First measurement of magnetic field in Earth's core

Image: NASA

Earth’s internal dynamo generates average field in outer core 50 times that at surface

A University of California, Berkeley, geophysicist has made the first-ever measurement of the strength of the magnetic field inside Earth’s core, 1,800 miles underground.

The magnetic field strength is 25 Gauss, or 50 times stronger than the magnetic field at the surface that makes compass needles align north-south. Though this number is in the middle of the range geophysicists predict, it puts constraints on the identity of the heat sources in the core that keep the internal dynamo running to maintain this magnetic field.

“This is the first really good number we’ve had based on observations, not inference,” said author Bruce A. Buffett, professor of earth and planetary science at UC Berkeley. “The result is not controversial, but it does rule out a very weak magnetic field and argues against a very strong field.”

The results are published in the Dec. 16 issue of the journal Nature.

A strong magnetic field inside the outer core means there is a lot of convection and thus a lot of heat being produced, which scientists would need to account for, Buffett said. The presumed sources of energy are the residual heat from 4 billion years ago when the planet was hot and molten, release of gravitational energy as heavy elements sink to the bottom of the liquid core, and radioactive decay of long-lived elements such as potassium, uranium and thorium.

A weak field – 5 Gauss, for example – would imply that little heat is being supplied by radioactive decay, while a strong field, on the order of 100 Gauss, would imply a large contribution from radioactive decay.

“A measurement of the magnetic field tells us what the energy requirements are and what the sources of heat are,” Buffett said.

About 60 percent of the power generated inside the earth likely comes from the exclusion of light elements from the solid inner core as it freezes and grows, he said. This constantly builds up crud in the outer core.

The Earth’s magnetic field is produced in the outer two-thirds of the planet’s iron/nickel core. This outer core, about 1,400 miles thick, is liquid, while the inner core is a frozen iron and nickel wrecking ball with a radius of about 800 miles – roughly the size of the moon. The core is surrounded by a hot, gooey mantle and a rigid surface crust.

The cooling Earth originally captured its magnetic field from the planetary disk in which the solar system formed. That field would have disappeared within 10,000 years if not for the planet’s internal dynamo, which regenerates the field thanks to heat produced inside the planet. The heat makes the liquid outer core boil, or “convect,” and as the conducting metals rise and then sink through the existing magnetic field, they create electrical currents that maintain the magnetic field. This roiling dynamo produces a slowly shifting magnetic field at the surface.

“You get changes in the surface magnetic field that look a lot like gyres and flows in the oceans and the atmosphere, but these are being driven by fluid flow in the outer core,” Buffett said.

Buffett is a theoretician who uses observations to improve computer models of the earth’s internal dynamo. Now at work on a second generation model, he admits that a lack of information about conditions in the earth’s interior has been a big hindrance to making accurate models.

He realized, however, that the tug of the moon on the tilt of the earth’s spin axis could provide information about the magnetic field inside. This tug would make the inner core precess – that is, make the spin axis slowly rotate in the opposite direction – which would produce magnetic changes in the outer core that damp the precession. Radio observations of distant quasars – extremely bright, active galaxies – provide very precise measurements of the changes in the earth’s rotation axis needed to calculate this damping.

“The moon is continually forcing the rotation axis of the core to precess, and we’re looking at the response of the fluid outer core to the precession of the inner core,” he said.

By calculating the effect of the moon on the spinning inner core, Buffett discovered that the precession makes the slightly out-of-round inner core generate shear waves in the liquid outer core. These waves of molten iron and nickel move within a tight cone only 30 to 40 meters thick, interacting with the magnetic field to produce an electric current that heats the liquid. This serves to damp the precession of the rotation axis. The damping causes the precession to lag behind the moon as it orbits the earth. A measurement of the lag allowed Buffett to calculate the magnitude of the damping and thus of the magnetic field inside the outer core.

Buffett noted that the calculated field – 25 Gauss – is an average over the entire outer core. The field is expected to vary with position.

