View Full Version : Discussion: Field Reversal Takes 7,000 Years

2004-Apr-08, 05:30 PM
SUMMARY: Scientists have known for a long time now that the Earth's magnetic field unexpectedly reverses polarity over long periods of time, but how often this happens was still a mystery. Brad Clement, a geologist funded by the National Science Foundation, has concluded that the reversal seems to happen every 7,000 years, on average. He gathered this data by analyzing deep-ocean sediment cores. One surprise is that the variation seems to alter with latitude - the directional change takes half as long at low-latitude sites as it does at mid- to high-latitude sites.

What do you think about this story? Post your comments below.

2004-Apr-08, 05:36 PM
Okay, I am missing something here, how does it change for different lattitudes?

2004-Apr-08, 08:41 PM
An article was just published a couple weeks ago in one of the AGU journals where the computer model showed that reversals take about 4,000 years to occur. It seems that lithospheric magnetism affects the process and in one of the most bizarre figures i have ever seen, the lines of force are strangely convoluted in the lower lattitudes, like a bowl of spaghetti. For the purposes of illustration, "selected" lines of force were shown, and were shown as having some thickness. In that diagram, when the reversal was paused at that moment, the lines of forces were collapsing and virtually swirling in one area. I havn't finished the article, but I think the gist of the argument is that the crustal magnetism created such significant perturbations in the geodynamic field that the field eventually collapses. By implication, the length of the reversal would seem to be dependent on the position of crustal material at different times of the earth's evolution. It's interesting that the field data of the news story is essentially supported by the mathematical model. The citation is: Wicht, J. and P.Olson(2004), A detailed study of the polarity reversal mechanism in a numerical dynamo model, Geochem. Geophys. Geosyst, 5,. It is worth tracking down. There are 3 animations that can be downloaded. Now

John LaCour
2004-Apr-09, 01:31 AM
This is BAD NEWS! Image 7,000 years with little or no magnetic field. Solar wind ions and radiation will pass straight to the atmosphere creating auroura over the entire planet. The safest place to be when that happens would be the poles, where you could go 6 months with little or no direct sunlight.

2004-Apr-09, 03:47 AM
Originally posted by damienpaul@Apr 8 2004, 01:36 PM
Okay, I am missing something here, how does it change for different lattitudes?
During the process of reversing polarity, the begining anomalies in the magnetic field occur on or near the equator. It takes more time for the anomalies to reach the poles, therefore making it longer for the actual reversal of the magnetic field at that latitude.

Thomas Foster
2004-Apr-09, 03:51 PM
Field Reversal Takes 7,000 Years to COMPLETE… and has concluded that for the last 15 million years the reversal seems to happen every 250,000 years, on average … although the flips are not periodic, meaning they don't adhere to a schedule of even intervals.



2004-Apr-09, 04:03 PM
They neglect that the weather would come from the east, and all tornados, hurrcanes, etc, would rotate clockwise, in the north, and counter clockwise in the south. the opposite of now.

The earth's Bloch Wall, or area of internal flux, between the tropic of capricorn and cancer, where the N & S poles meet, changes posistion, somewhat to start the polarity change.

All bar magnets have this, called a diamagnetic vortex point of no magnetism.

You can find this area with a compass on a regular bar rmagnet, just hold the compass a couple of inches from the magnet and slowly move it up and down the lenght.

Where it points east and west is the neutral center or point of no magnetism, or diamagnetic vortex point.

The internal spin of the internal flux, is counter-clockwise presently,N, and clockwise S., and a sort of figure 8 where they intersect in the middle.

This is not the external lines of force you see with iron filings on paper, over a bar magnet, but unseen internal opposite spirals.

The earth is much larger and more complicated in this respect, as well as the sun, and all planets.

Hot bodies ,such as the sun reverse in years, while cold bodies take thousands of years, if not more.

The so called experts should study this fact, as electromagnets have the same feature, as do horseshoe magnets, or any shaped magnet.



2004-Apr-09, 05:00 PM
"The so called experts...." I need an autoresponse message for people who think they have the ultimate wisdom and make cracks like that in an eneven playing field. Who the hell are you? Maybe nobody is "neglecting" anything yet. They'll get around to it, I'm sure, once they have some time to post a message here. You know, after teaching some classes, dinners with the Dean, office hours for the students, working on the research-- all that crap that eats up a day. Somehow, i suspect the people who study geomagnetism know something about other magnets. The "so called experts", that is.

Algenon the mouse
2004-Apr-09, 05:16 PM
I have always thought the earth was more like an electric magnet due to the spinning around an iron core. Aren't we overdue for a change?

2004-Apr-09, 05:18 PM
Not to mention that in a lot of cases, academics are required to also do commercial work like consultancy as well.

2004-Apr-09, 11:55 PM
Thats an interesting find. B)

2004-Apr-10, 02:45 AM
Originally posted by Prime@Apr 9 2004, 12:03 PM
They neglect that the weather would come from the east, and all tornados, hurrcanes, etc, would rotate clockwise, in the north, and counter clockwise in the south. the opposite of now.

I always thought the direction of weather was a result of the coriolis effect. :huh:

2004-Apr-10, 05:40 AM
I believe this is correct. The Coriolis effect. Things at the equator are moving faster than things at the poles. When air masses move from north to south in the northern hemisphere they turn westward because the earth is moving faster to the east as the air moves south. Air moving north moves eastward. The intersection causes a counter-clockwise rotation in the northern hemisphere. The earth would have to reverse its rotation to change this.

2004-Apr-13, 02:18 AM
Doesn't iron loose its magnetic abilily after it reaches a certain temperature?

2004-Apr-13, 03:44 PM
That process is most likely a kind of dynamic action in which the flowing and convecting liquid iron in Earth's outer core generates the magnetic field, geologists believe.

So if a planet has a core that is not a magnetic metal, would it not have a magnetic field? (is that even possible?)

2004-Apr-28, 07:23 PM
So how long ago did it turn polarities :o :(