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Ancient Fragment of The Pacific Ocean Found Buried 400 Miles Below China

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Scientists have identified an old piece of the Pacific Ocean – the ancient remains of its long-ago seabed – extending hundreds of miles underneath China, as it is pulled downward into Earth’s mantle transition zone.

 

This rocky slab that used to line the bottom of the Pacific is a relic of the oceanic lithosphere, the outermost layer of Earth’s surface, composed of the crust and the solid outermost parts of the upper mantle.

The lithosphere isn’t always destined to enjoy the views up top, however. The upper surface layer is composed of several fragmented tectonic plates, which slowly move and shift around at the surface, occasionally running into each other.

During these collisions, a geological process called subduction can occur, where one plate gets forced under the other at subduction zones, and ends up being driven ever deeper into the planet.

In a new study, scientists from China and the US have now witnessed this epic phenomenon taking place at greater depths than ever before observed.

Prior to this, scientists had recorded subducting slabs probing the boundaries at depths of about 200 kilometres (roughly 125 miles).

Now, thanks to giant network of over 300 seismic stations spread around northeastern China, researchers were able to see the event at a much lower point, imaging parts of the tectonic plate that used to lie under the Pacific Ocean being pushed into the mantle’s mid-level transition zone, at depths ranging between 410–660 kilometres (254–410 miles) below Earth’s surface.

Screenshot 2020 11 17 at 5.44.54 PM (Christoph Burgstedt/Science Photo Library)

To interpret the sinking slab, the team identified two seismic velocity discontinuities, regions far underground where seismic waves encounter anomalies. In this case, two anomalies were encountered, which the team says related to both the top and bottom sides of the plunging plate.

“Based on detail seismological analyses, the upper discontinuity was interpreted to be the Moho discontinuity of the subducted slab,” says geophysicist Qi-Fu Chen from the Chinese Academy of Sciences.

 

“The lower discontinuity is likely caused by partial melting of sub-slab asthenosphere under hydrous conditions in the seaward portion of the slab.”

While the plate’s subduction can be seen in process below China, the subduction zone itself lies far to the east, with the slab being angled at a relatively shallow 25-degree angle downwards.

“Japan is located about where the Pacific plate reaches around 100-kilometre depths,” says seismologist Fenglin Niu from Rice University.

Thanks to the new imaging, scientists are getting a better idea of what happens to a subducted slab when it reaches this part of the transition zone, including how deformed it gets, and how much water content it loses from its oceanic crust.

“A lot of studies suggest that the slab actually deforms a lot in the mantle transition zone, that it becomes soft, so it’s easily deformed,” Niu says.

“We are still debating whether this water is totally released in that depth. There is increasing evidence that a portion of the water stays inside the plate to go much, much deeper.”

The findings are reported in Nature Geoscience.

 



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Geologists Find Magma ‘Conveyor Belt’ That Fuelled Earth’s Longest Supervolcano Burst

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A subterranean ‘conveyor belt’ of magma, pushing up to Earth’s surface for millions of years, was responsible for the longest stretch of erupting supervolcanoes ever seen on the planet, according to new research.

 

Shifts in the seabed caused channels to form, through which the magma could flow freely, researchers say. This resulted in an extensive period of eruptions lasting from around 122 million years ago to 90 million years ago; exceptional, considering that typically these types of flows lasted just 1-5 million years.

This all took place on the Kerguelen Plateau, which now sits under the Indian Ocean. It’s what’s known as a large igneous province or LIP, a widespread accumulation of magma and lava. Scientists can use these LIPs to trace volcanic activity back through time.

“Extremely large accumulations of volcanic rocks – known as large volcanic provinces – are very interesting to scientists due to their links with mass extinctions, rapid climatic disturbances, and ore deposit formation,” says geologist Qiang Jiang, from Curtin University in Australia.

Jiang and his colleagues used samples of black basaltic rocks taken from the sea floor, together with an argon isotope dating method to determine the spread and rise of the LIP as it sat on what’s known as a mantle plume, created by rising magma.

 

Across the 30 or so years of intense activity, the Kerguelen Plateau rose by about 20 centimetres (7.87 inches) a year, the researchers say. Across the gigantic size of the LIP – about three times the size of Japan – the outpouring equates to lava filling 184,000 Olympic-sized swimming pools per year.

The Kerguelen Plateau saw such a long and steady run of supervolcano activity because of its unique configuration, the study suggests: a mantle plume combining with slow spreading mid-ocean ridges channelling the magma upwards.

“The volcanism lasted for so long because magmas caused by the mantle plume were continuously flowing out through the mid-oceanic ridges, which successively acted as a channel, or a ‘magma conveyor belt’ for more than 30 million years,” says geologist Hugo Olierook, from Curtin University.

