If we look back into the geologic record of the Earth, it appears that our planet’s magnetic field flips polarity every few hundred thousand years or so. Why does this happen? When’s it supposed to happen next? Is it dangerous?
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Pamela: Hi, everyone. This is Pamela and I am here to talk to you, once again, about my favorite sponsor of our show and this is BarkBox. We’ve been super-lucky to only get sponsors who are companies that we really love – and I love BarkBox because my dog loves BarkBox. For an extra free month of BarkBox, visit barkbox.com/astro and you’ll get your free month when you subscribe to a six- or twelve-month plan – I have a twelve-month plan.
Each month, I get a new box that has a few different treats that are all natural, they’re made here in the States and Canada, there’s a couple of toys; and it’s a different theme each month and I never quite know what we’re gonna get in to. So, there was the school box month, where there was a pencil. And then there was the Thanksgiving box, which included a carrot that is my dog’s favorite toy. There’s usually a couple of different toys but only one of them becomes his favorite toy.
And the other great thing about getting these every month is it’s my personal reminder to go out, pick up all the rest of the toys that have been scattered in the house, in the yard, and throw them in the washing machine. And he has new dog toys to play with, while everything tumbles and dries.
So, go get your dog a BarkBox. They have them set up for all different sizes; pick if you have large, medium, small. They even have programs for the destructor dog. So, get yourself a happy dog. Subscribe to BarkBox. Go to barkbox.com/astro. Your dog will love you and, you know – my dog will love you anyways. Thanks.
Fraser: Astronomy Cast Episode 442: Magnetic Pole Reversal
Welcome to Astronomy Cast, our weekly facts-based journey through the cosmos, where we help you understand not only what we know but how we know what we know.
My name is Fraser Cain. I’m the publisher of Universe Today and with me is Dr. Pamela Gay, the director of Technology and Citizen Science at the Astronomical Society of the Pacific and the director of CosmoQuest.
Hey, Pamela. How are you doin’?
Pamela: I’m doin’ well. How are you doing?
Just a big reminder to everybody – of course, the eclipse 2017, August this year – if you’re planning on attending, there’s a really cool project that you’re gonna want to get involved in called the Eclipse Megamovie and it’s sort of a collaboration from the Astronomical Society of the Pacific and Google and Berkeley, I think. And they’re gonna have amateur and professional photographers across the United States – across the eclipse line – gather together and take a bunch of pictures and then merge those pictures together into one megamovie that shows the whole eclipse. So, I’m going to be doing that –
Pamela: And there’s a lot of cool science that can come out of this, from – Basically, depending on where you are, you can see how the light is getting refracted, based on – do you see Baily’s Beads? Do you see what are the nuances of how you experience the eclipse? And we’re going to be able to catch that and do that science.
Fraser: So, if you’re planning on seeing the eclipse – not necessarily with us but anywhere across the US when it happens – and you think you’ve got the right gear – like a DSLR and a reasonable lens – then do a search for “Eclipse Megamovie” and you should be able to find the project and sign up.
Alright. So, if you look back into the geologic record of the Earth. It appears that our planet’s magnetic field flips polarity every few hundred thousand years or so. Why does this happen? When’s it supposed to happen next? Is it dangerous?
Alright, Pamela, set the stage: Earth magnetic field – let’s start there. The Earth is a big magnet?
Pamela: Sort of.
So, magnetic fields are generated by lots of different things. And one of the easiest things to make a magnet out of is flowing current. This is an electromagnet. We’ve probably all done this, at some point, in school; where you take wire, you wind it around your fingers, you run electricity through it and suddenly you can fling paperclips at one another. This is what you do with electricity in middle school.
Now, with the Earth, we –
Fraser: You build an electromagnetic rail gun.
Pamela: Exactly, exactly.
Fraser: Yeah, okay. Yeah, yeah.
Pamela: This is the purpose of science class in middle school – to build weapons.
Fraser: Sure, of course.
Pamela: So, our Earth doesn’t exactly have wires attached to a battery, but what we do have is molten metal. And molten metal has lots of readily flowing electrons – that’s a fancy way of saying “current” – and, thanks to convection, this molten metal is looping through the interior of the planet. And this process is, we believe, generating our Earth’s magnetic field.
Now, for reasons that we don’t fully understand – at a rate we don’t fully understand – the magnetic field of the Earth turns itself inside out and realigns, so that what was once north becomes south, what was once south becomes north; the land stays put but the magnetic field lines reverse, so that your compass is now pointing in a different direction.
