Geologists: Earth's core & geomagnetism question?

Question

We know the geomagnetic poles reverse, and we know we're due for another reversal pretty soon (within 1,000 years) so do you think this inner geomagnetic upheaval 'agitates' the core, making it hotter and thereby causing it to expand? Is there any other valid geological reason that could make the core hotter?

Also, what is your explanation for why geomagnetic reversals occur? Would you say it's in response to an inner influence within the core (if so what/why), or otherwise an external one such as our approaching proximity to the galactic centre and its possible influence, and/or our current position in the spiral arm of our galaxy? I'm interested in properly thought-out theories please; preferably from actual geologists. Thanks.

PLEASE stop picking on "due" or other words, or the way this might be worded... please just get the overall gist of the Q and try to answer it. Thanks. Plus you don't NEED to be a geologist to reply - I wrote that to mean I'm not interested in wacky answers like it's all down to aliens living in caves, or some such thing. Thanks.

GLENILYND - I haven't said that the reversal, or anything to do with it might cause the core to heat, I'm ASKING if that's possible, because I don't know and wanted opinions - I'm just wondering if this MAY cause core heat to rise (or what would?). Clearly yes there's an "abnormal shift" that you mention, but WHAT causes that to happen? There must be some kind of trigger, or influence?

r.e. galactic centre + our position in spiral arm... I'm not an astronomer, but take a keen interest, esp in what the legend Sir Patrick Moore says, and so I'm damn sure about our position - but just wonder how our position may affect our core/geomagnetism.

GEOLOGISTS: I appreciate your answers very much, however if nobody actually knows for sure what causes/triggers reversals then how are you/they able to discount (for example) external influences? We don't even know for sure what's the exact core composition, or mechanisms within it. Also, how can we say for sure that reversals do not affect the core at all r.e. heat/expansion if we don't know the above facts, and have no human historic records (except legends) of the effects of previous reversals?

qrpr1964 = Brilliant information! You wrote... "Geologists have a number of ways of measuring palaeo-heat-flow variations and it does not vary with palaeomagnetic reversals." This is just the info/insight I'm seeking... how is this done? Over what kind of time period does each data set cover; i.e. would the temp record account for a period less than 100 years at the margin inbetween reversals when possibly the temp peaked?? THIS is the info I'm DYING TO KNOW! I shall now get on with some enquiries into this line.

Answer 1

Another geologist speaks...

actually mnrlboys answer above is a pretty good one.

The mechanism for polar reversal really is very poorly understood, although most believe it to be due to some changes in the circulation, or convection with in the inner iron-nickel rich core (as opposed to extra-terrestrial causes). What triggers that reversal remains unknown, suffice to say that fluid dynamic processes in the inner core of which we have no direct knowledge are possibly non-steady state and therefore possibly prone to "spontaneous" shifts or flips subject to some other feedback loop or a forcing mechanism like an orbital wobble? This is the realm of physics, of which I am not qualified to speculate further!

We have never (as a human race) experienced a polar reversal, although we do know that they happen on a reasonably regular basis (we can measure the palaeo-polarity from studying the orientation of magnetic crystals "frozen" in igneous rocks like microscopic compasses). We are seeing a steady decline of the Earth's magnetic field right now, a possible pre-cursor to a reversal in the not-too-distant future (100's of years?). That, plus the frequency of reversals known from the geological past is what geologists mean when we say we are "due" another reversal. It is of course not a precise prediction!

When the reversal happens, geological evidence suggests it could be very rapid indeed (perhaps a few years even), as some palaeomagnetic reversals have been found to have occured between discrete lava flows. That said, this isn't an argument for creationism a la ChasChas's answer.

There is absolutely no evidence to suggst that a magnetic reversal will induce changes in heat flow. In terms of the core, which is "liquid", it's likely to be in a pretty agitated state anyway, in terms of fluid dynamics, but we have no way of knowing this for sure. The overall heat flux is for all intents and purposes right now a constant, being sourced from long-term radioactive decay of elements in the earth's core. However, long-term pertubations in the thermal gradient are caused by tectonic processes (crustal thinning, rifting and associated vulcanicity). Geologists have a number of ways of measuring palaeo-heat-flow variations and it does not vary with palaeomagnetic reversals. These magnetic reversals happen at a greater frequency in terms of geological time.

ADDITIONAL INFORMATION:

See: http://wwwrses.anu.edu.au/~jean/GEOL3005/PlateTectonics/Magnetic.html for details of magnetic field reversals in the geological past.

Geologists can measure palaeo-heatflow in a number of different ways in strata penetrated by boreholes. OK, this is really technical stuff. It's fraught with difficulties and assumptions and wide margins of error. Also we are dealing with time periods of millions of years (not hundreds!) so sampling frequency is an issue. The techniques involved (for example, Apatite Fission Track Analysis /AFTA and Vitrinite Reflectance) are indirect, in that they measure mineralogical changes due to heat that are a function of both temperature and depth of burial (the two are inexorably linked). You can back-out maximum depth of burial by other means (due to tectonics, it's not necessarily the same as current day depth of burial), which in itself is an imprecise calculation, and then estimate a value for maximum palaeo-heat flow at a given depth and age of strata. There is often quite a lot of "scatter" in the data, so the bottom line is that you will not see the sort of very short term variations that you are seeking.