“Other volcanoes would stop erupting because, when temperatures cooled, the channels became clogged by ‘frozen’ magmas. For the Kerguelen Plateau, the mantle plume acts as a Bunsen burner that kept allowing the mantle to melt, resulting in an extraordinarily long period of eruption activity.”

That’s a lot of volcanic eruption activity over many millions of years, but the rate dropped significantly about 90 million years ago, and scientists still aren’t sure why. Associated volcanic activity continues to this day, on a much smaller scale.

It’s a fascinating look at the past history of our planet, and of course it informs our study of volcanic activity in the present day too – the more we know about how these kinds of systems can form and stay active, the better we can understand the interactions taking place under the Earth’s surface right now.

“Finding this long, continuous eruption activity is important because it helps us to understand what factors can control the start and end of volcanic activity,” says geochronologist Fred Jourdan, from Curtin University.

“This has implications for how we understand magmatism on Earth, and on other planets as well.”

The research has been published in Geology.

 



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Giant Asteroid Survivor of Failed Planet Discovered to Be Slowly Rusting in Space

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Roughly two to three times Earth’s distance from the Sun, in the Asteroid Belt that lies between Mars and Jupiter, 16 Psyche makes its home. This giant metal asteroid is one of the most massive objects in the Asteroid Belt, categorised as a minor planet.

 

Astronomers think that 16 Psyche is the exposed core of a full planet that didn’t make it all the way, and we’re itching to know more about it. NASA will be sending a probe to check it out in the next few years, and in the meantime, scientists are working to glean what they can from Earth.

Now, for the first time, 16 Psyche has been studied in ultraviolet wavelengths using the Hubble Space Telescope, revealing that, just as we thought, the dense chunk of space rock is remarkably metallic.

“We’ve seen meteorites that are mostly metal, but Psyche could be unique in that it might be an asteroid that is totally made of iron and nickel,” said planetary scientist Tracy Becker of the Southwest Research Institute.

“Earth has a metal core, a mantle and crust. It’s possible that as a Psyche protoplanet was forming, it was struck by another object in our Solar System and lost its mantle and crust.”

16 Psyche is a pretty fascinating chunk of rock. It’s about 226 kilometres (140 miles) across, and just a little less dense than Earth. Its composition seems to consist of somewhere between 30 to 60 percent metal, and the rest low-iron silicate.

 

If 16 Psyche is a protoplanetary core, it’s possible such impacts stripped it of its accumulating material. Planets are thought to form when their stars are very young – possibly even in tandem – and are surrounded by a thick cloud of dust and gas. Material in this cloud starts to stick together, first electrostatically, then gravitationally as the object grows more massive.

As these bodies grow, they become hot and a bit molten, allowing material to move around. Core differentiation is the process whereby denser material sinks inwards towards the centre of the object, and less dense material rises outwards. For 16 Psyche to be a differentiated core, the protoplanet would once have had to have been much bigger than it is now.

Exactly when, and how, its outer mantle was stripped away is a bit of a head-scratcher. But Becker’s team’s research could be the breadcrumbs that put us on the trail to figuring it out.

“We were able to identify for the first time on any asteroid what we think are iron oxide ultraviolet absorption bands,” she said. “This is an indication that oxidation is happening on the asteroid, which could be a result of the solar wind hitting the surface.”

 

In other words, 16 Psyche is rusting. And we might be able to work out how old its surface is based on how much oxidation has occurred – which in turn could give us a timeline of when the asteroid was stripped of its outer material.

The asteroid’s high reflectivity at ultraviolet wavelengths suggests that it’s been a long time; usually, ultraviolet brightness is linked with space weathering. But we won’t know for sure until NASA’s Psyche probe reaches the asteroid sometime around 2026.

Scientists are also keen to get a closer look at 16 Psyche’s composition. There’s a lot of wiggle room between 30 and 60 percent metal that has made it hard to track down smaller pieces of rock that may have resulted from the impact fragmentation of the 16 Psyche’s mantle.

It was once thought that the relatively metallic mesosiderite meteorites were remnants of 16 Psyche, but more recent research has found the connection weak.

The work of Becker and her team revealed a spectrum that is consistent with pure iron, but that may be misleading – as little as 10 percent iron on the surface could dominate the ultraviolet spectrum. There are also very few analogous observations of planetary surfaces in ultraviolet against which to compare the new views of 16 Psyche.

So, we obviously just have to go and check it out with an actual orbiting probe, which in turn will indicate how well we’ve done trying to figure out this strange object from hundreds of millions of kilometres away. Whatever we learn, it’s going to be like looking at a Solar System time capsule. 