“I still find it remarkable that we can look to distant quasars to get insights into the deep interior of our planet,” Buffett said.

###

 

The work was funded by the National Science Foundation.

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Jenn Oates

Whoooo hoooo! Structure of our planet is first out of the chute when we come back from our Christmas holiday. Perfect lead-in!

Senter

[Reply]Please repost in ‘tips and notes’. Thanks. RT-mod

ozspeaksup

what? Nature published some real science…for a change…( non climate -that is)

Very interesting!

jack morrow

Interesting indeed. I don’t quite understand how you can have a frozen inner core of iron and nickle surrounded by a molten core of iron and nickle. I’m thinking the inner core is something else besides frozen.

It is not hot in there then, as heat demagnetizes?

“I still find it remarkable that we can look to distant quasars to get insights into the deep interior of our planet,” Buffett said.
So do I! Quite amazing. but I do worry about his approach “based on observations, not inference” certainly not the mannly thing to do.

Kath

Can we get the climatologists to model this and its effects on climate 1,000 years into the future so that we can start panicking now?
Seriously, though, I would love to see how the gravitational component decays over time. Or has this ended and is the core now in the cooling phase?
TGIF

Senter

Sorry Mod, reposted in the correct topic.

CodeTech

jack morrow, it’s because of pressure. Pressure at the inner core is estimated at around 350 GPa (billion pascals), and at that pressure the primary elements of nickel and iron solidify.

First we should ask ourselves why does magnetism occur with preference with Iron, Nickel and Cobalt, that share in common having +2 and +3 valences, changing of oxidation states in between the two ( a current), specially in iron magnetite (FeO+Fe2O4=Fe3O4).
We are lacking the vision of a general law, which manifests everywhere and, however, it is not found anywhere. Curious.

Mike McMillan

Motion of a conductor through a magnetic field generates a current that has been perpetuating the magnetic field for billions of years after the original field has dissipated.
The government should do something.

JEM

“This is the first really good number we’ve had based on observations, not inference,”
A novel concept.
“You get changes in the surface magnetic field that look a lot like gyres and flows in the oceans and the atmosphere, but these are being driven by fluid flow in the outer core,”
Anybody got about eleven trillion tons of iron powder? Sounds to me like we could have one hell of a (nearly-)spherical Etch-a-Sketch here.

kuhnkat

Frozen means solid and colder than the outer liquid layer!!!

G.L. Alston

…but I do worry about his approach “based on observations, not inference” certainly not the mannly thing to do.
[groan]
Good one anyway. 🙂

paulID

what gets me is that this guy shows that as a real scientist he has a hard time making models without observations to verify them, wish climate science had those issues.

Sandy

The inner core can be frozen whilst surrounded by a hotter liquid because it is under higher pressure. Water is very unusual in that it expands on freezing, almost all other liquids can be made to ‘freeze’ by pressure so an ocean of petrol say would become solid within a few hundred feet of the surface.

OK S.

Related news from a couple of days ago from Hebrew University, via Wired:
“Iron Age Copper Reveals Earth’s Stronger, Faster Magnetic Field”
http://www.wired.com/wiredscience/2010/12/magnetic-copper-slag/

SAN FRANCISCO — Slag left over from Iron Age copper smelting shows the Earth’s magnetic field was stronger and more variable than scientists ever imagined.
“This is a very challenging result,” said geomagnetist Luis Silva of the University of Leeds, who was not involved in the new work. “It’s completely outside of anything we thought could be happening in the core.”
The Earth’s magnetic field comes from the movement of molten iron in the core. The field’s strength and structure are constantly changing. But paleomagnetists (scientists who study the history of the Earth’s magnetic field) thought the changes were usually small and slow, fluctuating by about 16 percent over the course of a century.
But a new study of ancient copper mines in southern Israel found that the strength of the magnetic field could double and then fall back down in less than 20 years.
“The magnetic field reached an intensity that was much higher than anyone had ever thought before, two and a half times the present field,” said graduate student Ron Shaar of the Hebrew University of Jerusalem, lead author of the new study. “And you can have dramatic changes in the intensity of the field in periods of less than decades.” Shaar presented his results in a poster here at the American Geophysical Union meeting Dec. 14, and in a paper to appear in Earth and Planetary Science Letters.