Fraser: Okay, you went straight to the reversal. That’s fine. That’s fine. Go ahead, jump forward. Spoiler alert!
But, okay – so, it’s the moving molten metal at the core of the Earth that is generating this magnetic field and aligning with, essentially, the rotation of the planet – but not quite.
Pamela: It’s the convective motion of this circulating –
Fraser: Molten metal.
Fraser: Yeah. So – and, of course, they don’t line up, right? The point where the Earth’s actually rotating and the point where the magnetic north pole is are actually in two different locations and, in fact, here in Canada, we track – we own the pole, the magnetic north pole, here in Canada – and we track its position and it’s moving.
Pamela: It is.
Pamela: And what’s amazing is, while over the course of our lifetime, we’ve been able to see it move several degrees across land, there have been points in history where looking at how the magnetic fields trapped in lava rock has recorded that changing magnetic field; it looks like, at some points in time, it was moving as fast as 6 degrees per day.
Pamela: Yeah, yeah.
Fraser: Now, we haven’t been around for a long time and we definitely haven’t had the ability to measure the event – you know, the magnetic field of the Earth. So, how do we measure, how do we know, the strength and location and position and polarity of the magnetic field into history – millions of years ago?
Pamela: Well, it actually is fossilized. In fact, it’s fossilized more readily than critters are fossilized. And this is because the minerals that come out when volcanoes erupt, when the world parts and new land is created at the mid-ocean rift, that lava has magnetic particles in it that will align with the Earth’s magnetic field and, as the lava cools and becomes rock, it freezes in that alignment.
Fraser: Oh, that is so cool! That’s amazing. So, you’ve got this fresh lava that’s coming out of the Earth. It’s got little, tiny iron filings, little magnetic particles, in –
Fraser: – you know, that are forming – I mean, rock forms crystals, right? Metal forms crystals. So, you’ve got these little particles inside the lava and they are lining up with the magnetic field lines of planet Earth before the lava cools. And you’ve got this record of the magnetic fields – the strength, the direction, the position – as this lava is flowing out and cooling.
That is one of the most amazing, sort of geologic discoveries that I can imagine. It’s beautiful.
Pamela: What’s super-cool is this provides a different way to see how our Earth has changed over time and to track things to different points in time. Because we see the same reversals creeping up across the entire planet and it’s the set of: Well, for this many tens of thousands of years, it was aligned in this direction; and then, for this entire million years, it was lined up in this other direction. And then – Oops! For 450 years, we’re going to point this way.
And so, just like the rings of a tree have patterns of sometimes thick, sometimes thin, but the rings themselves go all the way around the tree so that you see the same thick on either side if you take different samples. Well, it’s the same thing with the magnetic stripes of alignment across the planet.
Pamela: And so, we can look at the various places where a planet is forming new land over long periods of time and see: Well, this stripey section – this corresponds to 300,000 years ago; this stripey section corresponds to 800,000 years ago.
Fraser: And then, you check multiple lava flows on different parts of the world and they all line up, so that they are duplicate records of each other but they’re showing you from the different perspectives. So, you’re seeing, for example, the one in the South Pole is indicating the exact same thing that the North Pole is seeing, but it’s seeing it from the reverse perspective because it’s located on a different part of the Earth. It’s amazing!
Pamela: And another part of this that’s super-cool is you have the stripes getting formed and then, the land that they’re forming on is moving – it’s that whole continental drift thing that we talked about in the last episode.
Pamela: And we can see, essentially, the stripes drift off and rotate.
Pamela: And we can put back together what things looked like, at different points in time, by lining the stripes back up.
Fraser: Right. So, not only can you get a sense – you know, this confirmation – but you can then run back through history, of the motion of the planet and see how – You know, you can tell that this thing should have been aligned – If the continents weren’t moving, then it should have been aligned this way, but because they were moving, it’s off by 5 degrees or some amount. And you can literally, then, use that to just run the – a completely independent way of tracking the motion of the continents in the past.
Again, this process of measuring the magnetic orientation of the lava is one of the most incredible things in – you know, it’s as fascinating to me as, like, spectroscopy – you know, how you can, like, blow up the lines, the chemicals, in a star and detect planets orbiting around them. It’s just this precise, amazing science.
So, volcanologists, geologists – kudos; you are amazing.