“What makes Psyche and the other asteroids so interesting is that they’re considered to be the building blocks of the Solar System,” Becker said.

“To understand what really makes up a planet and to potentially see the inside of a planet is fascinating. Once we get to Psyche, we’re really going to understand if that’s the case, even if it doesn’t turn out as we expect. Any time there’s a surprise, it’s always exciting.”

The research has been published in The Planetary Science Journal.

 



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Scientists Just Discovered New Zealand Sits on an Ancient Volcanic Super Plume

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Back in the 1970s, scientists came up with a revolutionary idea about how Earth’s deep interior works.

They proposed it is slowly churning like a lava lamp, with buoyant blobs rising as plumes of hot mantle rock from near Earth’s core, where rocks are so hot they move like a fluid.

 

According to the theory, as these plumes approach the surface they begin to melt, triggering massive volcanic eruptions. But evidence for the existence of such plumes proved elusive and geologists had all but rejected the idea.

Yet in a paper published on 27 May, we can now provide this evidence.

Our results show that New Zealand sits atop the remains of such an ancient giant volcanic plume. We show how this process causes volcanic activity and plays a key role in the workings of the planet.

Unusual vibrations

About 120 million years ago – during the time of dinosaurs in the Cretaceous period – vast volcanic eruptions under the ocean created an underwater plateau about the size of India.

Over time, it was broken up by the movements of tectonic plates. One fragment now lies beneath New Zealand and forms the Hikurangi Plateau.

file 20200520 152349 mtsh6d(Simon Lamb)

Above: This map of the southwest Pacific and New Zealand shows the dispersed fragments of a once giant oceanic plateau. Red arrows show the directions of seafloor spreading. Straight black lines show the areas measured in our study. 

We measured the speed of seismic pressure waves – effectively soundwaves – and how they travel through mantle rocks beneath the Hikurangi Plateau. These vibrations were triggered either by earthquakes or deliberate explosions and reached speeds of 9 kilometres per second.

 

It’s well known these waves, known as P-waves, travel in the uppermost mantle of the Earth at a remarkably constant speed: around 8.1 km per second (about 30,000 km per hour).

Even small deviations from this constant speed reveal important information about the state of the mantle rocks.

Since the late 1970s, fast P-wave speeds (8.7-9.0 km/s) had been reported from a depth of about 30 km under New Zealand’s eastern North Island. The seismic vibrations recorded in these early data were only travelling in one direction through a small part of the mantle, and the significance of the high speed was unclear.

Our new data is much more extensive, from a major seismic experiment in 2012 that spanned the southern North Island and offshore regions, including the Hikurangi Plateau.

It shows the speed of P-waves reached 9 km/s, regardless of the horizontal direction in which they travelled. But a careful analysis of vibrations triggered by deep earthquakes showed unusually low speeds for vibrations travelling in the vertical direction.

This reveals crucial information about how the mantle rocks have been stretched or squeezed by the huge forces inside the Earth, and this turns out to confirm the existence of the elusive plumes.

 

A seismic pancake

The pattern of seismic speeds we observed requires the mantle rocks beneath the Hikurangi Plateau to have been stretched and squeezed in much the same way as one might produce a pancake shape by flattening a rubber ball.

file 20200523 124845 10usggx(James Moore)

Above: Computer simulations of a plume of buoyant hot rock in the Earth’s mantle rising up towards the surface from the core-mantle boundary. In the later stages, the plume head collapses under gravity to form a pancake shape. 

When we carried out computer simulations of rising plumes in the mantle, we found they reproduced exactly this pancake flattening pattern, as the mushroom-shaped head of the plume spreads sideways and collapses near the surface.

We also looked at data from seismic experiments by international teams on other oceanic plateaux in the south-west Pacific region. Remarkably, both the Manihiki and Ontong-Java plateaux showed the same pattern as we observed beneath the Hikurangi Plateau.

P-waves travelled at the same high speeds regardless of the horizontal direction, but at significantly slower speeds in the vertical direction.

 

Reconstructing an ancient superplume

The major oceanic plateaux of the southwest Pacific are now dispersed, but we know how they once fitted together, about 120 million years ago. They formed a region underlain by a thick layer of volcanic rock, thousands of kilometres across.

file 20200527 141312 1bmtk8z(Simon Lamb, Author provided)

Above: This reconstruction of oceanic plateaux at 120 million years ago shows how they fitted together above the pancake-shaped head of a superplume. 

Our analysis shows this entire region lay above the single head of a giant plume – a superplume – which melted to produce massive lava outbursts over a geologically brief period of a few million years.

