The magnetic fingerprint

Back in 1963, Frederick Vine and Drummond Matthews came up with a groundbreaking idea (pun very much intended); that the Earth's crust is divided into a bunch of chunks called plates that are all moving relative to each other, and that this is what causes virtually all earthquakes and volcanoes.

The main evidence for this dramatic paradigm shift in our understanding of how geology works came from the discovery on the ocean floor of regions of hardened lava that have opposite magnetic signatures.  When molten rock freezes, tiny magnetic particles that were free to move when they were in a liquid become locked into place, acting like billions of little compass needles recording the direction of the Earth's magnetic field at the time.  As you undoubtedly know, the positions of the magnetic poles flip, on average every three hundred thousand years (although the actual intervals vary greatly, for reasons that are still unknown).  So the rocks Vine and Matthews studied, on either side of the Mid-Atlantic Ridge, which showed symmetrically-arranged parallel stripes of magnetic signatures, showed that new oceanic crust was being formed all the time at the ridge, driving the plates apart and gradually widening the Atlantic Ocean.

Well, it turns out that lava isn't the only thing that can record what the magnetic field is doing.  According to a study last week in Proceedings of the National Academy of Sciences, so can pottery.

When clay is fired, its chemical structure changes, fusing into ceramic.  Different clays fire to different temperatures; in our kiln we fire our work to 1220 C (2232 F), which works for the clays classified as stonewares and mid-fire porcelains.  If we were to fire a high-fire porcelain to that temperature, it would still be brittle and not water-tight; fire an earthenware clay to that temperature, and it (literally) would melt.  (The difference is in the formulation of the clay, which is a complex subject about which I am still learning.)

But when you fire any clay to the correct temperature for that type, it effectively turns to stone.  The particles fuse together, giving it strength and resistance to breaking.  And this has the effect of locking into place any magnetic particles the clay may contain -- same as with Vine and Matthews's solidified lava on the ocean floor.

White stoneware vase with a cobalt splatter glaze

The reason this topic comes up is the discovery by a research team out of University College London of the fact that some earthenware bricks dating to the reign of Nebuchadnezzar II of Babylon (605-562 B.C.E.) show a magnetic particle pattern indicating a strange and sudden surge in the strength of the magnetic field -- something that has been nicknamed the Levantine Iron Age Geomagnetic Anomaly.

"It is really exciting that ancient artifacts from Mesopotamia help to explain and record key events in Earth history such as fluctuations in the magnetic field," said study co-author Mark Altaweel.  "It shows why preserving Mesopotamia’s ancient heritage is important for science and humanity more broadly."

Noting this odd magnetic fingerprint -- the cause of which is as yet unexplained -- has another added benefit; once they've identified it in items of known age (as with the bricks, that had an identifying stamp), it can be used to date ceramic items that have no such marks.

It makes me wonder what kind of record I'm creating in my own pottery.  When we have pieces with too many flaws to be worth keeping, we shatter them against the cement wall along the back of our house (there's now a pile of pottery shards at the base of the wall).  We think of it as our ongoing effort to confuse future archaeologists.  But supposing they do piece together some of our failed attempts at bowls and mugs and various sculptures, maybe they'll find out something more than our dubious skill at making pottery -- but what the Earth itself was doing in 2023.

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The heart of the world

One of the biggest mysteries in science lies literally beneath our feet; the structure and composition of the interior of the Earth.

We have direct access only to the barest fraction of it.  The deepest borehole ever created is the Kola Superdeep Borehole, on the Kola Peninsula in Russia near the border of Norway.  It's 12.26 kilometers deep, which is pretty impressive, but when you realize that the mean radius of the Earth is just under 6,400 kilometers, it kind of puts things in perspective.

What we know is that the crust is principally silicate rock -- lower-density felsic rocks (like granite) forming the majority of the continental crust, and denser mafic rocks (like basalt) comprising the thinner oceanic crust.  Beneath that is the semisolid mantle, which makes up two-thirds of the Earth's mass.  Inside that is the outer core, thought (primarily from estimates of density) to be made up of liquid iron and nickel, and within that the inner core, a solid ball of red-hot iron and nickel.

