Reversal of the Earth's Magnetic Field

[subgenius]

For a couple of years I've mentioned to people that we're way overdue for a reversal of the earth's magnetic field. The sun does it every 11 years.
Earth's pattern is every couple of hundred thousand years. The last one, however was 780,000 years ago, so we're seriously overdue. Our magnetic field shields us from bad radiation. The strength of the field has been dropping precipitously, and there have been magnetic anomalies detected, especially in the South Atlantic.
All of this confirmed on PBS "Nova" tonight.
Could be any time.
Just thought you'd like to know, in case you didn't have enough to worry about, or in case you worry about trivial things.
Sorry, no link to "Nova" yet, it just aired tonight.
I used to live every day as if it were my last, but I got tired of making funeral arrangements and weeping all day.
We're All Doomed, and That's the Good News.

[The Don]

I'll go and buy some compass paint just in case

[Cecil]

Planet X is coming! Planet X is coming!

Head for the hills...err...bunkers on the dark side of the moon!

[MRC_Hans]

A pole reversal is probably upcoming, some say it is already in progress. This has made a lot of woowoos busy, lately.

Some of the more illustrious of them imagine that the planet will actually somehow physically topple in its orbit, causing widespread disaster. This is, of course, nonsense. What may change is the magnetic poles, as they have done repeatedly during the history of Earth. The change is quite abrupt, on a geological time-scale, lasting only a century or two.

During the change phase, poles will move, probably divide, and in long periods, Earth's magnetic field may become very weak, even almost disappear.

This will make compass navigation difficult, and presumably, the belts of ionized particles, the van Allen belts, will temporarily disperse. The van Allen belts protect us from some of the radiation from space, so it can be assumed that the background radiation level on the surface will rise considerably during long periods.

Increased radiation will mean increased incidence of cancer, mutations, and other niceties, but it will not mean disaster. Pole changes in the past cannot be linked to archaelogical evidence of mass extinctions, triggering of mass species diversion, or the like.

So, we're not doomed, but interesing things may happen.

Hans

[Keziah Mason]

Hey, bring it on. I got my GPS unit - who needs a stone age compass? :cool:

[LuxFerum]

how many time will that process take?

[Small Town Jesus]

Originally posted by subgenius
For a couple of years I've mentioned to people that we're way overdue for a reversal of the earth's magnetic field. The sun does it every 11 years.
Earth's pattern is every couple of hundred thousand years. The last one, however was 780,000 years ago, so we're seriously overdue. ...

Just out of interest, how is it known when the earth's magnetic field last reversed? Is there some kind of physical evidence?
Also how often do the other planets in the solar system have pole reversals?
(I know I could look the answers up on the net but I thought I'd give you guys a chance to show off! You love to do it and I love to read it.) :)

STJ

[The Don]

Originally posted by Small Town Jesus


Just out of interest, how is it known when the earth's magnetic field last reversed? Is there some kind of physical evidence?
Also how often do the other planets in the solar system have pole reversals?
(I know I could look the answers up on the net but I thought I'd give you guys a chance to show off! You love to do it and I love to read it.) :)

STJ

Polarisation of iron particles in igneous rock. When a volcano produces lava, the iron particles align with the current magnetic field. Different rocks of different ages have diffrent alignments

[Tricky]

Originally posted by The Don
Polarisation of iron particles in igneous rock. When a volcano produces lava, the iron particles align with the current magnetic field. Different rocks of different ages have diffrent alignments
Indeed, magnetic mapping of the sea floor shows continuous bands of magnetic polarity in the basalt of the ocean crust. This was one of the clinchers for proving continental drift. The pattern of magnetic bands on either side of the rift (where spreading occurs) was identical.

By radiometric dating of the rocks, we can get pretty precise dates on the magnetic reversals, and Subgenious is correct that we are, on the average, overdue for one. But the intervals vary quite a bit and we are nowhere near the longest "unreversed" period.

As far as I know, nobody is certain what causes them. Sunspot activity has been suggested, but we don't have good tools for telling when sunspot activity was high in geologic history. But maybe this big flare up recently really is signifying a time of change.

Expect an increase in bipolar disorders.

[Tmy]

Dont the poles move around quite a bit. Magnetic north is not constant, right?

BAH! Dont worry, our alien overlords have already intsalled magnetic stabilizers deep in the earths core.

[Tricky]

Originally posted by Tmy
Dont the poles move around quite a bit. Magnetic north is not constant, right?