Siberia is the only other place on Earth where this pattern of P-wave speeds has been observed in the upper mantle. And it turns out this was also the scene of widespread volcanic eruptions about 250 million years ago, thought to be caused by the rise of a superplume.

This volcanic activity may have changed Earth’s climate and triggered a mass extinction that affected the evolution of life.

New Zealand and some scattered islands in the southwest Pacific are perched on the remains of what was once an immensely powerful geological force.

We don’t know whether this process is still ongoing today, but our new seismic technique for finding these superplume remnants may help us discover more – providing further insight into the many connections between the deep interior of our planet and what happens at the surface. The Conversation

Simon Lamb, Associate Professor in Geophysics, Te Herenga Waka — Victoria University of Wellington and Timothy Stern, Professor of Geophysics, Te Herenga Waka — Victoria University of Wellington.

This article is republished from The Conversation under a Creative Commons license. Read the original article.

 



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The World’s Largest Shield Volcano Isn’t What We Thought It Was

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Beneath the cyan and cerulean waters of the Northwestern Hawaiian Islands lurks a leviathan. Its true extent has been hidden for many years, but no more. What geologists have found is a marvel – the biggest, hottest known volcano in the world.

 

Startlingly, it’s more than twice the size of the previous record holder, Mauna Loa on the Island of Hawai’i. And it could change our understanding of the vast Hawaiian-Emperor seamount chain of volcanoes that span the North Pacific Ocean.

The new record-breaker spreads across around 148,000 cubic kilometres (35,507 cubic miles) beneath the waves of the Papahānaumokuākea Marine National Monument, compared to Mauna Loa’s 74,000.

Only relatively small rocky pinnacles known as the Gardner Pinnacles break the surface, giving the volcano its name – Pūhāhonu, the Hawai’ian word for ‘turtle rising for breath’.

“We are sharing with the science community and the public that we should be calling this volcano by the name the Hawaiians have given to it, rather than the western name for the two rocky small islands that are the only above sea level remnants of this once majestic volcano,” said geologist Michael Garcia of the University of Hawai’i at Manoa.

Back in the 1970s, low-resolution bathymetric data suggested Pūhāhonu was around 54,000 cubic kilometres in size, then thought to be the largest volcano before a more extensive survey of Mauna Loa revealed its true size.

 

Pūhāhonu only regains its crown after extensive surveys of the region added high-resolution bathymetric and multibeam sonar data to our existing understanding of the northwest Hawaiian Ridge, from which the volcano rises.

Geologists combined this with petrologic analyses of rock samples retrieved from the volcano, refining volume calculations and modelling based on these parameters.

“It has been proposed that hotspots that produce volcano chains like Hawai’i undergo progressive cooling over 1-2 million years and then die,” Garcia said.

“However, we have learned from this study that hotspots can undergo pulses of melt production. A small pulse created the Midway cluster of now extinct volcanoes and another, much bigger one created Pūhāhonu. This will rewrite the textbooks on how mantle plumes work.”

volc chonk(Garcia et al., EPSL, 2020)

Pūhāhonu is a shield volcano, between 12.5 and 14.1 million years old, formed by a single magma plume surging through the mantle. Over the millennia, this source gradually built the volcano to a height of 4,500 metres (14,764 feet) from its lowest point, spanning an area 275 kilometres (171 miles) long and 90 kilometres (56 miles) wide.

Chemical analysis of rock collected from the volcano revealed a higher concentration of an olivine mineral called forsterite than we’ve ever seen in a Hawaiian volcano. This mineral indicates magma on the higher end of the temperature range.

 

The calcium oxide content in the forsterite allowed the team to infer the depth at which it formed, confirming that it did form in magma. Simulations allowed the team to calculate the pressure at which the forsterite formed, and the temperature.

According to these calculations, the magma clocked in at 1,703 degrees Celsius (3,097 degrees Fahrenheit) – hotter than any other Hawaiian basalt. This extreme temperature is reflected in the volcano’s size, the researchers said.

It’s an impressive beast in its own right. But it also has important implications for our understanding of the processes that create these incredible formations.

“The Hawaiian-Emperor Chain is arguably the world’s best studied surface expression of a mantle plume,” the researchers wrote in their paper.

“Nonetheless, new insights into its magmatic and thermal history continue to be revealed as more of the Hawaiian-Emperor Chain is mapped and sampled. These insights are providing a more complete understanding of the mechanics and thermal evolution of mantle plumes.”

The research has been published in Earth and Planetary Science Letters.

