Tag Archives: Core

Earth’s inner core may be actually made of two layers

Physicists at the Australian National University (ANU) have made a groundbreaking find: Earth’s inner core is made of two distinct layers.

“We found evidence that may indicate a change in the structure of iron, which suggests perhaps two separate cooling events in Earth’s history,”  Joanne Stephenson, lead author of the new study, said in a statement.

When Earth formed more than 4.5 billion years ago, it was still a planet-sized blob of molten rock. But once the planet cooled down, it started to first form the outer crust, then the mantle, the outer core, and the inner core.

The inner core is actually solid despite it’s hotter than the sun’s surface thanks to the atomic diffusion of iron at high pressure. Meanwhile, the outer core is liquid, made of molten iron in constant churning movement, driven by convection as the outer core loses heat to the static mantle. This process is what generates the planetary magnetic field akin to a dynamo.

We know so many intimate details about Earth’s distinct layers — even though they’re obscured by 6,353 kilometers of rock — by inferring their properties from acoustic waves passing through. When an acoustic wave generated by a volcanic eruption or earthquake is propagated below the surface, its properties such as direction, angle, and velocity change as a function of the material it encounters. 

Thanks to such investigations, scientists have long known that Earth’s solid inner core is nearly the size of the moon and is mostly made of crystallized iron — but that’s not all.

New findings set to rewrite textbooks suggest that there’s an innermost layer in the inner core. The researchers speak of evidence pointing to a change in the structure of iron at a depth of around 5,800 kilometers.

“The idea of another distinct layer was proposed a couple of decades ago, but the data has been very unclear,” Stephenson said.

“We got around this by using a very clever search algorithm to trawl through thousands of the models of the inner core.”

If confirmed, it means that the two layers must have been created by two separate major cooling events in the planet’s history. The precise details, however, are still a mystery.

Previously, researchers suspected that there may be more to Earth’s inner core than meets the eye due to experiments showing inconsistencies in our planetary model. Some believe that the first-generation iron crystals in the innermost core may have different structural alignments.

The findings appeared in the Journal of Geophysical Research.

 

In the Earth’s core, it’s snowing iron

Christmas is just around the corner, and with it, inevitably, come songs of “let it snow”. This particular carol is also relevant at the Earth’s core, a new study shows. According to the findings, iron snow blankets our planet’s internal core year-round.

Image credits Hendrik Kueck / Flickr.

Extreme pressure and heat don’t rule out snow, it seems, but it does make it more metal. Particles of iron that form in the Earth’s outer core ‘snow down’ on top of the inner core, a new study reports, and pile up in layers up to 200 miles thick.

The Earth’s inner core is hot, under immense pressure and snow-capped, according to new research that could help scientists better understand forces that affect the entire planet.

The snow is made of tiny particles of iron — much heavier than any snowflake on Earth’s surface — that fall from the molten outer core and pile on top of the inner core, creating piles up to 200 miles thick that cover the inner core. The findings could help explain anomalies seen in geophysical systems and improve our understanding of the processes taking place in the heart of our planet.

Inside knowledge

“The Earth’s metallic core works like a magma chamber that we know better of in the crust,” said Jung-Fu Lin, a professor in the Jackson School of Geosciences at The University of Texas at Austin and a co-author of the study.

Since the Earth’s interior is a tad inaccessible to us, researchers use seismic waves to investigate its structure and behavior. We know how seismic waves act in different contexts from experiments done on the surface, so we can estimate how they will behave inside the planet based on our current models of Earth’s structure. Whenever we see something that doesn’t go according to our predictions, it’s a good sign that our model was wrong — and we update it to fit the results.

One area where our predictions didn’t match results is at the boundary between the outer and inner core. Seismic waves move more slowly through this area than we expected, and move faster than we thought they would through the eastern hemisphere of the topmost inner core.

The study proposes that the layers of ‘iron snow’ that form on the core can explain the results. The existence of this slurry-like layer has been suggested since the early 1960s, but the data needed to support this view proved elusive.

In the study, Zhang and his team explain that crystallization was possible in this layer of the Earth and that about 15% of the lowermost outer core could be made up of iron-based crystals. It’s these crystals that fall down and settle onto the liquid inner core like a blanket of snow. This build-up is the cause of the anomalous seismic readings in the area, they add.