OK S.

Chris Reeve

Re: “The cooling Earth originally captured its magnetic field from the planetary disk in which the solar system formed.”
This is what we call “new physics.” Notice that the reporter completely fails to mention that this is a hypothesis.
Re: “That field would have disappeared within 10,000 years if not for the planet’s internal dynamo, which regenerates the field thanks to heat produced inside the planet.”
A problem created by the conventional framework itself …
Re: “The heat makes the liquid outer core boil, or “convect,” and as the conducting metals rise and then sink through the existing magnetic field, they create electrical currents that maintain the magnetic field. This roiling dynamo produces a slowly shifting magnetic field at the surface.”
Never mind the observation that we see lightning going to space now, and that each time a lightning stroke occurs, the Van Allen Radiation Belts blink.
Re: “You get changes in the surface magnetic field that look a lot like gyres and flows in the oceans and the atmosphere, but these are being driven by fluid flow in the outer core,” Buffett said.
Electrical processes are always second-order effects in the conventional theories.
Re: “Buffett is a theoretician who uses observations to improve computer models of the earth’s internal dynamo. Now at work on a second generation model, he admits that a lack of information about conditions in the earth’s interior has been a big hindrance to making accurate models.”
In science, we are supposed to be skeptical of concepts which are invisible and theoretical. Philosophy of science dictates that we — reporters included — speak in terms which are unbiased, and hold out for the possibility that our assumptions might be wrong.
One need not be a professional scientist to determine the philosophical errors here. These guys are pretending as though philosophy of science does not even exist.

Richard111

Magnetic reversals. Are we not overdue for one?
The magnetic field is weaking, or so I have read.
Would another reading in a year or so confirm the direction?

Toto

I don’t know what “philosophy of science” is. Maybe that’s like the theory of science as opposed to the practice of science. I do know what the difference between philosophy and science is. Philosophy came first. It is pure speculation, attempting to think or “reason” about things, what we would now call “hand-waving”. If you add to that better logic, mathematics and even statistics, experiments, ways to falsify claims, an attempt to separate claims from facts, then you start to have science. The problem with “climate scientists” is that many of them are at best philosophers not real scientists. They might as well be science-fiction writers or the priests of a new religion. end rant.

Helge

Diameter of earth approx 12.000 kilometers
Deepest borehole approx. 12 kilometers
So. We have ‘observed’ the composition of earth two thousands (0.2 %) of the way down towards the center. What would we be able to say about an apple or a an animal cell if we only could study a small part of the way into the peel/cell membrane ?

Toto

related story: “European scientists are going to try to measure the movement of the oceans by tracing their magnetism alone.” Swarm satellite mission.
http://www.bbc.co.uk/news/science-environment-11980315

Mike McMillan says:
December 17, 2010 at 8:12 am
A Unified Field needed.

I didn’t really intend to be this active a poster on my first day, but I find it interesting that the potential for serious effects on civilization lie in the periodic fading of the Earth’s magnetic field (we are quite overdue for the next “outage”, apparently) exceeds in some respects any of those speculated to arise from climate change. Homing pigeons, I cry for you!
http://en.wikipedia.org/wiki/Geomagnetic_reversal

Richard G

Anthony, Please check out this article on ULF radio waves detected by a French satellite over Haiti prior to the 7.0 Quake.
http://www.technologyreview.com/blog/arxiv/26114/

An interesting hypothesis, but only a hypothesis. Earth’s magnetic field has number of anomalies that the above would have difficulty in explaining.
Magnetic field in the North hemisphere behaves in totally different manner to the south. I would assume Moon would act equally on both. North hemisphere field has reversed correlation to the solar, but precedes it by about one Hale cycle, while the south is ~ logarithmic decay.
http://www.vukcevic.talktalk.net/LFC9.htm
It would be indeed strange if the Moon modulated sunspot cycle.
I have no idea what and how the Earth’s field is generated, but I am a bit sceptical of people who claim that they know. This bit of science is the long way from being settled.

