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Following A Wandering North Pole
The location of the magnetic North Pole is moving toward Siberia at about 40 miles per year — and every few hundred thousand years, the North and South poles switch positions entirely. Geophysicist Ronald Merrill explains what's known about the inner workings of the Earth's magnetic field.
IRA FLATOW, host:
You're listening to SCIENCE FRIDAY. I'm Ira Flatow.
You know those numbers on the runways at airports? Ever wonder what they mean? You know, like there's a Runway 18. You see them as you taxi around. Well, besides that being a runway number, that number represents the direction of the runway.
If you just add a zero to that 18, you get 180. You know what direction the runway is pointing in: 180 is south. Of course, so you're heading south on the runway, 180 degrees from magnetic north.
Well, earlier this month - it was interesting, an airport in Tampa had to close its main runway to renumber the directional sign on it. It had to change the number on the runway, and the reason was because the position of magnetic north is moving.
And so the compass heading onboard aircraft were not matching up with the headings on the signs anymore. In fact, the magnetic pole is moving toward Siberia at about 40 miles per year. Why? How?
Joining me now to talk about the Earth's magnetic field is Ronald Merrill. He is a professor emeritus in the Department of Earth and Space Sciences at the University of Washington in Seattle and author of the book "Our Magnetic Earth," published by University of Chicago Press. Welcome to SCIENCE FRIDAY.
Professor RONALD MERRILL (Department of Earth and Space Sciences, University of Washington; Author): Thank you.
FLATOW: Things are moving that fast that they have to shut down runways now to repaint the signs?
Prof. MERRILL: Yeah, the magnetic field is constantly changing on the surface of the Earth. And in fact, it may surprise you and your listeners that the North Magnetic Pole, where the field is vertical, is not 180 degrees opposite to the South Magnetic Pole.
The North Magnetic Pole, as you mentioned, is moving very rapidly. It's now up about 85 degree latitude, while the South Magnetic Pole is only moving about three miles per year. And it's about 65 degrees latitude.
FLATOW: Are they ever going to converge someday?
Prof. MERRILL: Well, they could. To understand that, you have to understand where the origin of the magnetic field is, and that's deep inside Earth, in our core, which is iron-rich, and it's so hot there that you can't even have permanent magnetization.
In fact, the outer part of the core is so hot, it's liquid. And this liquid iron is moving about, it's boiling, much like you see in a pan of water. And just as you would, in a hydroelectric plant, convert the flow of water to make electricity, this moving iron produces electric currents, and with every electric current there's a magnetic field.
And so what we see at the Earth's surface is these magnetic fields from this very complex motions in the top of our core, and the field is therefore constantly changing.
Now, it doesn't help to describe the field that way to most of us scientists. So what we say is: Look, let's pretend it's magnetic down there, even though it's not, and we describe about 75 percent of the magnetic field by a dipole, essentially a bar magnet at the center of the Earth, it has two poles, and it's tilted about 10 degrees with respect to the rotation axis.
Now, that's only 75 percent. The other 25 percent is called a non-dipole field, and it has many ups and downs, and we have to add those two fields together to get the total field, your surface. That non-dipole field, on average, is moving westward at about .2 degrees per year.
FLATOW: So is that sort of floating around there?
Prof. MERRILL: Well, it's not - you can think of it as floating, in a sense, it's the magnetic field being carried along by the motions of this moving fluid.
FLATOW: Right, right, and when people - so when people say pole, and they get this mental image of a big bar magnet sticking in the center of the Earth, that's not an accurate representation of what's going on.
Prof. MERRILL: No, because it's too hot for permanent magnetization to be there. But scientists also describe it in terms of this dipole, this bar magnet.
FLATOW: Is this something we should be afraid of or fearful of, even if the poles do switch or meet?
Prof. MERRILL: Well, we have, from records in rocks, information of the Earth's magnetic field that goes back millions of years. And we now know that the magnetic field has reversed polarity - that is, our compasses would change 180 degrees, hundreds of times in the past.
The last time was 780,000 years ago. And during that reversal, which took about four or five thousand years, the intensity never went to zero. So some of the disasters that you see portrayed in TV and movies are not accurate.
FLATOW: And that brings up a question, let me go to the phones, to Kat(ph) in Ashland, Oregon. Hi, Kat.
KAT (Caller): Oh, hi, good morning. Thanks, I love your program. I had a question just about that. I was wondering: How quickly do those polarities reverse in the rock records? How quickly does that show? And if they did reverse now, how would that affect our electrical power grids? And I'll listen to the answer off the air.
FLATOW: Thank you, have a good weekend.
Prof. MERRILL: Okay, well, there's several questions there. The estimates for how long it takes for a magnetic field to reverse vary between about 1,000 years and 10,000 years. And we don't know the details of what the field does during the reversal. We know something about it but not the details.
We know that the intensity decreases. Now, the magnetic field of the Earth acts through what we call a magnetosphere, which protects Earth from the solar wind and magnetic storms that come from the sun.
So if the magnetic field intensity decreases, then we're more susceptible to magnetic storms, and these magnetic storms can affect our power grids.
