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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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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