“It’s sort of a bizarre thing to think about,” said Nick Dygert, an assistant professor at the University of Tennessee who co-authored the study. “You have crystals within the outer core snowing down onto the inner core over a distance of several hundred kilometers.”

Seismic waves move faster through denser material — and the slurry-like coating of iron crystals slows them down. Because there is a variation in the thickness of these deposits around the inner core, with the eastern hemisphere showing thinner packs, seismic wave speed isn’t constant throughout the boundary.

“The inner-core boundary is not a simple and smooth surface, which may affect the thermal conduction and the convections of the core,” Zhang said.

The Earth’s core is the lynchpin in phenomena that affect the planet as a whole, from supplying the heat that drives plate tectonics to the generation of its magnetic field. Better understanding its structure and properties can help us make better sense of the processes it partakes in — and of other planets as well.

The paper “Fe Alloy Slurry and a Compacting Cumulate Pile Across Earth’s Inner‐Core Boundary” has been published in the Journal of Geophysical Research: Solid Earth.

Earth’s core is a lot like oil and vinegar — in a way

What does salad dressing have to do with the core of our planet? Quite a bit, according to a new study, and it’s got a lot to do with the Earth’s magnetic field.

A laser-heated diamond anvil cell is used to simulate the pressure and temperature conditions of Earth’s core. Top right inset shows a scanning electron microscope image of a quenched melt spot with immiscible liquids. Image credits: Sarah M. Arveson / Yale University.

Earth’s magnetic field, produced near the center of the planet, is essential to the survival of all life on the planet, acting as a protective shield from the harmful radiation of solar winds emanating from the Sun. However, our knowledge of Earth’s magnetic field and its evolution is incomplete. A new study finds that this evolution might have a lot to do with a process called immiscibility.

Miscibility is the property of two substances to mix, forming a homogeneous solution. When two substances are immiscible, they don’t mix — think of oil and water or oil and vinegar, for instance. Yale associate professor Kanani K.M. Lee and her team published a new study which suggests that molten iron alloys containing silicon and oxygen form two distinct liquids in the Earth’s core — two immiscible fluids, which just don’t mix together.

“We observe liquid immiscibility often in everyday life, like when oil and vinegar separate in salad dressing. It is surprising that liquid phase separation can occur when atoms are being forced very close together under the immense pressures of Earth’s core,” said Yale graduate student Sarah Arveson, the study’s lead author.

We’ve known for quite a while that the outer core has two major layers. Seismic waves traveling through the outer part of the outer core move slower than in the inner parts. Scientists have several theories explaining what is causing this slower layer, including immiscible fluid. However, until now, there was no experimental evidence to support this idea. In the new study, Lee and colleagues used laser-heated, diamond-anvil cell experiments to generate high pressures and temperatures, mimicking the conditions of the outer core. They found that under these conditions, two distinct, molten fluid layers are formed: an oxygen-poor, iron-silicon fluid and an iron-silicon-oxygen fluid. Because the iron-silicon-oxygen layer is less dense, it rises to the top, forming an oxygen-rich layer of fluid.

“Our study presents the first observation of immiscible molten metal alloys at such extreme conditions, hinting that immiscibility in metallic melts may be prevalent at high pressures,” said Lee.

This is important for the Earth’s magnetic field because most of it is believed to be generated in this outer core as the hot fluid in this layer roils vigorously as it convects.

This still doesn’t completely solve the puzzle of our planet’s magnetic field, but it offers an important puzzle piece.

The study has been published in the Proceedings of the National Academy of Sciences

Sunset.

Massive solar storms are naturally-recurring events, study finds — and we’re unprepared for them

Solar storms can be even more powerful than what our measurements so far have indicated — and we’re still very unprepared.

Sunset.

Image via Pixabay.

Although our planet’s magnetic field keeps us blissfully unaware of it, the Earth is constantly being pelted with cosmic particles. Sometimes, however — during events known as solar storms, caused by explosions on the sun’s surface — this stream of particles turns into a deluge and breaks through that magnetic field.

