years ago, the collision between the two was so violent it raised the Himalayas.

At this point basically all that’s left of former Gondwana is Australia and Antarctica — too little to be counted as a supercontinent. They did stay fused together until around 45 million years ago, though. After that, Antarctica moved south and froze over (due to a combination of the climate cooling down and shifting ocean currents around the new landmasses) and Australia went adrift towards the north, colliding with southern Asia. The collision is still taking place today, as the Australian plate is advancing north at a rate of about 3 centimeters (1.2 inches) a year.

Today’s tectonic plates. Red arrows indicate primary direction of movement.
Image credits U.S. Geological Survey.

We still don’t know exactly what caused the continent to break apart. One theory holds that hot spots formed beneath it, creating rifts that broke the supercontinent apart. In 2008, however, University of London researchers suggested that Gondwana instead split into two tectonic plates, which then were then further fragmented.

How we figured all of this out

The uncanny resemblance between the shape of western Africa and eastern South America was first officially noted by Sir Francis Bacon in 1620 as accurate maps of the two continents became available. In 1912, Alfred Wegener, a German meteorologist, proposed that the two continents formed a single body at one point — in fact, he was the first to envision the great supercontinent Pangaea. However, geologists at the time strongly criticised his theory, citing his lack of formal training in the field. Geologists then couldn’t believe that something as huge as a continent could move; they simply lacked knowledge of a system that would explain how this could happen; they had no known way to reliably recreate the movements.

Alexander Du Toit, a South African geologist, further elaborated on the theory in his 1937 book Our Wandering Continents. Seeing the opposition Wegener’s theory encountered, he carefully amassed evidence of the two continents’ past link — the occurrence of glacial deposits (or tillites) and rock strata on both sides of the Atlantic, as well as similar fossil flora and fauna found exclusively on southern continents, especially the fern species Glossopteris. His theory gained traction with scientists from the southern hemisphere but was still widely criticised by geologists in the northern hemisphere. They envisioned land bridges spanning from continent to continent to explain how one species could be found on both sides of an ocean, even to the point where these bridges would circle whole continents.

However, the theory of plate tectonics became widely embraced by the 1960s when the Vine–Matthews–Morley hypothesis was formed following paleomagnetism (or fossil magnetism) measurements of the ocean’s floor. These measurements recorded the magnetic properties stored in ocean-bottom rocks as they formed over time, proving that rift areas add new material to oceanic plates, pushing continents apart.

This cemented the theory of tectonic plates, and furthermore helped us understand how these imense landmasses moved in the past — including how Gondwana came to be and ultimately broke up.

How magnetic stripes form on the sea floor.
Image credits Chmee2 / Wikimedia.

Gone-dwana

Gondwana is the last of the supercontinents the world has seen — so far. Plates are being formed and consumed today, just as they have been since the Earth’s crust cooled down to a solid. The same tectonic processes that made and shattered Gondwana and the supercontinents before it functions just the same, powered by the huge quantity of heat trapped in the depths of the Earth. They will keep on mashing continents together, so it’s almost guaranteed that a new supercontinent will form in the future.

But considering the timeframes geology works with, we’re probably not going to be around any longer to see it happen.

 

You can now travel in time and see how Earth’s geology changed

How did South America slot next to Africa? Where was my country a billion years ago? Thanks to a cloud-based virtual globe developed by University of Sydney geologists, anyone with access to internet can now find out the answer to those questions and many others.

This is a reconstruction of the supercontinent Pangea 180 million years ago. The colors correspond to fluctuations in the continental gravity field, which reflect the deep continental structure such as roots of ancient mountain chains, basins and fold belts. These features are used to solve the puzzle of re-arranging all continents from today¹s positions to their ancient placement in Pangea.

[The interactive globes can be viewed on any browser at: portal.gplates.org]

Reported today in PLOS ONE, the globes have been gradually made available since September 2014. Some show the Earth as it is today, while others draw from geological reconstructions to depict how it was like millions, hundreds of millions, and even a billion years ago. To my knowledge, this is the first and only interactive portal which allows this. You can see the supercontinents moving around, putting a pleasant image on tricky concepts from tectonics.

“Concepts like continental drift, first hypothesised by Alfred Wegener more than a century ago, are now easily accessible to students and researchers around the world,” said University of Sydney Professor of Geophysics Dietmar Müller.