 



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An Ancient Meteorite Is The First Chemical Evidence of Volcanic Convection on Mars

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For many years, we thought Mars was dead. A dusty, dry, barren planet, where nothing moves but the howling wind. Recently, however, pieces of evidence have started to emerge, hinting that Mars is both volcanically and geologically active.

 

Well, the idea of a volcanically active Mars just got a little more real. A meteorite that formed deep within the belly of Mars has just provided the first solid chemical proof of magma convection within the Martian mantle, scientists say. 

Crystals of olivine in the Tissint meteorite that fell to Earth in 2011 could only have formed in changing temperatures as it was rapidly swirled about in magma convection currents – showing that the planet was volcanically active when the crystals formed around 574 to 582 million years ago – and it could still be intermittently so today.

“There was no previous evidence of convection on Mars, but the question ‘Is Mars a still volcanically active planet?’ was previously investigated using different methods,” explained planetary geologist Nicola Mari of the University of Glasgow to ScienceAlert.

“However, this is the first study that proves activity in the Mars interior from a purely chemical point of view, on real Martian samples.”

Olivine, a magnesium iron silicate, isn’t rare. It crystallises from cooling magma, and it’s very common in Earth’s mantle; in fact, the olivine group dominates Earth’s mantle, usually as part of a rock mass. On Earth’s surface, it’s found in igneous rock.

 

It’s fairly common in meteorites. And olivine is also fairly common on Mars. In fact, the presence of olivine on the surface of Mars has previously been taken as evidence of the planet’s dryness, since the mineral weathers rapidly in the presence of water.

But when Mari and his team started studying the olivine crystals in the Tissint meteorite to try to understand the magma chamber where it formed, they noticed something strange. The crystals had irregularly spaced phosphorus-rich bands.

We know of this phenomenon on Earth – it’s a process called solute trapping. But it was a surprise to find it on Mars.

magma olivine(Mari et al., Meteoritics & Planetary Science, 2020)

“This occurs when the rate of crystal growth exceeds the rate at which phosphorus can diffuse through the melt, thus the phosphorus is obliged to enter the crystal structure instead of ‘swimming’ in the liquid magma,” Mari said.

“In the magma chamber that generated the lava that I studied, the convection was so vigorous that the olivines were moved from the bottom of the chamber (hotter) to the top (cooler) very rapidly – to be precise, this likely generated cooling rates of 15-30 degrees Celsius per hour for the olivines.”

 

The larger of the olivine crystals were also revealing. Traces of nickel and cobalt are in agreement with previous findings that they originated from deep under the Martian crust, a depth of 40 to 80 kilometres (25 to 50 miles).

This supplied the pressure at which they formed; along with the equilibration temperature of olivine, the team could now perform thermodynamic calculations to discover the temperature in the mantle at which the crystals formed.

They found that the Martian mantle probably had a temperature of around 1,560 degrees Celsius in the Martian Late Amazonian period when the olivine formed. This is very close to the ambient mantle temperature of Earth of 1,650 degrees Celsius during the Archean Eon, 4 to 2.5 billion years ago.

That doesn’t mean Mars is just like an early Earth. But it does mean that Mars could have retained quite a bit of heat under its mantle; it’s thought that, because it lacks the plate tectonics that help to dissipate heat on Earth, Mars may cool more slowly.

“I really think that Mars could be a still volcanically active world today, and these new results point toward this,” Mari told ScienceAlert.

“We may not see a volcanic eruption on Mars for the next 5 million years, but this doesn’t mean that the planet is inactive. It could just mean that the timing between eruptions between Mars and Earth is different, and instead of seeing one or more eruptions per day (as on Earth) we could see a Martian eruption every n-millions of years.”

We’ll need more research to confidently say this hypothesis checks out. But these results also mean that previous interpretations of the planet’s dryness based on surface olivine may need to be revisited. (Although let us be clear, Mars is still extremely dry.)

The ongoing NASA InSight mission that recently found evidence of Marsquakes, measures – among other things – the heat flux from the Martian crust. If Mars is still volcanically active, we may know more about it really soon.

The research has been published in Meteoritics & Planetary Science.

 



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Earth’s Core Could Be Leaking Heavy Iron Isotopes, New Study Reveals

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What goes down at the very center of our planet is largely a mystery, and so is what goes up.

The truth is, no human has ever made it past the crust, or dug deep enough to penetrate Earth’s rocky mantle, let alone its liquid iron core, so we don’t know what type of interactions take place here. And that’s not for a lack of trying.

 

Sitting at a depth of roughly 2,900 kilometres (1,800 miles), our planet’s core lies far beyond our technological reach – at least for now – and yet through educated guesswork and clever theoretical models, scientists have drawn a window into some of the enigmas lying beneath our feet.