DesertYote

Helge
December 17, 2010 at 9:39 am
“So. We have ‘observed’ the composition of earth two thousands (0.2 %) of the way down towards the center.”
###
Um, no. Mankind has made “observations” of the interior of the planet all the way to the core.

Tony

Chris,
That’s pretty much the norm in science reporting anymore. Try reading an article (or worse yet, watching a “Science” channel show) on String Theory.

tapper of spines

I would suggest modifying your title, Anthony.
First, this is not a measurement of the Earth’s core magnetic field. This is an inference of the Earth’s core magnetic field based on other measurements. Not the same thing. We cannot measure the Earth’s magnetic field within the core without inserting some sort of probe into it. Let me know when you figure that one out.
Second, this is not the first time that the strength of the magnetic field within the core has been inferred. It’s been done many times before, under a whole variety of assumptions. Here’s an example, again from Nature, that was published just a few months ago:
http://www.nature.com/nature/journal/v465/n7294/full/nature09010.html
TOS
REPLY: The title is the one from the press release, not mine. See http://www.berkeley.edu/news/media/releases/2010/12/16_earth_magnetic_field.shtml
-Anthony

Richard G says:
December 17, 2010 at 10:31 am
You can also know when an earthquake it is about to happen by having this Ipod App:
http://itunes.apple.com/us/app/gravity-meter/id358324984?mt=8
During an earthquake the acceleration of gravity varies. During the Feb.27 2010 8.9 degrees Richter earthquake a watchman and his wife knew it was one coming because in the school he work it has been installed an accelerator connected to a siren, so they went out 5 minutes before the earthquake. They were about to get back inside the building when it started the “fun”.
All fields are related, though current water tight compartments between branches of science and prejudices avoid the recognition of this fact. (you can also click on my link, above)

Chris Reeve

Re: “I don’t know what “philosophy of science” is. Maybe that’s like the theory of science as opposed to the practice of science. I do know what the difference between philosophy and science is. Philosophy came first. It is pure speculation, attempting to think or “reason” about things, what we would now call “hand-waving”.”
Hand-waving is what happens when there is no philosophy behind a thinker’s actions. We all intuitively understand what philosophy of science is. It’s what keeps scientists fair and objective about their research. It’s not so much a set of rules, as it is a general guide (or way of doing business) which keeps scientists from casting their own human preferences and prejudices onto their methodologies, assumptions, inferences and conclusions. Our theories are supposed to be “pure” of human likes and dislikes, as they are supposed to reflect things like data and logical arguments. A human preference can be thought of as the antithesis of philosophy of science.
Philosophy of science is most important at the point of the inferential step. All humans possess prejudices and preferences for theories, based upon our reading selection and education. But, the peer review process and the scientific method are, in theory at least, supposed to be above all of that. So, philosophy of science is all that protects our theories from our own human failings. Scientists who ignore it will tend to just ignore those inferences which they don’t like, and only consider those which they do. If you ever happen to pick up a book on philosophy of science, you will see them discuss concrete examples where this has historically occurred. Whenever you hear a scientist say, “We’ve ruled everything out except …”, this is when red flags should go off, because they assume the conventional theories to begin with for just about ALL research that goes on today. It would be more proper to state:
“Assuming the conventional framework (Lambda CDM, the Standard Solar Model, etc.), we can rule out everything but …”
Re: “If you add to that better logic, mathematics and even statistics, experiments, ways to falsify claims, an attempt to separate claims from facts, then you start to have science.”
But, without a philosophy, there is potential for abuse. For instance, if they refuse to read or listen to arguments which they disagree with, while simultaneously demanding that the burden of proof is upon those making competing claims to prove their case, they’ve just created an impossible situation for novel, competing ideas. We should all be able to agree that there exists no philosophy in this approach, as it favors one theory — the dominant one — over all others. In this particular case, philosophy of science prevents science from stagnating.
Another example is cosmic microwave background. A philosophical approach to science dictates that theorists must be willing to consider all potential inferences which are “physical” before considering those which are more “meta-physical”. So, when cosmologists saw an electromagnetic fog of microwaves coming at the Earth from all directions, they opted to infer that this was a relic of a primordial explosion which created all of time and space. However, had they stepped into a plasma laboratory and done experiments on plasma beams — which they knew at that time was the universe’s preferred state for matter — they would have also realized that plasma beams always emit microwaves. Plasmas emit spikey synchrotron instead of a smooth black body bell curve, but does it really matter? Thermalizing this synchrotron into a bell curve is not a meta-physical inference. Imagining that you’re seeing a relic of a primordial explosion which created matter, time and space certainly IS.
There are numerous examples which I could point to. The point is that, with philosophy as a guide, we can better see the larger context for how to evaluate cosmologies. Without philosophy, we are forced to compare one cosmology on the basis of another without any guide to keep us honest. And since cosmologies can present dramatically different types of evidence to begin with, this latter misinformed approach will ultimately be nothing more than an expression of our human preferences and prejudices.
Re: “The problem with “climate scientists” is that many of them are at best philosophers not real scientists. They might as well be science-fiction writers or the priests of a new religion. end rant.”
I see and agree with what you’re saying, but I would prefer to use a different word than “philosophers”. Before humans started breaking the scientific disciplines up into pieces, scientists like James Maxwell were called “natural philosophers”. It’s a great term because it reminded every one of them that scientists are bound to the philosophical thinking which happened many years ago in Greece, which has served as the fundamental basis for much of our modern-day thinking.
Modern-day climate science and even modern-day cosmology are NOT based upon this solid philosophical foundation. Astrophysicists also make a number of very serious philosophical errors in their own analysis.