Pamela: Well, it took them a while to get there because this is one of those discoveries that, when it was first made, everyone was like, “Ehh.”
Pamela: “Who cares?”
Fraser: Yeah, “Ehh,” you know – “whatever.”
Pamela: It was first noted back in the 1920s, when people were starting to get in to dinosaurs – the competitor to astronomy, in terms of great sciences.
Fraser: Yeah, of course. Yeah.
Pamela: All of the rocks they were seeing from the early Pleistocene were magnetically aligned the opposite of what was experienced currently – or currently, for the 1920s. And, as people started thinking about the Earth’s magnetic field, they started noting in the ‘50s that the poles seemed to be wandering and there seemed to be tie to continental drive. And it was just sort of like, “Hmm.”
Fraser: “That’s funny.” Yeah.
Pamela: “Interesting.” Yeah.
And it was only in the ‘60s that people started to really take a look at this and look at the banding and map out these changes; and notice, basically, the fact that the Atlantic Ocean is striped with alternating magnetic fields.
The bottom of the Atlantic Ocean, which has been forming over time, is this amazing record of all of these fossilized changes. And it took, essentially, 40 years from the notice of, “Huh. Pleistocene fossils are reversed magnetic field” to 1960s, of realizing exactly what this implied.
Fraser: Right – that the magnetic field lines flip polarity on a random time scale and that this has happened many, many times in the past. And what you thought used to be the North Pole – you see this on both ends. And so, if I did literally have a compass and, one year, it’s pointing north and then, the next year, it’s now pointing south? Like, it’s just – it’s worthless now.
Pamela: Well, it’s not worthless; you just have to realign yourself.
Fraser: Just look at it backwards, that’s all.
Pamela: And that’s okay.
Pamela: Just stick a new sticker on. But the –
Fraser: Repaint the little –
Fraser: – the little blob on the front that says “North”.
Pamela: Why not? Recycle.
Pamela: But the idea that it takes just one year and it’s gonna be a nice clean sweep –
Fraser: Yeah. How long does this take?
Fraser: Alright, so let’s talk about this reversal. How long does it take for this reversal to actually happen? So, from when I’m firmly North Pole to firmly South Pole, how long does that process take?
Pamela: As long as it wants to.
Fraser: How long has this process taken in the past?
Pamela: So, this is the crazy thing is – this is a fairly random process that people have been trying to find patterns in and they’re just not really succeeding. Where there appears to be evidence that some of the reversals took less than a human lifetime; in one case, it looks like it went from north to south to north again within 450 years. But, in general, it’s a process that is thought to take – in most instances but not all instances – between 1,000 to 10,000 years.
But, like I said, there’s evidence that, at one point in time – and it’s actually evidence in your neck of the wood, lava flows in the American Northwest – where you had 6 degrees change in where the pole was each day.
Fraser: Right. And even, like – Well, we’ll get to this in a bit.
So, what is going on during that time that it is changing? Is the pole, like – now, the pole is at the 49th parallel; and now, the pole’s at the equator; and now, the pole is – Or do they just, like, realign instantly? You know?
Like, you know on the sun, you get like these magnetic field lines; they’re coming out of sun spots and then they get all tangled up and then it just snaps and they reconfigure into a new configuration and it’s back to business as usual. Is that what we see?
Pamela: Pretty much.
Fraser: Or do we actually see the pole move over to its new location?
Pamela: So, in general, we see this long-term excursion of the pole. It’s the way we refer to it: “The pole wanders” –
Fraser: The pole-wander, yeah.
Pamela: It’s not set in where it wants to be. But, with the geomagnetic reversal, it is very similar to what the sun does – where it essentially turns itself inside out; you end up with multiple field lines poking through the planet in different places. It acts like there’s multiple north and south poles at the local level, if you’re walking across the surface of the planet. And there is magnetic chaos. It’s not that there’s no magnetic field, it’s that there’s a chaotic magnetic field – and one thing that is very different from with the sun is the magnetic field appears to be weaker during the period of reversal.
So, you end up with this chaos of lower magnetic field, multiple poles, the field line’s kind of tangled up and sticking out in all different directions; and then, they settle themselves out with the pole in the opposite orientation.
Fraser: Now, as I recall, the magnetic sphere around the Earth is important.
Pamela: It is.
Pamela: It really, really is.