FLATOW: Let's go to the phones, to Andre(ph) in Michigan. Hi, Andre.
ANDRE (Caller): Hello.
FLATOW: Hi there, go ahead.
ANDRE: My question is: Are you of the opinion that one of Earth's magnetic poles might have once been tidally locked onto the moon many billions of years ago, when the Earth and the moon were forming?
Prof. MERRILL: No, I don't think any mainstream geoscientists would agree with that. Certainly the moon was much closer to the Earth, and it certainly had tidal effects. Those tidal effects would affect the - or could affect some of the convention, the movement of the iron in the Earth's core, but there's no locking, like gravity. Now, the gravity is a different matter.
FLATOW: Different thing. We talked about the Tampa airport. One article about the airports quoted an FAA spokesperson as saying that not all airports would have to do this because of differences in the field from place to place. Is that correct?
Prof. MERRILL: That's correct. If I took a compass here in Seattle, it would point 20 degrees to the east of true north. If I did the same compass in Maine, it would be 20 degrees to the west. And it's because of this extra non-dipole field that it's making things very complex over the surface of the Earth, and moreover it's changing all the time.
Sometimes it goes up in some places and down in other places. Sometimes it moves mostly to the west in some places, but there are some places it moves eastward.
FLATOW: Is there one wacky place on Earth?
Prof. MERRILL: Is there one wacky place?
FLATOW: Yeah.
Prof. MERRILL: I would say that the North Magnetic Pole seems to be moving pretty fast right now.
(Soundbite of laughter)
FLATOW: But, you know, people are going to say: Oh, this is the Bermuda Triangle. That's what causes it. It's moving around. Or this is, you know, someplace in Sedona or whatever like that. That explains the - the pole explains all of that. How do you answer those questions?
Prof. MERRILL: Not very well, actually.
(Soundbite of laughter)
Prof. MERRILL: You see them on the Internet. And people even talk about the whole Earth flipping over and waves of oceans coming across our continents and destroying us during a reversal. But no mainstream scientist believes those type of things.
FLATOW: Here's a tweet from TBoshop(ph), who says: Can a magnetic field be generated in a lab using the same principle of moving molten iron, as the Earth does, or is it theoretical?
Prof. MERRILL: Actually, the process we call is a Dynamo(ph), and that is being produced in laboratories. No model is complete. It's a very complicated thing, and even with supercomputers, we can't solve the equations today.
But there are Dynamo models, for example, in Maryland, that use liquid sodium rather than iron because it's a better conductor of electricity. There are some size issues. A large body, the magnetic field, if you turn off the motions, decays much slower. It decreases much slower in time than a small body. So they're all approximations in all these things.
FLATOW: GirlieGreenie says: I thought monopole did not exist.
Prof. MERRILL: Monopoles is a single pole, and it was first suggested by Paul Dirac, a Nobel Prize-winning physicist in a previous century, to exist. Scientists are looking for them, but nobody's ever found one.
FLATOW: I think she may have thought that you were using that in your explanation of the movement of the pole...
Prof. MERRILL: I certainly hope not.
(Soundbite of laughter)
FLATOW: Communication is tough in this business. Let's go to Sam(ph) in Cleveland. Hi, Sam.
SAM (Caller): Hi.
FLATOW: Hi there.
SAM: Hi, thanks for having me. I was actually curious as to the current theory where we have so much heat in the core of the Earth, and - yeah. How can it be possible that we have a generated magnetic field, when in the schools and universities it's taught that generated heat actually disorganizes magnetic fields? And I'll take my answer off the air. Thank you.
FLATOW: Okay. Thanks.
Prof. MERRILL: Okay. The heat that you're talking about that is for something like iron or a mineral called magnetite, which is common in rock. If we heat up those minerals or iron, it will lose its magnetization. Iron loses it at 770 degrees Celsius, you know, 1,400 degrees Fahrenheit. And above that, it can't be magnetic. So we know therefore that in the center of the Earth, the magnetic field is not generated by something that's permanently magnetized. Instead, it's these electric currents that are being moved around by the iron-rich liquid.
FLATOW: Why such a difference in movement of the North and the South Magnetic Poles? Why is the north moving so much faster than the south?
Prof. MERRILL: Well, it's like - we look at the North Pole and the South Pole as special spots because the magnetic field is vertical. But if we look at the Earth as a whole, we find that some places are moving fast -changing fast, and some places are changing slowly. They're just not -don't happen to be vertical. So there's always going to be some places that are moving faster than others. The details of why any particular spot is moving is tied up in theoretical calculations that are different for different investigators. So we really do not know precisely why one spot in the Earth is moving faster than the other.
FLATOW: Mm-hmm.
Prof. MERRILL: It might be interesting, though...
FLATOW: Yeah.
Prof. MERRILL: ...to know that that north magnetic pole was actually traveling southward between 1800 and 1850. It then turned around and started going northward. And as you mentioned, Ira, it is accelerating to the north today.
FLATOW: It's accelerating?
Prof. MERRILL: Yeah. It's been going faster. In fact, at the turn of the century, it was going about 30 miles a year. Now, it's about, as you mentioned, about 40 miles a year.
