Everything Everywhere Daily: History, Science, Geography & More - Earth’s Magnetic Pole Reversals (Encore)

Starting point is 00:00:00 The following is an encore presentation of Everything Everywhere Daily. Once every 450,000 years or so, the Earth undergoes a radical transformation. The planet's magnetic field will literally flip. The North Pole becomes the South Pole and vice versa. Despite the fact that we know this has happened many times in the Earth's history, we really don't know what would happen if the poles were to reverse today. Learn more about when the Earth's magnetic poles reverse on this episode of Everything Everywhere Daily. If your perceptions about the past were wrong.

Starting point is 00:00:49 ThruLine is a podcast that takes you back in time to uncover the parts of the story that may have gone unnoticed. It effectively turned day into night. And how it shaped the world now. Time travel with us every week on the Thulein podcast from NPR. Before I get into the details of how and why the Earth's magnetic poles will reverse, it's important to understand how geologists know that the Earth's magnetic poles have reversed in the past. Many rocks are made up of magnetic minerals, usually magnetite or the more weakly magnetic hematite, both of which are based on iron. When a rock first forms from

Starting point is 00:01:31 liquid magma, the individual magnetic molecules will align themselves with the Earth's magnetic field. As the rock solidifies and cools, the individual mineral molecules are then locked into place with this particular magnetic orientation. In the late 19th and early 20th centuries, geologists began to notice that some rocks were magnetized opposite to the Earth's magnetic field. The first person to notice this was a French geologist by the name of Bernard Bruin. In the 1920s, the Japanese geologist Montanori Maruyama suggested that the cause of the oppositely orientated rocks was due to the Earth's magnetic poles having been reversed. While Mariyama and Brune suspected that the Earth's poles had switched, they didn't know when it happened or how many times it had happened. The

Starting point is 00:02:15 best guess was that it happened millions of years ago. In the 50s and 60s, however, there were two developments that helped solve this puzzle. The first of which was the development of radiometric techniques for dating rocks, which I covered in a previous episode. With these techniques, it became possible to date when most rocks were formed to a reasonable degree of accuracy. The second development was the magnetic mapping of the seafloor. This was the real breakthrough. What was discovered is that on the seafloor on either side of a mid-ocean rift are parallel and symmetric bands where the magnetic orientation of the rock would be one way and then another. For example, on the mid-Atlantic rift, which runs the entire length of the Atlantic Ocean,

Starting point is 00:02:57 immediately on either side of the rift, the rocks are aligned with the current magnetic field of the earth. Then, just beyond that, there's a stripe of rocks that are magnetized the other way. And then there is another stripe beyond that, etc., etc. The width of each strip is the same on either side of the rift. The reason for this is that the rift is where the tectonic plates are slowly pulling apart from each other. Liquid magma from deep in the earth comes up in the rift and then cools to form new seafloor. As this rock solidifies, the magnetic minerals inside the rock orientate themselves to the earth's magnetic field.

Starting point is 00:03:33 This process is continuous, and over millions of years, as the plate keeps moving apart, rock gets further and further away from the rift as new rock keeps forming. The magnetic stripes on the seafloor are the frozen magnetic record of what the Earth's magnetic field was like when the rocks were first formed. The current estimate is that there have been 183 magnetic pole reversals that have taken place over the last 83 million years, and that means that they occur on average once every 450,000 years. As the Earth is much older than 83 million years, there have been many.

Starting point is 00:04:07 many more pole reversals than just 183. However, we don't have the evidence to identify them. While the average amount of time between pole reversals is 450,000 years, that doesn't mean that there's some sort of geomagnetic clock inside the Earth that flips the poles on some sort of schedule. It's believed to be a fundamentally random event. There is evidence of some pole reversals taking over 10 million years, and some which occurred after only a few centuries. In addition to permanent long-term changes in the Earth's magnetic field. There are also short-term changes that have been identified known as geomagnetic excursions. Geomagnetic excursions only last for a few thousand years and are associated with a weakening of the Earth's magnetic field by up to 20%,

Starting point is 00:04:51 and a significant change in the location of the magnetic poles by up to 45 degrees. Due to the brief geologic timescales that geomagnetic excursions occur, they're difficult to track in the deep past. However, since the last major magnetic reversal, which occurred 780,000 years ago, there are believed to have been 12 geomagnetic excursions that have taken place, the most recent, having occurred about 42,000 years ago. So, if we have evidence that the Earth's magnetic poles have reversed, why does this happen? It has to do with the outer core of the Earth,

Starting point is 00:05:25 which is a liquid consisting mainly of iron and nickel, both of which are magnetic. The movement of the liquid due to convection creates a dynamo which creates electric currents, and hence a magnetic field. Fluid dynamics are inherently complex, so complex that when Albert Einstein's son Hans told his father he wanted to go into hydraulic engineering, he supposedly told him not to because it was too difficult. There have been computer simulations of the Earth's core, which have been run for tens of thousands of simulated years, and the simulations have produced field reversals.