At least that's what we thought.  All of this was determined through inference from evidence like the relative speed of different kinds of seismic waves; despite what Jules Verne would have you believe, no one has been to the center of the Earth (nor is likely to).  But figuring all this out is important not just from the standpoint of adding to our knowledge of the planet we live on, but in comprehending phenomena like magnetic field reversals -- something that would have obvious impacts on our own lives, and which are still poorly understood at best.

We just got another piece of the puzzle in the form of a paper last week in Nature that suggests our picture of the Earth's inner core as a homogeneous ball of solid iron and nickel may not be right.  Using data from seismic waves, scientists at the Australian National University in Canberra have concluded that the inner core itself has two layers.  The exact difference between the two isn't certain -- as I said before, we're limited by what information we can get long-distance -- but the best guess is that it's a difference in crystal structure, probably caused by the immense pressures at the center.

[Image courtesy of Drew Whitehouse, Hrvoje Tkalčić, and Thanh-Son Phạm]

In general, whenever a wave crosses a boundary from one medium to another, it refracts (changes angle); this is why a straw leaning in a glass of water looks like it's bent.  If the angle is shallow enough, some of the wave's energy can also reflect off the interface.  When that happens to seismic waves inside the Earth, those reflected waves bounce around inside the core; when they finally make it back out and are measured by scientists on the Earth's surface, features such as the energy, wavelength, and angle can provide a lot of information about the materials it passed through on its journey.

The authors write:

Earth’s inner core (IC), which accounts for less than 1% of the Earth’s volume, is a time capsule of our planet’s history.  As the IC grows, the latent heat and light elements released by the solidification process drive the convection of the liquid outer core, which, in turn, maintains the geodynamo.  Although the geomagnetic field might have preceded the IC’s birth5, detectable changes in the IC’s structures with depth could signify shifts in the geomagnetic field’s operation, which could have profoundly influenced the Earth’s evolution and its eco-system.  Therefore, probing the innermost part of the IC is critical to further disentangling the time capsule and understanding Earth’s evolution in the distant past.

The discovery of the Earth's hitherto-unknown center could help us to understand one of the most fundamental questions in geology; the structure of the inside of the Earth.  We still have a very long way to go, of course.  As I said, even understanding how exactly the core generates the Earth's protective magnetic field is far from achieved.  But the new research gives us a deeper comprehension of the structure of the inner core -- the red-hot heart hidden beneath the deceptively tranquil surface of our home planet. 

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Reversing the core

I get really frustrated with science news reporting sometimes.

I mean, on the one hand, it's better that laypeople get exposed to science somehow, instead of the usual fare of the mainstream media, which is mostly stories about seriously depressing political stuff and the latest antics of celebrities.  But there's a problem with science reporting, and it's the combination of a lack of depth in understanding by the reporters, and a more deliberate desire to create clickbaity headlines and suck people in.

Take, for example, the perfectly legitimate (although not universally accepted) piece of research that appeared on January 23 in Nature Geoscience, suggesting that the Earth's inner core oscillates in its rotational speed with respect to the rest of the planet -- first going a little faster, then slowing a bit until its rotational rate matches Earth's angular velocity, then slowing further so the rest of the planet for a time outruns the core.  Then it speeds up, and does the whole thing in reverse.  The reason -- again, if it actually happens, which is still a matter of discussion amongst the experts -- is that the speed-up/slowdown occurs because of a combination of friction with the outer core, the effects of the magnetic field, and the pull of gravity from the massive mantle that lies outside it.

[Image licensed under the Creative Commons CharlesC, Earth cutaway, CC BY-SA 3.0]

That's not how this story got reported, though.  I've now seen it several times in different mainstream media, and universally, they claim that what's happening is that the inner core has stopped, and started to spin the other way -- i.e. the inner core is now rotating once a day, but in the opposite direction from the rest of the Earth.