New research now suggests Earth’s molten core may actually be leaking iron into the upper mantle, which is more than a thousand degrees cooler than the liquid nucleus.

For decades, scientists have debated whether or not the core and the mantle exchange physical material.

Earth’s powerful magnetic field and its electric currents certainly imply there’s lots of iron down in the core. Plus, samples of mantle rocks brought to the surface show a significant chunk of iron as well, leading some to speculate the material is coming all the way from the core.

To gain some insight into whether this could be possible, researchers have drawn on experiments in the lab showing how iron isotopes move between areas of different temperatures under high pressure and temperature. 

heavyironiso(L. O’Dwyer Brown, Aarhus University)

Using this information to create a model, the team’s results suggest that heavy iron isotopes could be migrating from the Earth’s hot core out to the cooler mantle. While the light iron isotopes would do the opposite and move from cool to hot back down into the core.

These results are still theoretical, but they could teach us something important about how our planet’s interior works.

 

“If correct, this stands to improve our understanding of core-mantle interaction,” says geologist and petrologist Charles Lesher from Aarhus University in Denmark.

And that sort of knowledge is really important. It can help us interpret seismic images in the deep mantle and allow us to model how chemicals and heat rise and fall between Earth’s layers.

Using computer simulations, the authors were even able to show how this core material can make it all the way up to Earth’s surface, with heavier isotopes essentially hitching a ride on the upwells of a hot mantle plume, like those found in Samoa and Hawaii – a possible signature of Earth’s leaky core. 

A study published last year suggested something similar. Its authors found core material – in this case, tungsten isotopes – were also transferred to the surface via ascending mantle plumes and that the core has probably been leaking this material for the past 2.5 billion years or so.

Lesher says his results also suggest iron isotopes from the core have been leaking into the mantle for billions of years. But if exchanges like this are actually happening, the question then becomes: What is the impact over the long run?

 

Right now, no one really knows. The new simulation only shows that a leak from the core to the mantle under high temperature and pressure is possible, and it could explain why mantle rocks hold so much more iron than meteorites: in short, the iron liquid is coming from the heart.

The authors admit there’s considerable uncertainty in some of their model’s parameters, like diffusion, thermal conductivity or the amount of core liquid that’s actually infiltrating the mantle. The numbers chosen may not represent the reality of the situation. 

Nevertheless, the exchange of iron isotopes across the core-mantle barrier by thermodiffusion appears more than capable of iron-ing out our mantle, so to speak.

“This does not preclude other processes but simply shows that thermodiffusion is a plausible agent of isotopic fractionation in the region of the [core-mantle-barrier] on geological timescales,” the authors conclude.

The study was published in Nature Geoscience.

 



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Mars Could Have at Least Two Ancient Reservoirs of Water Deep Underground

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Mars. Water. You’d never find two more unlikely companions, even in a buddy cop movie. But once upon a time, the dry, red dustbowl of Mars was lush and soggy.

We’re still unravelling the history of that water, and planetary scientists have just discovered at least two distinct reservoirs of ancient water could be preserved under the Martian surface, with different chemical signatures.

 

This finding indicates that, unlike Earth, Mars probably didn’t have one big global ocean of underground magma encircling the entire planet.

“A lot of people have been trying to figure out Mars’ water history,” explained planetary scientist Jessica Barnes of the University of Arizona.

“Where did water come from? How long was it in the crust (surface) of Mars? Where did Mars’ interior water come from? What can water tell us about how Mars formed and evolved?”

The evidence was found in Mars rocks. We can’t exactly nip over to Mars and fetch them; indeed, to date we haven’t even conducted a robotic Mars sample return mission. But occasionally, Mars comes to us anyway.

Meteorites broken off from the Martian crust will, from time to time, make their way to Earth. Here in Earth labs, using state-of-the-art techniques, researchers carefully studied two such meteorites – Allan Hills 84001, discovered in Antarctica 1984, and Northwest Africa 7034, discovered in the Sahara Desert in 2011.

The team looked at the isotopes of hydrogen locked inside the Mars rocks. Isotopes are variants of an element with different numbers of neutrons; deuterium – also known as heavy hydrogen – has one proton and one neutron. Protium, or light hydrogen, has one proton and no neutrons.

 

Because hydrogen is one of the components of water, the ratio of these two isotopes locked in rocks can help us to understand the history of the water they were in – it’s like a fossil of water, an imprint of its presence that can be analysed to learn the chemical processes it was subject to, and its origins.

Barnes and her team are not the first to study hydrogen isotopes in Martian meteorites in order to try to learn about the planet’s water. But previous results have been scattered and inconsistent.