“The portal is being used in high schools to visualise features of the Earth and explain how it has evolved through time.”

The portal doesn’t only highlight the planet’s geology and continental or tectonic plates’ positions. You can also visualize seabed geology, a global digital elevation model as well as the global gravity and magnetic field. Visualizing the plates moving towards/away from each other and reacting to the huge pressure is enthralling.

“When continents move over hot, buoyant swells of the mantle they bob up occasionally causing mountains,” said Professor Müller. “Conversely the Earth’s surface gets drawn down when approaching sinking huge masses of old, cold tectonic slabs sinking in the mantle, creating lowlands and depressions in the earth’s crust.”

The project has been highly successful and as mentioned above, is already being used in an educational context in several highschools. However, open-access big data offers everyone and anyone the possibility to take advantage of centuries of research.

“These cloud-based globes offer many future opportunities for providing on-the-fly big data analytics, transforming the way big data can be visualised and analysed by end users,” said Professor Müller.

The seafloor geology globe is the most popular one, viewed on average 500 times per day.

 

 

Volcanic twins of the Red Sea: Sholan and Jadid

We tend to think of the planets as static, enduring, and never changing. With the average human life spanning only decades, we can be forgiven that the dimension of time in which geological processes take place goes a bit over our heads. However, recent images captured by satellites showing the birth of two volcanic islands published in a study by Nature Communications are a powerful reminder that the Earth is a planet alive under its crust as well as above.

We’re gonna need a bigger diaper.
Image via arstechnica.com

The two islands, named Sholan and Jadid formed during volcanic eruptions in the Zubair archipelago in 2011 and 2013, respectively. They provided an excellent opportunity for scientists to study a rare and not fully understood phenomenon: the creation of land by submarine eruptions. Only a few such eruptions have been witnessed since the emergence of Surtsey Island to the south of Iceland in the 1960s.

Using high-resolution optical satellite images, the study charts the rapid growth of the new islands during their initial eruptive phases and how their shape changes as the waves wash over their coasts: they are being eroded fast by the waters of the Red Sea, one of the islands losing over 30% of its surface in just two years.

The southern part of the Red Sea is a new ocean-to-be, forming as tectonic plates spread apart at about 6mm per year. Under its waters a range of mountains created by volcanic eruptions, an embryonic mid-ocean ridge, forms at the point where these two plates’ boundaries are closest. The structure spreads following the system that feeds the eruptions, magma-filled cracks called dykes.

Tectonic spreading, with magma rising to the surface and mid-ocean ridge formation.
Image via www.divediscover.whoi.edu

Seismic activity similar to that recorded during the islands’ formation has also been recorded in the past, but without emersion of new land. Scientists suggest that this is caused by underwater eruptions or the formation of new intrusive structures in the crust (such as dykes), suggesting that this area is more volcanically active than previously thought.

Looking at the satellite captured images and data pertaining to ground deformation geologists discovered that while the islands measure in at about 1-km in diameter the dykes are at least 10-km in length. This is similar to other areas where spreading takes place, such as Iceland, where geological activity becomes focused around a few vents as the eruption progresses, supporting their claim that active tectonic spreading is taking place in the area.

Sholan and Jadid’s creation has provided scientists with valuable insight into geological processes, but perhaps more importantly, their birth reminds us that the ground underneath our feet was born, lives and one day will return to the earth. It’s alive. Just like us.

 

Beaked whale reveals Africa’s tectonic secrets

Some 17 million years ago, a beaked whale took a wrong turn up an African river, something which ultimately turned out to be its demise. But now, geologists studying the whale’s fossils believe the whale’s unfortunate end might shed a new light on early human evolution, putting a timestamp on when the environment started to change in East Africa, enabling humans to evolve.

Magady lake at the bottom of caldera (old chimney) Ngorongoro. Tanzania, east-African plateau. Julia A. Kalinkina, October, 2006

The Cradle of Humanity

17 million years ago, we’re in the Neogene, in a period called the Burdigalian; back then, Africa looked entirely different, with the East African Plateau being substantially lower and covered by rich, dense forests. Because it was so low lying and close to the ocean, there was enough water to go around and the forest was properly nourished. But as the plateau started to rise, the land started to dry up, and East Africa slowly turned into the savannah we see today.