This is flat-out impossible.  Let's start with the fact that the inner core has a mass of about 110,000,000,000,000,000,000,000 kilograms.  A mass that huge, spinning on its axis once a day, has a stupendous amount of angular momentum.  To stop the rotation of that humongous ball of nickel and iron would take an unimaginable amount of torque, and that's not even counting overcoming the drag that would be exerted by the outer core as you tried to make the inner core slow down.  (I could calculate how much, but it's just another huge number and in any case I don't feel like it, so suffice it to say it's "a shitload of torque.")  Then, to accelerate it so it's rotating at its original rate but in the opposite direction would take that much torque again.

Where's the energy coming from to do all that?

Here, the fault partly lies with the scientists; they did use the words "reversing direction" in their press release, but what they meant was "reversing direction with respect to the motion of the rest of the Earth."  I get that relative motion can be confusing to visualize -- but giving people the impression that something has stopped the inner core of the Earth and started it rotating in the opposite direction gives new meaning to "inaccurate reporting."

Worse still, I'm already seeing the woo-woos latch onto this and claim that it's a sign of the apocalypse, that the Evil Scientists™ are somehow doing this deliberately to destroy the Earth, that it's gonna make the magnetic field collapse and trigger a mass extinction, and that it's why the climate has been so bonkers lately.  (Anything but blame our rampant fossil fuel use, apparently.)  Notwithstanding that if you read the actual paper, you'll find that (1) whatever this phenomenon is, it's been going on for ages, (2) it represents a really small shift in the inner core's angular velocity, and (3) it probably won't have any major effects on we ordinary human beings.  After all, (4) the scientists have only recently figured out it's happening, and (5) not all of them believe it is happening.

So let's just all calm down a bit, okay?

In any case, I'd really appreciate it if the people reporting science stories in the mainstream media would actually read the damn papers they're reporting on.  It'd make the job of us skeptics a hell of a lot easier.  Thanks bunches.

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Flipping out

There's been a lot of buzz lately about the Earth's impending magnetic field reversal.

Well, the alleged impending magnetic field reversal.  We don't know for sure that one is imminent; it's the same sort of thing as when you hear that the Yellowstone Supervolcano is "overdue for an eruption."  Neither of these is on some kind of timetable.  You rarely hear volcanoes say, "Well, I'd love to visit, but I'm supposed to erupt at 3:34 PM today, and I can't afford to be late."

The magnetic field flip is even more irregular than supervolcano eruptions, at least to judge by the geological record.  We know reversals have happened by looking at (relatively) new igneous rock formations near the Mid-Atlantic Ridge; as the lava cools, magnetic particles in the molten rock freeze into place, locking in a magnetic signature that tells you what the Earth's magnetic field was doing at the time.  And if you do a scan across the Mid-Atlantic Ridge you find mirror-image parallel stripes along the ridge, progressively older as you move away, documenting 183 reversals over the past 83 million years.  The timing of those reversals, however -- and therefore the width of the stripes -- varies tremendously, from about 25,000 years to about ten million years (the longest stable interval discovered so far).

[Image is in the Public Domain courtesy of NOAA]

As a quick aside, you may know that these magnetic stripes were one of the most persuasive arguments for the developing theory of plate tectonics, back in the late 1950s and early 1960s.  The mid-ocean ridges were identified as divergent zones -- places where the plates were moving apart, and new rock upwelling to fill the space in between.

In any case, we don't know for sure if the Earth's field is ready to flip, but it certainly seems to be wandering around a bit.  The last full reversal was about 780,000 years ago, but there was what seems to have been an abortive flip -- the Laschamps Event -- about 41,400 years ago, which only lasted about five hundred years before flipping back to its original polarity.  (Because of the speed of the switch, geologists don't consider this to be a full geomagnetic reversal, but a "geomagnetic excursion," where the poles didn't make a long-term move but just kind of went on walkabout.)

