The Earth’s magnetic field, but explaining precisely how that dipole is generated and maintained is not simple at all. The field originates deep in the Earth, where temperatures are far too high for any material to maintain a permanent magnetisation; the dynamism that is apparent from the wandering of the magnetic poles with respect to the spin axis (secular variation), and the quasi-periodic flips in field polarity, also suggest that some process is actively generating and maintaining the geomagnetic field. Geophysicists therefore look to the most dynamic region in the planetary depths, the molten outer core, as the source of the force that directs our compass needles.One of the more important processes going on in the core is the slow growth of the solid inner core at the expense of the outer core, as the centre of the Earth loses heat to the mantle, and ultimately the surface. As the iron crystallises, it releases latent heat, generating thermal buoyancy forces. Additionally, seismic measurements show that whilst the outer core is much less dense than experiments and calculations predict, this deficit is much smaller in the inner core; therefore crystallisation also leaves behind the lighter elements that make up around 10% of the outer core (it’s not entirely certain what these elements are, but sulphur is a popular candidate), generating strong compositional buoyancy forces.
The outer core is the source of the geomagnetic field. Larger image Earth's magnetic field comes from this ocean of iron, which is an electrically conducting fluid in constant motion. Sitting atop the hot inner core, the liquid outer core seethes and roils like water in a pan on a hot stove. Scientists believe Earth's magnetic field is generated deep inside our planet. There, the heat of the Earth's solid inner core churns a liquid outer core composed of iron and nickel. Magnetic field can be seen as lines like those revealed by the alignment of iron fillings on a piece of paper 2. Earth's magnetic field point down at the into the ground at the north pole and out and up at the south pole 3. The lines of force look like a dipole mag.
Together with a possible contribution from heat generated by radioactive decay, these buoyancy forces drive vigorous convection of the outer core, with flow rates of the order of 10 kilometres per year.As you may dimly remember from school, the motion of a conductor in a magnetic field; currents also generate. The iron in the outer core is a conductor, so its motion in the presence of the existing geomagnetic field induces electric currents, generating new magnetic flux, as well as forces that modify the pattern of convective flow. The key to a stable, self-sustaining geodynamo is that these processes feed back on each other, until the pattern of induced currents – both electrical and convective – generates a magnetic field that has the same, or almost the same, configuration as the input field, reinforcing and maintaining it over geological time. The field induces currents which generate the field. This is no free lunch: Ohm’s law dictates that resistance to the electrical current flow will cause energy to be lost from the system, so without the external input of energy from convection, within a thousand years or so the field would weaken and die.You can get your head round this idea without developing too much of a headache, even if the ‘geodynamo’ looks nothing like any electrical generator that humans have ever imagined. However, matching this general account to the actual behaviour of the actual magnetic field of the Earth, in all its polar wandering, polarity reversing, glory – is not so easy, not least because many of the physical parameters that control convective flow, such as the viscosity of the outer core, are poorly constrained.
Plus, magnetohydrodynamic modelling is as fiendishly complicated as its name suggests. Nice explanation – I’ve always had trouble twisting my mind around studies of the magnetic field, but you explained that very nicely. Those animations are great, too – perfect for showing someone what a magnetic field reversal would look like.(BTW, I’ve run across a lot of non-geologists who think a magnetic pole reversal involves the Earth physically flipping over, with devastating consequences for everything on the planet.
Earth Magnetic Field Is Twisting Machine
That animation would be a good way to illustrate what’s more likely going on.). Kim – if that is so, maybe I should add something to my ‘misconceptions in geology’ list!Callan – the “true polar wander” that Joe Kirschvink is discussing is actually related to plate motions rather than the behaviour of the magnetic field – it’s a proposed motion of the entire lithosphere (all the plates) relative to the spin axis, caused by the Earth trying to minimise its moment of inertia (e.g., when high latitude supercontinents cause a mass excess). It’s very hard to spot, if it has happened at all – possibly a worthy subject for a future post?It terms of the behaviour of the magnetic field, secular variation can cause the poles to wander some distance (10 degrees or more) away from the poles. There are also the periodic excursions and reversals, where the dipole field weakens and the pole wanders to, and across, the equator (it’s also possible that during these periods that there is more than one “north/south pole” randomly dotted about on the Earth’s surface – you can actually see that in the middle panel of the reversal sequence above). However, all these variations take place over (geologically) rapid timescales – even a full reversal only takes about 4,000 years – and all secular variation averages out to a dipole centred on the spin axis over periods of longer that 5-10,000 years. So if you want to use palaeomag to reconstruct plate motions, these variations are relatively unimportant.Daniel – the important thing the realise is that external energy is being fed in to the system to maintain convection – without that, the whole system would collapse.