Geologists have wondered for quite a while when that uplift actually happened, especially because those areas of eastern Africa are the cradle of humanity – where our species developed and slowly started to walk on two feet. It was this uplift that caused the climate to change, that in turn caused the vegetation and environment to shift, ultimately allowing us to develop as a species. This whale fossil is actually very important, because it tells a part of the story.

“The whale is telling us all kinds of things,” said study co-author Louis Jacobs, a paleontologist at Southern Methodist University in Dallas. “It tells us the starting point for all that uplift that changed the climate that led to humans. It’s amazing.”

“It’s more or less the story about the bipedalism,” said study researcher Henry Wichura, a postdoctoral candidate in geoscience at University of Potsdam in Germany.

Pictured: James G. Mead excavating the whale specimen in the “Open Pit Turtle Mine”, Williams’ Flat Loperot, Kenya, Summer 1964. (Photo : James G. Mead)

The fossil was actually found 50 years ago, in 1964, but a study on it wasn’t published until 1975. Then, they misplaced the skull until 2011. Jacobs read the 1975 paper and had been looking for this skull since the 1980s, when he was head of paleontology at the National Museums of Kenya. Every time Jacobs visited Harvard, Washington or Nairobi, he would try to find it and study it, but every time he came back empty handed.

“It was protected by a plaster jacket, so you couldn’t really see it,” he said. “I suspect nobody knew what it was. It was just kept in the collections there.”

Ultimately, in 2011, he managed to locate it and remove the plaster coating. He then contacted Wichura, who is a structural geologist studying the uplift of the East African plateau and found that rivers and lava had flowed east from high points on the plateau at least 13 million years ago.

“What was missing was geological evidence of the onset” of uplift, Wichura said. “That doesn’t exist in this area, not in the normal geological sense.”

The fact that no indicative fossils were found can mostly be owed to the volatile environment that is East Africa – a hot spot in the mantle has been pushing magma upwards, thinning and spreading up a wide area, while rifts from tectonic forces have been breaking the crust apart. This doesn’t bode well for fossils, whose formations requires a relatively quiet and peaceful setting. This is where our whale steps in.

The original fossil catalogue from the Harvard Loperot Expedition in 1964. In the field the fossil specimen (14-64K) was mistakenly considered to be a turtle and later corrected to be a whale. Credit: Bryan Patterson

Beaked Whales

The fossil is the oldest known fossil of a beaked whale, and it surprised researchers at first. Beaked whales are divers that live in the oceans, but the fossil was found 460 miles (740 kilometers) inland from the present-day East African coast, and, to top it off, at an elevation of 2,100 feet (640 meters). How did the whale get all the way there? The most likely response seems to be that while it did live in the Indian Ocean, it ventured up a river in Africa.

A 17 million-year-old whale fossil stranded far inland in Kenya now sheds light on the timing and starting elevation of East Africa’s puzzling tectonic uplift, says paleontologist Louis Jacobs, Southern Methodist University, Dallas

“We came to the idea that it used a large river system, because the whale had been found in lake sediments which are [mixed with] river sediments,” Wichura said. “So we can say that it died in a kind of river-lake environment.”

But the fact that the whale traveled so much, not only in distance but also in elevation seems shocking. There is no recorded case of a whale swimming across such an elevation. Even the Antarctic minke, known for its very long travels of up to 600 miles (900 km) , only reached an elevation of little more than 3 feet above the Atlantic Ocean. A humpback whale, dubbed Humphrey, twice swam a more modest 82 miles (130 km) up the Sacramento River in California. Freshwater dolphins have been found at elevations of more than 300 feet (90 meters) in Peru. So it seems safe to say that this whale also couldn’t have swam so much uphill – so the uplift started after this whale’s adventure. This was the evidence Wichura and Jacobs were looking for.

It was time for a little math: today, the plateau is about 2,034 feet (620 m) tall. Considering the grade of the steepest river from case reports, the river couldn’t have rose by more than 2.5 inches a mile (4 centimeters per km) from the coast – this means that the East African plateau was between 79 feet and 121 feet high (24 m and 37 m) when the whale was there, so over the past 17 million years, the uplift amounted to about 1,925 feet (590 m). Everything seems to have started with the whale. Scientists know for sure the fossil was about 17 million years ago, because they found it in an undisturbed area just under a lava flow dated to 17 million years old. Around it were mammal fossils that date to a period when Africa and Eurasia were joined.