Here on Earth, protium is the dominant hydrogen isotope. That’s true for the atmosphere (although there’s not much hydrogen there), the water hydrogen in rocks, and the water in the ocean.

On Mars, deuterium is the dominant hydrogen isotope in the atmosphere, likely because solar radiation is stripping the protium – but isotope ratios in the rocks tested by scientists have run from Earth-like to Mars-like.

So, Barnes and her team decided to take a closer look at meteorites they knew for a certainty originated in the Martian crust.

 

Allan Hills 84001, according to previously conducted radioactive decay dating techniques, interacted with fluid in the Martian crust around 3.9 billion years ago. Similar analysis determined that Northwest Africa 7034 interacted with fluid 1.5 billion years ago.

When Barnes and her team conducted their isotope analysis, they found that both samples had similar isotope ratios, sitting comfortably in between the ratio found in Earth’s water and the ratio found in the Martian atmosphere. Even more peculiarly, this ratio was similar to younger rocks analysed by the Curiosity rover right there on Mars.

This indicates that the chemical composition of that water has been consistent for around 3.9 billion years – a completely unexpected result, given the previous research

“Martian meteorites basically plot all over the place, and so trying to figure out what these samples are actually telling us about water in the mantle of Mars has historically been a challenge,” Barnes said.

“The fact that our data for the crust was so different prompted us to go back through the scientific literature and scrutinise the data.”

But when the team compared their results with previous research on hydrogen isotopes in meteorites from the Martian mantle – below the crust – they found something really surprising. Mantle meteorites fit into two distinct groups of igneous rock called shergottite.

Enriched shergottite has more deuterium; depleted shergottite has less deuterium. Average out their two ratios, and you get the crustal ratio seen in Allan Hills 84001 and Northwest Africa 7034.

Those two distinct chemical signatures indicate two different, unmixed reservoirs of water in the Martian mantle. Which may mean that, unlike Earth, a global ocean of liquid magma below the mantle did not homogenise the layer above.

“These two different sources of water in Mars’ interior might be telling us something about the kinds of objects that were available to coalesce into the inner, rocky planets,” Barnes said.

“This context is also important for understanding the past habitability and astrobiology of Mars.”

The research has been published in Nature Geoscience.

 



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The Strangest Field of Astronomy You’ve Never Heard Of

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In 2015, astronomers found something weird. It was a white dwarf star, 570 light-years from Earth, with a peculiar dimming pattern. It dimmed several times to varying depths, each depth repeating on a 4.5 to 5-hour timeframe; and its atmosphere was polluted with elements usually found in rocky exoplanets.

 

It didn’t take long before they figured it out. The gravity of the dead star was in the process of shredding and devouring bodies in orbit around it, a violent process known rather politely as tidal disruption.

The star is called WD 1145+017, and it’s now being used as a proof of concept for a new field of planet study, forensic reconstruction of planetary bodies to understand what they were like, and how they died.

Astronomers from the US and the UK are calling this field necroplanetology.

Their analysis of WD 1145+017 has been accepted into The Astrophysical Journal, and is available on arXiv. And it could, the researchers say, be applied to future discoveries similar to the white dwarf system to piece together how planets die orbiting different kinds of dead stars.

Although white dwarfs eject a lot of material when they die in a series of violent thermonuclear explosions, planets can somehow survive the process. Not only have we found planets in orbit around white dwarf stars, we have found elements in the atmospheres of white dwarf stars that are usually found inside rocky exoplanets.

 

The surface gravity of white dwarfs is so intense that these heavier elements would sink quite quickly, indicating that the star must have accreted the material quite recently, from a body that survived the star’s death throes.

To try and determine how WD 1145+017 got the way it did, astronomers from the University of Colorado, Boulder, Wesleyan University, and the University of Warwick in the UK conducted a series of simulations to place constraints on the tidally disrupted body.

They tweaked structural components of an orbiting body, such as the size of the core and mantle; the composition of the mantle, rocky or icy; and the presence of a crust. This resulted in 36 different simulated bodies.

Then, they set each of these 36 bodies orbiting a star like WD 1145+017, around 60 percent of the mass of the Sun, and 2 percent of its size (white dwarfs are pretty dense).

This orbit was 4.5 hours, as per the material orbiting WD 1145+017, and each simulation ran for 100 orbits. And finally, the resulting light curves for the tidal disruption of each body were then compared with the real-life light curve of WD 1145+017.

 

These simulations showed that the bodies most likely to produce what we observe in WD 1145+017 have a small core, and a low-density mantle, “resembling an asteroid with a partially differentiated structure and volatile-rich mantle like Vesta,” the researchers wrote in their paper.