In fact, the Laschamps Event is why the whole topic comes up.  Recently a paper was published in Science describing what scientists have learned from an unexpected source -- the sixty-ton trunk of a kauri tree (Agathis australis) that was accidentally unearthed in New Zealand by some workers breaking ground for a new power plant.  The tree trunk had been submerged in a bog and preserved, and as luck would have it, the tree's 1,700 year life span was right across the Laschamps Event.

Specifically, they looked at the content of carbon-14 in the wood; C-14 is a radioactive form of carbon that is best-known for its role in the dating of preserved organic matter, but also is a good indicator of the level of cosmic ray bombardment (because it's formed when stratospheric carbon dioxide is hit by ionizing radiation).  

What they found is a little alarming.  During the Laschamps Event the magnetic field of the Earth collapsed for something like five centuries, and the tree rings during that time show a significant spike in carbon-14 formation.  The level of bombardment, the researchers say, would have caused auroras in the subtropics -- and would have been sufficient to knock out the power grid.

Right around the same time, there were some significant biological shifts going on.  Large mammals in Australia died out, including the terrifying giant clawed wombat, Palorchestes.

In case you thought I was making this up. This thing got up to three meters from nose to tail and weighed an estimated 1,000 kilograms. [Image licensed under the Creative Commons Nobu Tamura, Palorchestes BW, CC BY 3.0]

At around the same time, Neanderthals disappeared from Europe, and things got a good bit colder -- our ancestors started taking up residence in caves, to judge by the appearance of sophisticated cave art.  Whether any or all of this is connected to the Laschamps Event, however, is unknown.

What seems certain is that if it were to occur today, it would be bad news for technology.  Not only would the flip wreak havoc on our power grid, it would foul up a lot of navigational systems.  (I wonder how birds would be affected, since many of them rely on magnetic field lines to guide their migration twice a year.)

As with all of these sorts of things, there are some people who are Chicken-Littling about the pole reversal spelling the death of humanity, and others who are shrugging and saying we'll be fine because this has happened many times in Earth's history, and here we are.  Well, yeah, giant meteor strikes and flood basalt events and ice ages have also happened many times in Earth's history, but that doesn't mean they're a good thing.

My own response is that we shouldn't panic, but we should try to prepare for it if and when it happens, i.e., listen to the damn scientists.  Which I've said about a million times before, mostly in connection to climate change and the COVID-19 vaccine, but it seems like good advice in general.

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Mathematics tends to sort people into two categories -- those who revel in it and those who detest it.  I lucked out in college to have a phenomenal calculus teacher who instilled in me a love for math that I still have today, and even though I'm far from an expert mathematician, I truly enjoy considering some of the abstruse corners of the theory of numbers.

One of the weirdest of all of the mathematical discoveries is Euler's Equation, which links five of the most important and well-known numbers -- π (the ratio between a circle's circumference and its diameter), e (the root of the natural logarithms), i (the square root of -1, and the foundation of the theory of imaginary and complex numbers), 1, and 0.  

They're related as follows:

Figuring this out took a genius like Leonhard Euler to figure out, and its implications are profound.  Nobel-Prize-winning physicist Richard Feynman called it "the most remarkable formula in mathematics;" nineteenth-century Harvard University professor of mathematics Benjamin Peirce said about Euler's Equation, "it is absolutely paradoxical; we cannot understand it, and we don't know what it means, but we have proved it, and therefore we know it must be the truth."

Since Peirce's time mathematicians have gone a long way into probing the depths of this bizarre equation, and that voyage is the subject of David Stipp's wonderful book A Most Elegant Equation: Euler's Formula and the Beauty of Mathematics.  It's fascinating reading for anyone who, like me, is intrigued by the odd properties of numbers, and Stipp has made the intricacies of Euler's Equation accessible to the layperson.  When I first learned about this strange relationship between five well-known numbers when I was in calculus class, my first reaction was, "How the hell can that be true?"  If you'd like the answer to that question -- and a lot of others along the way -- you'll love Stipp's book.

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