Without the whale, and without the collaborative study which involved structural geology, paleontology, biology and geography, scientists wouldn’t have been able to date the uplift.

Blainville’s beaked whale. Image via Wiki Commons.

“We knew it had to be after the big exchange between Eurasia and Africa, when elephants left Africa, and when carnivores and various kinds of hoofed animals came in,” 23 million years ago, Jacobs said.

The study reminds both professional and amateur paleontologists to study the location and age of each fossil they find, said Frank Brown, a professor of geology at the University of Utah, who was not involved in the study.

“Even single specimens of organisms tell us a great deal about the history of the Earth, and they sometimes appear in surprising cases,” Brown said. “This is one such case.”

Journal Reference: Henry Wichura, Louis L. Jacobs, Andrew Lin, Michael J. Polcyn, Fredrick K. Manthi, Dale A. Winkler, Manfred R. Strecker, and Matthew Clemens. A 17-My-old whale constrains onset of uplift and climate change in east Africa. doi: 10.1073/pnas.1421502112

 

Quartz may be key to plate tectonics

Plate tectonics is one of the most important theories, from the point of view of its practical effects on society – just look at the earthquake in Japan, or the iminent one in California, for example. More than 40 years ago, a man named J. Tuzo Wilson published a paper in Nature, describing how ocean basins open and close, in what is taught today in every geology course as the Wilson cycle. Basically, some ocean basins will shrink and become seas, or even disappear, and some sea basins will become ocean basins.

His observations, known today as the “Wilson Tectonic Cycle” suggested that this process took place numerous times in Earth’s troubled history, most recently when the supercontinent Pangaea split into the continents we know today. Wilson’s ideas are extremely important for plate tectonics, as well as the processes which lie at the very core of earthquake formation and mountain genesis.

Since his paper was published in 1967, pretty much every study conducted on the topic supported this idea, but few managed to bring additional information. Now, new findings by Utah State University geophysicist Tony Lowry and colleague Marta Pérez-Gussinyé of Royal Holloway, University of London offered an interesting point of view on the whole subject.

“It all begins with quartz,” says Lowry, who published results of the team’s recent study in the March 17 issue of Nature.

The scientists used and described a new way of measuring the properties of the rocks located beneath the deep crust. This way reveals events that cause the Earth’s surface to crack, fold and stretch, and it displays the key role played by quartz.

“If you’ve ever traveled westward from the Midwest’s Great Plains toward the Rocky Mountains, you may have wondered why the flat plains suddenly rise into steep peaks at a particular spot,” Lowry says. “It turns out that the crust beneath the plains has almost no quartz in it, whereas the Rockies are very quartz-rich.”

He believes that it’s exactly those belts of quartz that set in motion the chain of events which leads to the mountain building rock cycle.

“Earthquakes, mountain-building and other expressions of continental tectonics depend on how rocks flow in response to stress,” says Lowry. “We know that tectonics is a response to the effects of gravity, but we know less about rock flow properties and how they change from one location to another.”

“Over the last few decades, we’ve learned that high temperatures, water and abundant quartz are all critical factors in making rocks flow more easily,” Lowry says. “Until now, we haven’t had the tools to measure these factors and answer long-standing questions.”

But now, thanks to EarthScope, that has all changed.

“This intriguing study provides new insights into the processes driving large-scale continental deformation and dynamics,” says Greg Anderson, NSF program director for EarthScope. “These are key to understanding the assembly and evolution of continents.”

“We’ve combined Earthscope data with other geophysical measurements of gravity and surface heat flow in an entirely new way, one that allows us to separate the effects of temperature, water and quartz in the crust,” Lowry says.

They found that even at a low seismic velocity ratio, even after separating the temperatures, quartz-rich crust appears in pretty much the same places as high lower-crustal temperatures modeled independently from surface heat flow.

“That was a surprise,” he says. “We think this indicates a feedback cycle, where quartz starts the ball rolling.”

However, if the temperature and water are the same, rock flow will tend to focus on the quartz because that is the weak link.

“Rock, when it warms up, is forced to release water that’s otherwise chemically bound in crystals,” he says

More info about the Earth Scope Project here