Starting point is 00:05:59 And likewise, experiments have been run with liquid metals, and they too have shown random reversals in magnetic polarity. Basically, a liquid dynamo producing a magnetic field is much more unstable than a simple bar magnet that we might be used to. Others have theorized that pole reversals are not spontaneous events at all, but rather they're caused by something which disrupts the liquid in the core. This could be anything from deep subduction of tectonic plates to a large meteor impact on the surface. While the evidence for magnetic pole reversals is very strong, there are still some questions that remain. The biggest one is, how long does it take for the poles to switch? There are some estimates that claim a reversal takes as long as 1,000 to 10,000 years. And there are other estimates that claim a reversal can be completed in as little as a few decades.

Starting point is 00:06:47 For all we know, both of these might be possible. The fact is, we really don't know because modern humans have never experienced a pole reversal before. The other really big question is what it would be like to live through a pole reversal and how it would affect life on Earth. The Earth's magnetic field is what protects the planet from the solar wind and most cosmic rays. As these high-energy particles approach the Earth, they're deflected by the magnetic field, protecting the planet from radiation. There are some who argue that because there have been so many pole reversals throughout history, the impact of the Earth's biosphere can't possibly be that great. The major extinction events in Earth's history don't align with magnetic pole reversals. However, you will see some people who make the exact opposite argument.

Starting point is 00:07:32 In particular, the demise of the Neanderthals coincided with the last geomagnetic excursions about 42,000 years ago. However, there hasn't been 183 mass extinction events in the last 83 million years, so at best, such events could only align with a few pole reversals. Moreover, even if the last geomagnetic excursion had something to do with the extinction of the Neanderthals, it clearly didn't wipe out humans. We do know that the process of a pull reversal would certainly cause disruptions. For starters, many animals, in particular birds, rely on the magnetic field of the Earth to navigate when they migrate.

Starting point is 00:08:10 We aren't sure how this would affect them or how quickly they could adapt. If the magnetic field was weakened substantially, it could potentially be devastating to the ozone layer. If the ozone layer were weakened, it would result in a significant increase in ultraviolet rays reaching the surface of the planet. A weakening of the Earth's magnetic field would also cause havoc with electronics in something like a wide-scale Carrington event, which I covered in a previous episode. Many satellites, which are also protected by the Earth's magnetic field, would also be rendered inoperable.

Starting point is 00:08:41 Some geologists have also speculated that after a pole reversal takes place, it could result in increased volcanism across the planet. The really big question is when the next magnetic pole reversal will happen. It certainly will happen, but we have no clue when it will happen. You will find people saying that because it happens on average every 450,000 years, and because it's been 780,000 years since the last one, we're due. However, that's basically the gambler's fallacy in action. We aren't due for a pull reversal any more than a roulette wheel is due to land on red

Starting point is 00:09:16 after it landed on green three times in a row. That being said, there are things happening with the Earth's magnetic field right now. Since the invention of the magnetometer, which could measure magnetic fields in the 1830s, the strength of the Earth's magnetic field has decreased by about 10%. In particular, there has been a large reduction in the strength of the magnetic field in an area known as the South Atlantic anomaly, which I have covered in a previous episode. And finally, the magnetic poles have been wandering at a dramatic rate. The magnetic North Pole now moves at a speed of about 55 kilometers per year. So something is definitely happening. But due to the chaotic nature of the magnetic dynamo in the core, it's impossible to tell if this is part of a geomagnetic excursion, the prelude to a full

Starting point is 00:10:05 pole reversal, or just part of the natural fluctuations of the Earth's magnetic field. Ultimately, whatever happens, whenever it happens, how it affects the planet will depend on how long it takes and how weak the magnetic field gets during the transition. A magnetic pole reversal isn't something I would stay up at night worrying about. The Earth has been through this many times before, and even if we are in the middle of something right now, it will take decades, if not millennia, to fully play out. The executive producer of Everything Everywhere Daily is Charles Daniel. The associate producers are Austin Oakden and Cameron Kiefer.

Starting point is 00:10:45 I want to thank everyone who supports the show over on Patreon. your support helps make this podcast possible. I'd also like to thank all the members of the Everything Everywhere community who are active on the Facebook group and the Discord server. If you'd like to join in the discussion, there are links to both in the show notes. And as always, if you leave a review or send me a boostagram, you two can have it read on the show.

Everything Everywhere Daily: History, Science, Geography & More - Earth’s Magnetic Pole Reversals (Encore)

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