Okay, convection is driven by the various energy releases from stored potential as it cools, so the field strength stays roughly the same since energy loss to the field is balanced by new energy entering.Question: how’d it get started? Moving conductors in the absence of a magnetic field doesn’t set up a net current anywhere. Would the motion of tiny random magnetic domains be enough to kickstart this, or do we figure Earth had a magnetic moment inherited as it coalesced from the primordial solar cloud?Second question, possibly related: where, exactly, are the currents? The magnetic field is being produced by induced currents, right? So where in Earth’s core could I stick the two probes of an ammeter and measure a movement of net charge?
William: the most obvious source of stray magnetic flux to start the whole thing going would be the sun – or possibly ionized gas clouds in the early planetary nebula.I’m not sure I quite understand the question about currents – but (if you could do so) probes placed at any distance apart in the outer core would probably register some sort of current.Joao: that’s a good question. Quite how birds and other creatures with magnetoreceptors actually use them is not entirely clear. I’d guess that its as an aid to visual cues (such as the position of the sun).
This, plus the slow change in the field from their perspective (it would take several dozen generations for a reversal to happen) may allow them to adapt. On:.: Actually, a (fortunately small) tsunami was generated in the aftermath of the quake.: Wow Chris this was the most excellent explanation of recent Kilauea activity i could find – so.On:.: Note 50 years is the average lifetime of a commercial building a single family home tends more to the 75.: Great blog post! Only suggestion is that the Uniform California Earthquake Rupture Forecast.On:.: Hmmm, I refreshed the page and the ‘last parent standing’ changed, but then settled back to.: Nice graphics, but the last purple ‘atom’ is always fourth from the right on the top row.
I.On:.: great read. I feel lucky to be alive in an age where many scientists before me and current ones who.: I enjoyed this, immensely.
New research from the University of Rochester in New York reveals that life on Earth caught a lucky break 565 million years ago when the collapse of the Earth’s magnetic field was prevented by the timely solidification of the Earth’s inner. The Slow Collapse of the GeodynamoA published in the journal Nature Geoscience provides strong evidence that the Earth was close to suffering a catastrophic collapse of its magnetic field about 565 million years ago.Examining found near Quebec, Canada that date to about half a billion years ago, lead researcher Richard Bono found strong evidence that the Earth’s magnetic field was about 10 times weaker than it is today and getting weaker. Lattices in the crystals—which are sensitive to the changes in the Earth’s magnetism— that the it went through a period of weakness that lasted about 75,000 years, with its weakest point coming around 565 million years ago.This was much longer than it would have been had the weakness been the result of an imminent change in direction or pole reversal, which have occurred regularly in the past. The only explanation would have been the imminent collapse of the geodynamo, the convection currents of the liquid outer core of the Earth responsible for generating the magnetic field.“Liquid iron in the outer core convects, carrying with it magnetic field lines that twist, continuously regenerating the field. Without the convection there would be no core magnetic field,” study co-author John Tarduno. The Earth’s Magnetic Field Isn’t Just About Your CompassThe role this shield around the Earth plays goes largely unappreciated by the public at large, but it is a silent guardian over all life on Earth.Without, the sun’s solar winds, charged particles that are blown out by the sun at millions of miles an hour, would hit our atmosphere without interference.
Over time, this would have a similar effect on the atmosphere as the weathering effect of sand in the desert has on desert monuments. Over time, paint is stripped away, features flatten out, and—given enough time—, the entire statue would be worn away to nothing. And we don’t have to speculate about what it would look like, all we have to do is look at the barren landscape of Mars to understand what Earth could have looked like without a strong magnetic field. Saved in the Iron-Nickel of TimeAt the moment when the Earth’s magnetic field was weakest, life on Earth caught a lucky break.
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Earth Magnetic Field Value
The iron-nickel of the planet began to solidify.Thought to have entirely liquid like the outer core, eventually, the pressure of so much material overhead would slowly force the liquid into an effectively solid state while the surface temperature of this mass would reach a little more than 5,400 degrees Celsius. As time went on, the inner core would grow as the liquid iron-nickel alloy of the outer core would solidify under pressure to add its mass to the inner core.
Is Earth Magnetic Field Constant
This process of solidification, or “nucleation,” provided the essential boost in energy that the fading geodynamo needed.“As Earth evolved,” Tarduno, “the energy to drive convection gradually decreased, until a critical point 565 million years ago marked by the extremely low magnetic field intensity. The growth on the inner core provided a new source to drive convection and the geodynamo.' Thanks to the restoration of Earth's magnetic field, life was able to continue and thrive, with the, the massive growth in biodiversity responsible for animal life, occurring not long after things started turning around 565 million years ago.