Fraser: Which is – You know, we always talk about going to Mars. The big problem with Mars is that there’s no magnetosphere. And so, if you go out and stand on the environment, your whole body will erupt with cancer and you’ll die. So – Okay, maybe not that quickly but it’s very –
You know, we want the magnetosphere here. Without it, we would – Life on Earth would be lethal, right? Being out on the surface of the Earth –
Fraser: – would be lethal, with the amount of radiation out there.
Pamela: And this is a weakening of the magnetic field, not a destruction of the magnetic field. And so, there are some interesting side effects: You would get solar auroras at different latitudes than you currently see them. But, while getting auroras at mid-latitudes is awesome, you still have enough magnetic field that we don’t die.
And this is stood up for in the fossil record. We can go through and we can look at various parts of the planet and go, “Over here says there was a reversal; over here says there was a reversal.” There was a reversal everywhere – and no death. Because we don’t see die-offs –
Pamela: – in fossil record that are punctuated at the same times as the magnetic field reversals.
Fraser: While we do, for example, see great die-offs when there were –
Pamela: Oh, yeah.
Fraser: – supervolcanoes; when there were Armageddon asteroids. Events like that –
Fraser: – clearly caused great die-offs. But, in this case, we know the moment – the thousand years, the hundred years, the couple of years – when this reversal time was happening and we don’t see total, catastrophic death of all life on Earth.
Pamela: So, it appears we’re safe, as long as there is a magnetic field. It’s when the magnetic field goes away that we’re toast. But, while it’s simply weak, we just get different forms of aurora.
Fraser: Okay. I mean, everyone loves auroras and I know you folks in Florida are missing out on a really big aurora – so, this will be for you.
It feels, to me, like there still would be, like, some kind of increase in radiation; like, it wouldn’t be – The thought is, you know, a nicely, well-aligned, fully operational magnetosphere is better than a chaotic, flippity-floppity magnetosphere, right? Like, we want the former, we don’t want the latter.
Pamela: There will be an increase on what particles can get through. There will be an increase on how the solar wind affects the atmosphere. But it’s not death – and the “not death” is the key part here.
Fraser: Okay. So, there ya go.
Now, when did the last one happen?
Pamela: Oh, a little over 700,000 years ago.
Fraser: 700 – And how often does it happen?
Pamela: It’s estimated, over the long and fairly random process, that about every 300,000 years.
Fraser: So, we’re due in the –
Pamela: Well –
Fraser: You know – and this is where we have to go back and reference a previous episode that we just did about how, you know, there’s no such thing as “we’re due” – but are we due?
Pamela: So, there’s process where you know it happens regularly at this interval and, just like the mailman –
Pamela: Yeah, cicadas –
Pamela: Seven-year cicadas.
Fraser: Or the sun’s polar reversal.
So, there’s certain things that have a known periodicity and, when they’re delayed – each day that you’re not seeing them – There’s each minute you’re not seeing the mailman, each day you’re not seeing the seven-year cicadas that are due that year – yes, they should be hatching imminently.
Fraser: Yeah, those cicadas are going to be popping out any day now.
Pamela: Now, this is a weird process. There’s like this period where, for like a million years, the magnetic field did absolutely nothing; followed by – zip, zip, zip – back and forth, can’t decide what it wants to do. And we don’t know why.
And we can build computer models that replicate what’s going on but it’s a sufficiently chaotic process that, while we can replicate getting a magnetic dynamo – getting the pole reversals out of this convection of the liquid iron in the Earth’s core – we can’t say, “Yes. On August 24th, three days after the solar eclipse, the Earth’s magnetic field will reverse.” We can’t do that.
Fraser: Right, right. And so, to say that we are overdue, we could be overdue forever. It may never flip again. And it may –
Pamela: We’re pretty sure –
Fraser: – flip seven times in the next thousand years.
Pamela: Yeah, yeah.
Fraser: We don’t know. But, if it was going to flip – or we thought that it might be in the process of flipping – what are some signs that we might see that it was underway or that it was before being underway? What would we see?
Pamela: So, as near as we can tell, there’s an overall weakening of the field and then you end up with this effect of basically multiple, magnetic field lines coming out through the surface, acting like: Here’s the north, here’s the south – where you have the field lines cutting through.
So, think sun spots.
Pamela: Except now, we’re trapping magnetic field in all of our little magnetic-field-detecting equipment on the surface of the planet. It’s going to be the kind of thing that sort of is like, “Huh. Magnetic field seems a little weak. Let’s keep an eye on this.” “Huh. There’s the magnetic field poking out of Siberia.”
