yeah, i know, this has probably been discussed before; but i have some specific questions that i don’t feel like reading 3 entire threads to find the answer. my first question is, what exactly causes them? i have been told by one of my high school teachers that Noah’s Flood shifted the poles or something approx. 32 degrees. whether you believe the story of the flood or not, theoretically, would something of this nature shift the poles like this? throughout history, what has been said to shift the poles before? (i’ve heard it’s supposedly happened a couple times already.) and, finally, i have been told that the poles are going to eventually shift in the (relatively) near future; what do scientists predict should cause this next shift?
The short answer to all your questions is that the cause of the magnetic pole flips is not exactly well known. It has something to do with the way the magnetic field is generated inside the Earth. We have a vague notion of how this works (electrical currents flowing in the molten iron and nickel in the outer core) but the details are still being worked out.
The shifts in the poles have something to do with how those currents deep inside the Earth change over time. The Earth’s magnetic field is not affected by events that occur at the surface of the Earth, and the polar flips are not caused by external events (as far as we know.)
We know that the magnetic poles tend to reverse themselves around once every 300,000 years (but this varies a lot!). Many reversals of this type are recorded rocks. In a lava flow, iron particles are free to align themselves with the Earth’s magentic field like tiny compass needles, but once the lava solidifies, the iron particles are frozen in place. So we can look at a place where new rock has been formed steadily over time and see stripes, where the iron particles are oriented toward the north, then to the south, then to the north, etc. We can measure the strength of the magnetic field as well as its orientation at the time that the rocks solidified.
The reason that some scientists think a magnetic field reversal may be coming is that the Earth’s magnetic field has been decreasing pretty steadly for the past 150 years, and the location of the north magnetic pole has been moving, something like 50 km in the past 200 years. Also, the last polar flip was 780,000 years ago, so we’re kind of overdue. However, while the magnetic field does tend to weaken before a reversal, it also fluctuates up and down normally all the time.
Here’s a really cool article about how the Earth’s field has changed recently, and also over millions of years:
Just to clarify something: magnetic polarity reversals are one of the few Earth processes that are completely random in terms of timing. There is no way to be overdue for a reversal, in the sense that “X number of years have passed since the last one, and now we should have another.” Polarity intervals (called chrons) have been as short as a few hundred thousand years, and as long as 70 million years (the Permo-Carboniferous superchron). With the knowledge we have right now about the Earth’s magnetic field, we have no way to forecast when the next reversal will happen, although we can speculate about the possibility of one in the geologically near future because of the field weakening that Podkayne mentioned.
Sediments and sedimentary rocks with a sufficient number of magnetic grains will also capture the magnetic field orientation, and in fact provide the best means of getting at magnetic polarity information over the long term (since sediments by volume comprise more of the rock record than volcanic rocks do, in most places). It can be a little harder to tease the data out, and date it as precisely as one could do with volcanic rocks, but the redundancy of measurable and datable sedimentary successions helps to pin down the reliability of the geomagnetic time scale.
This page has a good summary of the basics about the Earth’s magnetic field and paleomagnetism, to complement the info in Podkayne’s link.
The notion that the floods shifted the poles comes up in creationist literature and other pseudoscience, but has no creedence whatsoever, whether you are a believer or not.
Various crackpots on the net:
You make me fear for our future.
Are you sure about that? It was my understanding that the Earth’s dynamo, and the processes which cause it to reverse, are similar to those in the Sun, and the Sun’s magnetic field reverses on a fairly regular schedule of once every 11 years. While I can understand that the Earth’s dynamo would be less regular, due to the lesser fluidity of the dynamo and friction with the Earth’s solid portions, shouldn’t one still expect to see a rough periodicity?
no name face, it’s impossible to discuss the physical effects of the Flood, since it’s impossible to physically discuss the Flood at all. One would have to explain where all that water came from, and whither it went afterwards, since there isn’t enough water on the Earth to flood the whole planet (if there were enough currently, we’d still be flooded).
even supposing all the continents hadn’t spread yet and were still one, as many believe? also, the flood, if it existed, might’ve just covered the entire world as people knew it at the time. what would be the point in flooding areas people didn’t even know existed? also, some say that some of our continents that exist today didn’t even exist back then (north america being one of them. i don’t know if there were any others.)