The bodies are relatively low mass, and have bulk density high enough to maintain structure for a while, but low enough that their mantles are disrupted. These attributes are consistent with the lack of small particles found in other observations of the star, since these would sublimate quickly.

And, in fact, they offer some clues as to other mysterious stars as well – such as the famous KIC 8462852, AKA Tabby’s star, whose inconsistent dimming is a source of much puzzlement among astronomers.

KIC 8462852, since its strange behaviour was first discovered, has turned out not to be the only star exhibiting such strange dimming. A survey last year turned up another 21 strangely dimming stars that could have similar dynamics.

And other white dwarfs slurping down orbiting bodies have been discovered, too. ZTF J0139+5245 and WD J0914+1914 were both discovered tidally disrupting planets last year.

These stars could be simulated using the team’s new methods, too.

“These are the first members of a larger class of dying planetary systems that must be studied by pairing spectroscopic and photometric observations with disruption simulations, either tidal as in WD 1145+017 or rotational as Veras et al. (2020) proposes for the body transiting ZTF J0139+5245,” the researchers wrote in their paper.

“This multi-pronged approach would use the death of these planetary systems in action to study fundamental properties of exoplanetary bodies that are otherwise inaccessible: a study in necroplanetology.”

The research has been accepted into The Astrophysical Journal, and is available on arXiv.

 



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The Fragment of an Ancient Lost Continent Has Been Discovered Off The Coast of Canada

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Scientists have uncovered a splintered remnant of Earth’s continental crust from millions of years ago, embedded in the isolated wilderness of northern Canada.

Baffin Island, located in between the Canadian mainland and Greenland, is a vast Arctic expanse covering over 500,000 square kilometres (almost 200,000 square miles), making it the fifth largest island in the world.

 

While the island comprises part of the newest recognised territory in Canada – Nunavut, formally established in 1999 – a new discovery shows this ancient landmass has undisclosed ties that stretch backwards in time so far, they actually emanate from a distant geologic eon.

While analysing igneous rock samples recovered from diamond exploration drilling in the Chidliak Kimberlite Province at the southern stretches of Baffin Island, researchers identified a mineral signature in the rock they had never expected to find.

“Kimberlites are subterranean rockets that pick up passengers on their way to the surface,” explains geologist Maya Kopylova from the University of British Columbia.

“The passengers are solid chunks of wall rocks that carry a wealth of details on conditions far beneath the surface of our planet over time.”

In this case, those passengers had completed a very long journey. The team says kimberlite rocks like this, formed at depths below 150 kilometres (93 miles), are driven to the surface by both geological and chemical forces.

In terms of the geological component, their emergence underneath modern-day Baffin Island represents the end of a colossal dispersal that occurred approximately 150 million years ago, during rifting of the continental plate of the North Atlantic Craton (NAC).

 

This NAC refers to chunks of lithospheric rock that date back billions of years ago to the Archean Eon, representing some of the best exposures of Earth’s earliest continental crust.

Rifted into fragments millions of years ago, NAC has been exposed in Scotland, Labrador, and Greenland, but researchers weren’t expecting to find it in Baffin Island’s Hall Peninsula.

“The mineral composition of other portions of the North Atlantic Craton is so unique there was no mistaking it,” says Kopylova.

“It was easy to tie the pieces together. Adjacent ancient cratons in Northern Canada – in Northern Quebec, Northern Ontario and in Nunavut – have completely different mineralogies.”

To reach their findings, the team used a number of analytical techniques – including petrography, mineralogy, and thermobarometry – to study 120 rock samples, called xenoliths, taken from the kimberlite province.

The results showed the Chidliak mantle “strikingly resembles” the NAC rocks from West Greenland in terms of their bulk composition and mineral chemistry, while showing numerous contrasts with markers from other cratons.

“We conclude that the Chidliak mantle demonstrates an affinity with only one adjacent block of cratonic mantle, the NAC,” the authors explain in their paper.

 

“We interpret this similarity as indicating the former structural coherence of the cratonic lithosphere of the Hall Peninsula Block and the NAC craton prior to subsequent rifting into separate continental fragments.”

The new findings mean we’ve discovered about 10 percent more of the known expanse of the NAC – a pretty sizeable chunk of this incredibly ancient crust. And thanks to newer mantle modelling techniques, we can also envisage the shape of some of Earth’s earliest known rock formations at much greater depths than ever before.

“With these samples we’re able to reconstruct the shapes of ancient continents based on deeper, mantle rocks,” says Kopylova.

“We can now understand and map not only the uppermost skinny layer of Earth that makes up one percent of the planet’s volume, but our knowledge is literally and symbolically deeper.”

The findings are reported in Journal of Petrology.

 



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