FLATOW: Wow. I didn't realize that. I thought maybe it was just this constant velocity (unintelligible).
Prof. MERRILL: But it may slow down...
FLATOW: Yeah.
Prof. MERRILL: ...in the next 10 years, and go in an entirely different direction. We don't know.
FLATOW: You know, we keep hearing that some insect and animals navigate by magnetism - birds fly. Maybe bees use it. They'll use the sun, too. Does that affect their navigation, the movement of the pole, the magnetic pole?
Prof. MERRILL: The - you're correct. Animals - all the way from bacteria, up to some primates - can sense the magnetic field.
FLATOW: Mm-hmm.
Prof. MERRILL: And many animals, like many species of birds, actually use it in navigation, and so do fish, as well turtles and so on.
FLATOW: Right.
Prof. MERRILL: The field is changing slow enough that it probably doesn't have a major effect. If we were all of a sudden were to have a reversal of the field very sudden, then that would be an issue. But we don't think reversals occur that rapidly. And when geologists look into the rock record, we find that no species goes extinct for - we don't expect a species will go extinct when a magnetic field reversal occurs.
FLATOW: Mm-hmm. Talking about the moving magnetic pole this hour on SCIENCE FRIDAY, from NPR. I'm Ira Flatow, with Ronald Merrill from the University of Washington in Seattle.
So what is there yet that you would like to know if you had an unlimited check - to write a check to find out something about the magnetic poles, the fields? What do you need to know? What would you like to know that you don't know now?
Prof. MERRILL: For me?
FLATOW: Yeah.
Prof. MERRILL: Oh, I would like to know precisely the origin of the magnetic field, because we're still uncertain on that. I would like to know some of the questions that you've asked. What is causing this change in the magnetic field over time, what we call geomagnetic secular variation? I would like to know a lot more about planetary magnetic fields, and magnetic fields that exist outside of our solar system. For example, there are some objects called minute(ph) powers that have magnetic fields that are a million, billion times the size of Earth's magnetic field. And these - size of these minute powers are only a diameter of, say, 20 kilometers. How would that happen? How can they produce those strong magnetic fields?
FLATOW: Hm. Does our moon have a magnetic field?
Prof. MERRILL: It has a very weak magnetic field due to magnetization in rocks at the lunar surface. We think it may have had a dynamo, like Earth, back over four billion years ago to have produce the magnetic field that magnetized these rocks.
FLATOW: Mm-hmm.
Prof. MERRILL: But we don't know.
FLATOW: So it was not - those rocks did not come from a time when it was still part of the Earth?
Prof. MERRILL: No. In fact, the moon never - wasn't really part of the Earth. We think that there was a Mars-sized object that collided with a polaritz(ph) and spun off a lot of debris. And then the moon, created from this debris, and the Earth simultaneously in the same orbit(ph). But the idea is that the moon came from the Earth itself was an old theory...
FLATOW: Yeah.
Prof. MERRILL: ...by a fellow by the name of George Darwin, who was the son of Charles Darwin, but is no longer accepted in science.
FLATOW: Mm-hmm. What - do you have any idea what's the next airport that might have to change its runway markings?
(Soundbite of laughter)
Prof. MERRILL: I have no idea whatsoever.
(Soundbite of laughter)
Prof. MERRILL: In fact, until I read the news report, I didn't even know that Tampa International Airport was changing theirs.
(Soundbite of laughter)
FLATOW: Well, I guess, anything near Tampa would have to, right? I mean, Sarasota, maybe, something like that? If Tampa is going to do it, they're not that far away. Miami?
Prof. MERRILL: I - that's something you have to ask federal regulators.
(Soundbite of laughter)
Prof. MERRILL: I have no idea. But, I mean, obviously, you want to have correct compass information, even though I think other navigation tools like GPS are the primary navigation tools.
FLATOW: Yeah. Well, pilots always know that they have to check their magnetic deviation when they look on their charts and things - their maps and charts, whatever.
Prof. MERRILL: Yeah. And they all...
FLATOW: Because it's moving all the time, and they have to write new maps.
Prof. MERRILL: And they have compasses on all the major airlines.
FLATOW: Yeah. So it's an important thing. And I'm glad you've taken the mythology out of it and given us some fascinating things to talk about. Thank you very much, Dr. Merrill, for being part of SCIENCE FRIDAY today.
Prof. MERRILL: It's my pleasure. Thank you.
FLATOW: There you go. Ronald Merrill, professor emeritus in the Department of Earth and Space Sciences at the University of Washington in Seattle. And you want to know more about the Earth, our magnetic Earth, he's written a book, "Our Magnetic Earth," published last year by University of Chicago Press.
We're going to take a break. When we talk - when we come back, we're going to talk about another pole - kind of electrical thing. This is our electrical grid, not the magnetic field, but the electric grid that, you know, that supplies our power. It's getting more rickety by the year. What would it take to engineer a new smart grid?
We'll talk about that when we get back. So stay with us. We'll be right back after this break.
(Soundbite of music)
FLATOW: I'm Ira Flatow, and this is SCIENCE FRIDAY, from NPR.
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