David, UK

kuhnkat says:
December 17, 2010 at 8:41 am
Frozen means solid and colder than the outer liquid layer!!!

Not sure if the term “frozen” means anything more than just “solid.” As I understand it, the core is in a solid state simply due to the intensely high pressure, but is still at an extremely high temperature. Am I wrong?

James F. Evans

Toto says: “I don’t know what ‘philosophy of science’ is.”
The philosophy of science is the methodology or process of coming to a scientific understanding. It’s also called natural philosophy.
Principly, it means empirical observation & measurement of actual physical events is the road to correctly understanding those physical events.
A priori assumptions lead to errors in scientific understanding.
“CO2 is what causes warming,” is an example of an a priori assumption.

Stephen Rasey

According to this model, how does an Earth magnetic field survive hundreds of polarity reversals as well documented in the geologic column? One would think a quick dampening of the dynamo would result.
I cannot help but think there are some high-pressure, high-temperature physics going on we know little about.

jack morrow

Ok, the core is frozen iron. I guess the sun iron core theory is right too? Hmmmm.

Malcolm Miller

I used to work on Earth rotation, and remember when it wasa first suggested that distant quasars could be used as a precise indicator of irregularities in the Earth’s motion. Congratulations to the radio astronomers who devised this procedure, and to those who have used it to investigate the nature of the planet’s magnetic field.

Chris Reeve

Re: ““The magnetic field reached an intensity that was much higher than anyone had ever thought before, two and a half times the present field,” said graduate student Ron Shaar of the Hebrew University of Jerusalem, lead author of the new study. “And you can have dramatic changes in the intensity of the field in periods of less than decades.” Shaar presented his results in a poster here at the American Geophysical Union meeting Dec. 14, and in a paper to appear in Earth and Planetary Science Letters.”
It’s worth noting that within the plasma-based cosmologies, that two cosmic bodies which approach one another will eventually charge-neutralize with one another. And one has to imagine that these enormous electrical discharges will show up in the geologic record as dramatic changes in the magnetization of Earth’s rocks.
What they are seeing is arguably evidence for global catastrophe. It’s further evidence that we should be abandoning the uniformitarian view which theorists to this day still cling to. For those still taking count after all of these years, Velikovsky is actually winning some of these really old catastrophist debates.