That said, your question has got me thinking. You'll see on the link above that the late Cretaceous (85 to 65 million years ago) was an anomolously "quiet" or inactive period in terms of magnetic reversals, in contrast to the much higher frequency of reverasls seen during the Tertiary (65 million years ago to present). The end of the Cretaceous coincided with immense volcanic activity, in India and in the North Atlantic, suggestive of a heat flow event (geologists call these "mantle plumes" without really knowing much more). So in a broad sense, on a time scale of millions of years rather than hundreds, there may be some sort of link with palaeomagnetism, heat-flow variation and vulcanicity.

Answer 2

I'm a geologist, and I'm happy to address your questions the best I can:

I can't think of anything about geomagnetic reversals that would make the core hotter, or cause it to expand... Any change in a system is bound to involve the transfer of a little energy, but a geomagnetic reversal is only going to involve the realignment of whatever magnetic domains control the earth's magnetic fields. Changes involving magnetic orientation are definitely not going to involve enough energy exchange to change the temperature of the core by a significant amount. I can't think of anything else that would cause the core to become hotter either... it will likely just cool slowly over an additional billions of years.

As for why geomagnetic reversals occur, this is definitely a poorly understood phenomenon and is being actively researched. The most prevailing thought is that it has to do with the circulation of liquid iron in the outer core, and that perhaps these currents periodically shift the orientation of all the iron the core contains. Some geophysicists are are working on running models of the core based on fluid dynamics equations, and depending on how you set up the model, some are seeing periodic shifts in the overall magnetic field produced by the model over time. But of course, that doesn't necessarily mean that these models are right. However, it is very safe to say that the mechanism has to do with processes going on inside the core, and not by our position in space (which would not be expected to have any influence on the earth's magnetic field).

I hope this helps... feel free to e-mail or add to your question if you have any more thoughts.

Answer 3

I don't think it's accurate to say that we're "due" for a magnetic reversal. Not much is known about why it happens. We can observe the intervals in the past and make vague predictions. What makes you associate magnetic reversals with an expansion of the core? I've never heard of any theory about that. (I'm not trying to be rude I just honestly have no idea)

The only reason I could think of for the core to get hotter is if a natural fission reactor were to form or has formed in the earth's core. They have been observed in a mine in Gabon, Africa. It is possible that there are fission reactions taking place within the Earth.

The more widely accepted theory is that the heat within the Earth is left over from when the planet formed. Large rocks and other material orbiting the sun slammed into one another. The heat energy from these impacts caused the rock to melt and stick together, eventually forming the Earth. The outside eventually cooled and hardened trapping heat inside. Most scientists tend to believe that the core of the Earth is as hot as it will get and is cooling.

It seems unlikely the the reversals are caused by anything external to the Earth. This is just my own personal speculation but the reversals could be caused by an abnormal shift in the orientation of the Inner core. The inner core's rotation is what is responsible for the magnetic field in the first place. I think the core itself could have developed a north and south pole. just like a magnet. If the core normally rotates in a similar fashion as the earth and we called that "side to side rotation". Then gradually the core makes an "end over end" rotation changing the location of it's own poles that could cause the reversal. Again, this is my own personal speculation and I make no claims to it's accuracy it is nothing more than an educated guess.

Answer 4

Not a full answer to your question, but I'd just like to point out that we're not "due" for another magnetic reversal. We can tell when the reversals occurred in the past and estimate the time span between them by examining the geological record on the sea floor. However the belief that we can therefore project those measurements into the future and predict events with any certainty is a fallacy.

As stock brokers say past results are not a predictor of future performance.

Answer 5

There is evidence that the reversals were rapid.
Check here for detailed articles
http://www.creationontheweb.com/content/view/1233/

The standard explanation is:
The earth’s magnetic field is generally considered by most geophysicists to be associated with electric currents in the earth’s innermost region, the core, which is believed to consist of a metallic iron-nickel mixture, and is presumed to operate like a dynamo. These electric currents are believed to be produced by the slow circulation of molten material that carries unequal amounts of positive and negative electric charge.

But others have found evidence to support:
they propose freely decaying electric currents in the earth’s core.This mechanism accounts for the real-time decay of the earth’s field over approximately the past 150 years, the current generated from such field decay correlating well with calculations of the amount of current actually present within the core. In addition, it can account for the magnetic reversals recorded in the rocks having taken place in a matter of only days to weeks!

Answer 6

There is evidence that the poles have shifted in the past, so it CAN happen.
Are we 'due' for a shift? I don't know, but if it happens I certainly hope that the shift is slow.
Magnetic flux can induce electrical current in a conductor and since the planet's core is iron, there is probably a fairly large current flowing there. Current through resistance equals heat.

Answer 7

I'm not a geologist so I won't answer the question but I do have a book called 'path of the pole' by Charles Hapgood (foreword by Albert Einstein)
I still can't answer the question as I haven't fully read the book but i thought you'd like to know about it.

Answer 8

Sounds like those pesky gofers are causing trouble again!!!