Pamela: And, “Oh, wait. We have magnetic fields everywhere now.”
So, it’s the kind of thing that will sneak up on us.
Fraser: But isn’t one of the signs that we would theoretically see the pole wandering pretty quickly?
Pamela: Yes. So, that’s one of the things that happen in some cases. But, if it’s going to be a 10,000-year flip –
Pamela: – versus a couple-of-year flip, this is something that acts however it feels like.
Fraser: But don’t we see our pole moving pretty quickly right now?
Pamela: And this is where we have two different things that we have to worry about: One is the excursions, where it’s just simply wandering about; and the other is the, “And now I shall reverse.”
Pamela: And we don’t know –
Fraser: Which one it is.
Pamela: – until you get the – yeah.
Fraser: But we are in a period – If I recall my reporting correctly, we are in a period where our pole is moving pretty rapidly.
Pamela: It is.
Fraser: Unusually quickly. So –
Pamela: But that doesn’t mean it’s gonna reverse. It doesn’t have to; it can do what it feels like.
Fraser: It can do what it wants and, you know – it doesn’t matter to us or the compass companies.
Pamela: Magnetic field doesn’t care.
Fraser: Alright, let’s talk about consequences then.
So, let’s say – You know, we talked about the radiation and our need for a magnetosphere. Birds appear to navigate by the magnets in their heads. Would they have a problem?
Pamela: Yeah. Well, so here’s the thing. We do have the whole “no death” in the fossil record. That doesn’t mean you don’t end up with things deciding, “And I shall nest over here now because my magnetic field sent me somewhere totally different.”
With the gradual processes that we see now, generation after generation, the birds are able to figure out where they’re supposed to be. We don’t have the swans, the sparrows, the whatever birds, radically changing their nesting sites due to magnetic wander; we do have them moving because of human beings. So, looking at all the impact factors, one generation of birds to the next can figure out, “Oh! I now need to navigate slightly more to the left.”
Pamela: So, it’s – Life has a way of adapting.
Fraser: Right. So, you might have a generation of birds that’s completely confused, goes in the wrong direction and suffers.
Pamela: Finds a great new nesting site.
Fraser: Or suffers a terrible die-off.
Fraser: But then you’re gonna see a follow-up generation – you know, the ones who will evolve the correct direction – and, within a few generations, they’ll be back in business – and now they’re going to have upside-down compasses in their heads.
Pamela: And, while we may end up with some critters that struggle due to these navigation issues, there is no evidence – and I’m just going to keep saying this – there is no evidence for massive die-offs –
Pamela: – tied to magnetic field reversal. And the actual planet just keeps spinning in its normal orientation.
Fraser: Right. And so – And we can’t find evidence of confused birds, right?
Pamela: No, no – that’s probably a little too fine a grain for fossil record.
What about our technology?
Pamela: Yeah, that’s a different problem because life hasn’t been as technologically evolved at any point when there’s been a past reversal and we use magnetic fields a lot. Now, GPS satellites do help.
Pamela: But –
Fraser: So, 50 years ago, a worldwide jumbling of the magnetic field would cause total chaos to our navigation system – you know, airplanes and boats. Now they all have GPS, so we’re kind of protected, right?
Pamela: We’re a little bit better off but we use the Earth’s magnetic field to push against for a lot of spacecraft; it’s part of how they do their navigation thing. And so, you start having difficulties with how we handle spacecraft if we have a significantly weakened field that you can’t push as hard against.
I think we’re going to find that there’s a whole lot of stuff we hadn’t really thought through how much it relied on the Earth’s magnetic field –
Pamela: – if that field suddenly is a lot less intense.
So, in conclusion, the Earth’s pole flips every now and then. We don’t know why, we don’t know when it’s going to happen. We don’t know when it’s going to happen next. It’s probably alright. Don’t worry about it.
Pamela: But it will be a bad generation or so.
Fraser: Yeah. But it’s fascinating.
Fraser: Thanks, Pamela.
Pamela: My pleasure.
Male Speaker: Thank you for listening to Astronomy Cast, a non-profit resource provided by Astrosphere New Media Association, Fraser Cain and Dr. Pamela Gay. You can find show notes and transcripts for every episode at astronomycast.com. You can email us at email@example.com. Tweet us @astronomycast. Like us on Facebook or circle us on Google Plus.
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Duration: 30 minutes