DesertYote

Toto says:
December 17, 2010 at 9:37 am
They might as well be science-fiction writers or the priests of a new religion. end rant.
###
You are way off base here. Before you start insulting something you should at least have some idea of what you are talking about. You seem to be very ignorant of the nature of actual science-fiction; confusing it with that socialist crap praised by the lefties, written by authors who might write one pseudo SF story in their entire life (and wear ugly glasses, to boot). That’s not SF, its socialist propaganda.
Real SF is based on the extrapolation of REAL science.

Jeff (of Colorado)

Dear Anthony: I asked about this topic a number of weeks/months ago (time flies). Thank you very much for bringing up some information and discussion about it!!
It seems that the physics 12,000 miles beneath our feet is poorly understood yet is somehow intricately linked with the moon and sun. Our little home in space is built on an amazing foundation.
Merry Christmas, Happy Holidays and have a wonderful New Year! Jeff

William

The geomagnetic field is interesting as there are multiple observations which the mainstream mechanism that is hypothesized to generate the geomagnetic field, the self dynamo cannot explain.
The follow are some of the issues and links to papers for those who are interested in this subject.
The geomagnetic field protections the earth from loss of water (H2) to the solar wind. It is known that the geomagnetic field is at least 3.5 billion years old. The geomagnetic dynamo mechanism requires a specific heat source that creates a heat gradient to drive convection in the liquid core. That requires that the earth cool to create a heat gradient. The heat gradient is hypothesized to be generated by the solidifying of the core, however, basic analysis indicates the solid core is at most 1 billion years old, based on the current heat loss. That problem is called the heat flux problem or paradox as prior to the core solidifying there is no mechanism to generate a heat gradient.
http://www.sciencedaily.com/releases/2010/03/100304142236.htm
http://www.iugg.org/IAGA/iaga_pages/pdf/toulouse2005/david_loper.pdf
It has been found that the geomagnetic field changes suddenly and that the changes are cyclic. The changes correlate with climate change events. One theory is the climate change causes the geomagnetic field changes (the ice sheet changes are hypothesized to alter core motion) however the cyclic geomagnetic field changes lead rather than follows the climate change and the ice sheet changes are orders of magnitude to small to alter the core. There is currently no accepted mainstream explanation to why the geomagnetic field changes cyclically.
Recent analysis has confirmed very rapid field changes have occurred in the past which are faster than a core generated field change can produce. The mantel is slightly conductive and hence retards the fast core generating field changes from reaching the surface by generating a counter acting EMF.
There are periods of 10 millions of years called superchrons when the geomagnetic field no longer reverses. There is no explanation as to why that is so or why the period between geomagnetic field reversals has varied with geological time.
http://eprints.whiterose.ac.uk/416/1/gubbinsd4.pdf
“Is the geodynamo process intrinsically unstable?
Recent palaeomagnetic studies suggest that excursions of the geomagnetic field, during which the intensity drops suddenly by a factor of 5 to 10 and the local direction changes dramatically, are more common than previously expected. The `normal’ state of the geomagnetic field, dominated by an axial dipole, seems to be interrupted every 30 to 100 kyr; it may not therefore be as stable as we thought. We have investigated a possible mechanism for the instability of the geodynamo by calculating the critical Rayleigh number (Rc) for the onset of convection in a rotating spherical shell permeated by an imposed magnetic field with both toroidal and poloidal components.
Recent studies suggest that the Earth’s magnetic field has fallen dramatically in magnitude and changed direction repeatedly since the last reversal 700 kyr ago (Langereis et al. 1997; Lund et al. 1998). These important results paint a rather different picture of the long-term behaviour of the field from the conventional one of a steady dipole reversing at random intervals: instead, the field appears to spend up to 20 per cent of its time in a weak, non-dipole state (Lund et al. 1998). One of us (Gubbins 1999) has suggested that this is evidence of a rapid natural timescale (500 yr) in the outer core, and that the magnetic field is usually prevented from reversing completely by the longer diffusion time of the inner core (2 to 5 kyr). This raises
a number of important but difficult questions for geodynamo theory. How can the geomagnetic field change so rapidly and dramatically? Can slight variations of the geomagnetic field affect the dynamics of core convection significantly? If so, is the geodynamo process intrinsically unstable?”
http://www.osdpd.noaa.gov/data/sst/anomaly/2010/anomnight.12.16.2010.gif
http://www.ias.ac.in/currsci/apr252003/1105.pdf
“Furthermore, because the inner and outer core are electrical conductors, the magnetic field within them cannot change arbitrarily. In particular, this field can only diffuse into or out from the solid inner core relatively slowly. The characteristic time scale for the field to change significantly within the inner core is estimated5 as ~ 3 ka. To crudely summarize a very complex situation, numerical simulation indicates that the flow in the outer core is constantly trying to reverse the polarity of the field on the short (~ 100 year) characteristic time scale of its convective circulation.”
“It is indeed notable that the Laschamp, Mono Lake, and Gothenburg excursions, the three youngest, all occurred just before Heinrich events (Figure 6).
The Gothenburg excursion occurred in the early part of the Younger Dryas stage46, the brief cooling within the transition from the last glacial maximum to the Holocene. Some studies46,47 reported that the global sea level fell at this time by ~ 10 m for a few centuries before rising again as melting resumed: consistent with the observed growth of the Laurentian, Scandinavian, and Scottish ice sheets 48–52.”
http://agenda.albanova.se/getFile.py/access?resId=250&materialId=252&confId=2522
The laboratory attempts to create a self generating dynamo by convection have not been successful. (i.e. An external magnetic field is required to maintain the dynamo.)
“Early attempts to understand the dynamo action of a liquid conductor were largely
unsuccessful because only complicated fluid flows can produce the required regeneration of the magnetic field. It is now possible to model the magnetic-induction effects by supercomputer, but not the turbulence of flow in Earth’s outer core nor Earth’s rapid spin rate. Perhaps surprisingly, computer models using greatly simplified assumptions do reproduce aspects of the geomagnetic field such as the dipole, somewhat unrealistic reversals, and parts of the present non-dipole field (Fig. 6).”
“No, there are very long intervals of time, called superchrons, when there were no reversals. The last one, the Cretaceous normal superchron, was from about 124 million to 80 million years ago.”