If you weren’t too lazy to read the previous threads you might learn a lot!
There was never a worldwide flood at any time.
There have been millions of floods smaller in extent, but despite many speculations there is and can be no proof that any of them were the one referred to in the Noah’s Ark story, which is merely a mythic tale retelling an older legend in any case.
If you are going to a public school you should report your teacher for teaching religion in class.
If you are going to a parochial school, well, perhaps a public school would be better for you and your further scientific education.
That’s true. North America didn’t exist until Ar-Pharazôn broke the Ban of the Valar and set foot on Aman. Only after Illuvatar bent the world and removed Aman from Arda was the space where North America is now freed up. Then some continants formerly on the east side of the world, east of the Dark Lands, moved to where Aman once was. They became North America.
Now I feel better. I may be behind on some things, but at least it hasn’t been 780,000 years since I last flipped my magnetic field.
Yup, I’m pretty sure. Paleomagneticists and geomagneticists love to discuss this particular issue, because finding evidence of periodicity in magnetic reversals would go some distance in the overall effort to understand what makes the Earth’s magnetic field tick. It would appear that the interactions between liquid outer core and solid inner core and mantle complicate matters considerably compared to the dynamics of the Sun’s gases.
Here’s an abstract from a paper relevant to the topic:
Gallet, Y. and Courtillot, V., 1995, Geomagnetic reversal behaviour since 100 Ma: Physics of the Earth and Planetary Interiors 92:235-244.
Some researchers do occasionally refer to average reversal frequencies for a given time interval. The reason that they can only do that for particular segment of time is because over the last 180 million years, there have been a number of abrupt changes in reversal frequencies. Plate tectonic processes, which do not operate with any sort of periodicity, have been linked to these changes in reversal frequency (Ricou and Gibert, 1997).
To be even-handed about this, there has been a suggestion that the magnetic field’s reversal behavior may be reflecting the behavior of a self-organized complex system (Jonkers, 2003). If it is, then it wouldn’t be appropriate to say that reversal are totally random, but it still doesn’t make the pattern of reversals easily predictable, especially given those abrupt changes in reversal frequencies we see in the paleomagnetic record.
There are complicating issues in the discussion (e.g., whether one considers “tiny wiggles” in the paleomagnetic record to represent geomagnetic excursions [deviations away from the dominant polarity of a chron] or full-blown short-lived reversals), but for now, the general consensus continues to lean toward a stochastic model of reversal frequency over the long term.
For much shorter time scales (i.e., the last few thousand years to hundred of thousands of years), there have also been suggestions that geomagnetic intensity (not polarity) fluctuated in a periodic fashion. However, there is the problem of teasing out climatic effects on the bulk composition of sediments vs. actual changes in intensity. When the climatic effects on sediment composition are accounted for, there’s no periodicity in the frequency of geomagnetic intensity either (Dinares et al., 2002).
Dinares, T.J., Sagnotti, L., and Roberts, A.P., 2002, Relative geomagnetic paleointensity from the Jaramillo Subchron to the Matuyama/ Brunhes boundary as recorded in a Mediterranean piston core: * Earth and Planetary Science Letters* 194:327-341.
Jonkers, A.R.T., 2003, Long-range dependence in the Cenozoic reversal record: Physics of the Earth and Planetary Interiors 135:253-266.
Ricou, L.E., and Gibert, D., 1997, Magnetic reversal sequence studied using wavelet analysis; a record of the Earth’s tectonic history at the outer core: Comptes Rendus de l’Academie des Sciences, Serie II. Sciences de la Terre et des Planetes 325:753-759.
Another euphemism I hadn’t previously heard. You kids and your slang!
It’s a bit late now but the OP looks awfully like homework questions.