Clay magnets

One of the most wonderful things about science is the role creativity has in discovery.  Problems that have been considered somewhere between difficult and intractable have often been solved by someone who has a sudden creative insight -- how to bring together two previously disparate bodies of knowledge, or using a technique from one realm to study an entirely different one.

Take, for example, the study that was sent my way by a reader of Skeptophilia a couple of days ago.  It has to do with the technique of paleomagnetism -- the "geological clock" provided by the fact that the Earth's magnetic field flips, for (thus far) reasons unknown.  You're probably familiar with the most famous use of paleomagnetism; it was the technique that finally cinched down the plate tectonic model as accounting for continental drift.  When magma solidifies into solid rock, tiny ferromagnetic particles that were once free to move become locked into place.  When the rock was liquid, those particles could swivel around and line up with the magnetic field of the Earth at the time; once solid, that magnetic signature was frozen in place.  When geologists doing magnetometer readings of the ocean floor on either side of the Mid-Atlantic Rift Zone found parallel stripes of rocks with the same magnetic signature, and the rock as they neared the ridge had progressively younger radioisotope ages, they knew that there was only one explanation.  New rock was welling up at the ridge from deep in the mantle, and that was pushing the plates apart, creating strips of new ocean floor all along the ridge.

[Image is in the Public Domain courtesy of the USGS]

Now, a new study has applied paleomagnetic techniques to a completely different problem.  A team at Tel Aviv University and the Hebrew University of Jerusalem has looked at the magnetic signature left in fired clay bricks -- and used it to date archaeological strata in order to pinpoint the dates of famous battles described in the Biblical Books of Kings.

Clay retains a fossilized magnetic imprint for the same reason that magma does; when the clay is plastic, the particles are free to move, but once it's fired, they're stuck in place.  What's coolest about this study, though, is how sensitive the technique has become.  Back in the 1950s, when Fred Vine and Drummond Matthews used paleomagnetism to study the sea floor, it was pretty crude.  The best they could do was say that a particular sample of rock had a magnetic field like the one we have today (shown in white on the above image) or one that was reversed with comparison to the current orientation (shown in various shades of orange).  This wouldn't be much help in archaeological settings, as the last complete polar reversal was 780,000 years ago.  Now, the technique has improved to the point that the scientists can detect tiny fluctuations not only in direction but in strength -- and that has allowed them to date strata with an accuracy of ten to fifteen years.

This has allowed the team to pinpoint firm dates of offensives against the Kingdom of Judah by Shoshenq I of Egypt (1 Kings 14: 25-26), Hazael of Damascus (2 Kings 12:18), Tiglath-Pileser III (2 Kings 15:29) and Sennacherib (2 Kings 18-19) of Assyria, and Nebuchadnezzar II of Babylon (2 Kings 25:1-21).  And while some of the findings confirmed previous dates for sites, the more accurate technique has disproven other conjectures.  For example, the site of Tel Beit She'an, thought to have been razed by Hazael of Damascus, showed a paleomagnetic date between seventy and a hundred years earlier, meaning it had fallen not to Hazael but to the campaign of Shoshenq of Egypt.

It's not only the fineness of the technique I find impressive, but the fact that the team thought of using it at all.  Creativity hinges on divergent thinking -- the ability to see multiple solutions to a problem, and to apply out-of-the-box techniques in order to find those solutions.  This is an excellent example of just that -- using a technique first pioneered in studies of plate tectonics to establish a timeline of biblical archaeology more accurate than anything we've had.

Makes you wonder what crossovers scientists will come up with next.

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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.

[Note: if you purchase this book using the image/link below, part of the proceeds goes to support Skeptophilia!]