Research over the last 70 years or so has revealed that these events can threaten the integrity of our technological infrastructure. Electrical grids, various communication infrastructure, satellites, and air traffic can all be floored by such storms. We’ve seen extensive power cuts take place in Quebec, Canada (1989) and Malmö, Sweden (2003) following such events, for example.

Now, new research shows that we’ve underestimated the hazards posed by solar storms — the authors report that we’ve underestimated just how powerful they can become.

‘Tis but a drizzle!

“If that solar storm had occurred today, it could have had severe effects on our high-tech society,” says Raimund Muscheler, professor of geology at Lund University and co-author of the study. “That’s why we must increase society’s protection again solar storms.”

Up to now, researchers have used direct instrumental observations to study solar storms. But the new study reports that these observations likely underestimated how violent the events can become. The paper, led by researchers at Lund University, analyzed ice cores recovered from Greenland to study past solar storms. These cores formed over the last 100,000 years or so, and have captured evidence of storms over that time.

According to the team, the cores recorded a very powerful solar storm occurring in 600 BCE. Also drawing on data recovered from the growth rings of ancient trees, the team pinpointed two further (and powerful) solar storms that took place in 775 and 994 CE.

The result thus showcases that, although rare, massive solar storms are a naturally recurring part of solar activity.

This finding should motivate us to review the possibility that a similar event will take place sooner or later — and we should prepare. Both the Quebec and Malmö incidents show how deeply massive solar storms can impact our technology, and how vulnerable our society is to them today.

“Our research suggests that the risks are currently underestimated. We need to be better prepared,” Muscheler concludes.

The paper “Multiradionuclide evidence for an extreme solar proton event around 2,610 B.P. (∼660 BC)” has been published in the journal Proceedings of the National Academy of Sciences.

Magnetic lines.

Earth’s inner core became solid just in time to save the planet

The Earth’s solid core likely formed about 565 million years ago, new research reveals — saving Earth’s magnetic shield in the process.

Magnetic lines.

Image credits Windell Oskay / Flickr.

Earth’s magnetic field forms a veritable bulwark against charged particles coming from space — such as solar wind and rays of cosmic radiation — that would otherwise turn us all to crispy mush. It also safeguards Earth’s atmosphere, which would be flayed little by little by these same solar winds in its absence. So if you enjoy breathing, you should be a big fan of the Earth’s magnetic field.

Our planet hasn’t always enjoyed the magnetic field protection of today, however. New research suggests that it’s only been around for roughly 565 million years.

Restarting the dynamo

The Earth’s magnetic field was at its lowest intensity around that time, the authors of a new study report. This suggests our planet’s internal dynamo was close to collapsing at that date (since this dynamo is what generates the planet’s magnetic field). The formation of Earth’s solid inner core was the one event that could strengthen this geomagnetic field, so this could not have happened yet.

As such, the team proposes that the planet’s inner core had begun to solidify around this time, although the process was not complete. These results should help refine our current estimates of when Earth’s inner core solidified. Currently, these estimates range between 2.5 billion and 500 million years ago.

For the study, John Tarduno and colleagues measured the geomagnetic field’s past intensity and direction. They did this by looking at tiny magnetic inclusions found within single crystals of plagioclase and clinopyroxene formed 565 million years ago in what is now Canada’s eastern Quebec. Think of these inclusions — usually iron compounds — as tiny compass needles, aligning themselves to the magnetic field as the crystals formed. By studying them, the team could determine the direction and intensity of the magnetic field at the date of the crystals’ formation.

They found unprecedentedly low geomagnetic field intensities. From this, they inferred that there was a high frequency of magnetic reversals at that time, suggesting that the geodynamo was on the point of collapsing. Iron solidifying at the (fledgling) inner core boundary would have injected significant energy into the dynamo system by driving the currents of liquid metal that generate the magnetic field. Computer simulations predicted that this energy boost would be preserved in the rock record, which determines the team to look for evidence in ancient crystals.

In a News & Views article detailing the studies, Peter Driscoll writes that “the nucleation of the inner core may have occurred right in the nick of time to recharge the geodynamo and save Earth’s magnetic shield.”

The paper “Young inner core inferred from Ediacaran ultra-low geomagnetic field intensity” has been published in the journal Nature.