Alchemy

A textually dense entry just above, but I think I got the gist.
An interesting idea is contemplating whether there is a relation between the rapid (in geological terms) dipole shifting of the Earth and equally rapid climate change. Also intriguing is establishing whether external forces affect the dipole shift and perhaps make such a shift a marker for climate variability.
This entry made me think of about the best science book I’ve ever read:
http://www.amazon.com/Oxygen-Molecule-that-Made-World/dp/0198508034
One of the mysteries discussed within it is how oxygen rose to an astounding 35% of the atmosphere (it’s currently about 20%) in the age of the dinosaurs. That’s enough to ensure just about every spark going would start a serious fire…and certainly led to today’s vast coal beds.
One wonders if the Creataceous “superchron” ties in in any fashion to the long slow rise of the toxic oxygen gas to levels that approached those necessary to set the very air on fire.

Larry in Texas

So, it can be said our planet’s magnetic field is a “Goldilocks” field – not too weak, not too strong, but just about right. Just right for our purposes, anyway.

Brian H

Newton’s comment about admiring pebbles on the shore of a sea of unknowns comes to mind …

cba

One shouldn’t leave out that most of the planets have magnetic fields. Earth, Jupiter, & Saturn all have fields that are close to their rotational axis, typ. around 11 deg although Earth’s seems to be moving around quite a bit these days. These three appear to have their internal bar magnet centered with the planet’s center as well as having the directions roughly coinciding. the other two planets with magnetic fields of significant size are Neptune and Uranus. It seems that their internal bar magnets (equivalence used for conceptual understanding) are located well away from being located at their planet’s centers. Also these fields do not align anywhere close to their rotational axes. Note that since Uranus has a rotational axis that is virtually parallel rather than almost perpendicular to the planetary disk, it may well have suffered some catastrophe early on that could have had an effect on its magnetic field but Neptune does not have such evidence yet is quite similar to Uranus’ magnetic field being well off center and not nearly aligned with the rotational axis of the planet.

Pascvaks

This is sooooooo incredibly frightening that I have no doubt the “Mann, Jones, Gore & Co. LLC” will use this new finding to scare the socks off Big Oil, Wall Street, the White House, London, Tokyo, and Sidney, oh yes and that EU thing. This is definitely a case of Anthroprogenicaly Induced Universal Collapse (henseforth and evermore, ta da da da, “AIUC”). I have a feeling their speech writers are going to be burning the midnight solar generators, so to speak, and Hollywood and New England Greenies are going to be wearing sackcloth and ashes like there’s no tomorrow. Mind you, THIS IS BIG!!! Once it can be statistically proven via simulations on supercomputers using two demension programs with a few odd variables that this is actually what is going to happen in a few billion years the West will simply have to surrender and go Commie and we will finally be able to start turning things around. Won’t Chairman Big Brother in Peking be proud? (SarcOff)

tapper of spines says:
December 17, 2010 at 10:56 am
We cannot measure the Earth’s magnetic field within the core without inserting some sort of probe into it.
You do not understand what a measurement is. What you are saying is akin to claiming [I’m sure some nuts would actually do that] that we cannot measure the Sun’s temperature without inserting some thermometer into it at the surface.
The magnetic field we measure at the surface is the field from the core. We are sitting in it. The field decreases with the cube of the distance. So if the field is generated [say] at a quarter of the Earth’s radius from the center, it would at the surface have decreased by a factor of 4*4*4 = 64; if at a third of a radius, the factor would be 3*3*3 = 27; if somewhere in between we would get a factor between 27 and 64, say, ~50, which is about what is observed. No mystery here. What the measurements referred to is saying is that the field is indeed generated about where we thought it would be generated. In other words, it is a really measurement of where the field is generated.

All these assumptions and calculations are misleading. It might be OK if there was a big magnet somewhere in the Earth’s interior in shape of the letter ‘I’ ,but it is not, it is sort of ‘Y’ shape.
http://www.vukcevic.talktalk.net/MF.htm
If it is circulation within interior than it the Earth’s core must be highly non-homogeneous.
If you want to simulate the Earth’s magnetic field then instead of having a simple bar magnet, get 3 bar magnets and join them as per graph in the above link. Than try to imagine how mantle circulation or moon movements can create such configuration.

vukcevic says:
December 18, 2010 at 11:55 am
All these assumptions and calculations are misleading. It might be OK if there was a big magnet somewhere in the Earth’s interior in shape of the letter ‘I’ ,but it is not, it is sort of ‘Y’ shape.
No, what you see at the surface bears little relation to what the field is in the core. The higher order multipoles decrease in strength much faster than the dipole and even the quadrupole.

Carla

Leif Svalgaard says:
December 18, 2010 at 3:10 pm
vukcevic says:
December 18, 2010 at 11:55 am
All these assumptions and calculations are misleading. It might be OK if there was a big magnet somewhere in the Earth’s interior in shape of the letter ‘I’ ,but it is not, it is sort of ‘Y’ shape.
No, what you see at the surface bears little relation to what the field is in the core. The higher order multipoles decrease in strength much faster than the dipole and even the quadrupole.
~
Vuks, having a hard time getting my iron ball to spin freely in that Y config. I’ll lean towards an H config with the outer uprights being those 2 cylinders with four ends, Andy Jackson was descriibing in “A new turn for Earth’s rotation.” Now my ball is turning freely again. whaaaaaat
Leif says, The higher order multipoles decrease in strength much faster than the dipole and even the quadrupole.
~
Ok