Also true, but in a fairly predictable manner. Comparble to the "wobble" of a gyroscope.

Geology field books contain tables to show you how to adjust your Brunton compass to correct for magnetic north. The cheaper Tate's compasses do not have this feature, hence the term

"He who has a Tate's is lost."

[Small Town Jesus]

Thanks guys. Fascinating stuff!

STJ

[Doubt]

I am going to be so pissed off if I have to buy new compasses!

Of course, we will probably all be dead before a reversal is anywhere near complete.

The Nova show was interesting. At the start of it I was wondering if they had gone woo-woo on us. But they did not og off the deep end.

[Tmy]

Originally posted by Tricky

hence the term

"He who has a Tate's is lost."

HA! If i had a nickle every time I heard that one......Id have 5 cents.


What was Earth like 800k years ago? Any catastrophic changes aroudn the last switch

[subgenius]

The science of the show was great.
When pottery is made it creates a record of the magnetic field existing at the time, as it cools after being fired.
Likewise volcanic rock.
Although the total shift will take hundreds of years, as they showed, its a fits and starts kind of thing with major changes occurring sometimes in the course of a day.
Neat how in the past (I guess that's a redundancy) meticulous records were kept by English sailors of the variation of magnetic north, and how this helped in the present research.
My sense is that the effects will be more devasting than the show, and the above posters feel.
Seems like it is likely to cause disruption of a lot of electro-magnetic devices, satellites, communications, and such. (Wearing my tin foil hat and lead lined jock strap doesn't seem so wacky now does it?)
Quite a light show from the aurora being visible often if not constantly in different parts of the world.
Random thought: If they knew the world would end in say 3 weeks, would it be wise to tell everyone?
I think we all individually would want to know (so you can stop going in to that miserable job), but it sure seems like it would cause a bit of disorder.

[Andonyx]

What's going to be curious is the migration and hunting patterns of species that use the magnetic field to navigate.

[fishbob]

As far as I know, there is no evidence in the fossil record of any correlation between magnetic reversals and extinctions. However, I think we should go into the tinfoil hat business. There is a fortune to be made.

I missed the show, dammit. Did the show mention any of the work by Brooks Elwood? He does paleomagnetic analysis of almost anything - clay pots to volcanic flows.

[DrChinese]

Originally posted by Andonyx
What's going to be curious is the migration and hunting patterns of species that use the magnetic field to navigate.

I wasn't aware there were any. I know there has been speculation about some species, including sharks.

[Tricky]

Originally posted by DrChinese
I wasn't aware there were any. I know there has been speculation about some species, including sharks.
I think he means NRA members.

[Andonyx]

Originally posted by DrChinese


I wasn't aware there were any. I know there has been speculation about some species, including sharks.

I was thinking more along the lines of Birds. My understanding is that many species of birds that migrate south for the winter do so by the magnetic poles. But biology is not a strong point so maybe i'm mistaken.

I thought certain sharks had receptors under their snouts that were sensitive to EM fields in order to find small prey buried in the sand or that they couldn't see.

[Andonyx]

A new study suggests that birds use the Earth's magnetic field to plan dining locations along their migration route. These culinary stopovers are critical to the success of the migration because, according to a second study, the fatter the bird, the more efficiently it is able to fly.
How birds obtain precise information about their geographical location and determine exactly where to stop and eat has puzzled scientists for decades. A study published in the November 1 issue of the journal Nature says that the cue may be magnetic.

From National Geographic - http://news.nationalgeographic.com/news/2001/11/1102_TVbirdflite.html

Lots of maybes in this article, but food for thought.

[xouper]

according to a second study, the fatter the bird, the more efficiently it is able to fly. That seems counter-intuitive. But on reading the rest of the article, that statement seems a bit misleading. A fatter bird still requires more energy to fly than a leaner bird. It just requires less energy per pound. Which of course, still seems counter-intuitive. But then, many things about flying seem counter-intuitive.

[EdipisReks]

great Nova last night. i loved the rock song about the magnetic field that played all through it. :D

[LW]

Originally posted by Tricky

Geology field books contain tables to show you how to adjust your Brunton compass to correct for magnetic north. The cheaper Tate's compasses do not have this feature, hence the term

"He who has a Tate's is lost."

Apart from geographic surveyors no one walking on the ground really needs to take the difference between true and magnetic Norths into account. Well, maybe it would be better to add persons walking close to the poles to the list.

The errors caused by the difference are easy enough to correct by looking at the map. And if you don't have a map, you are already hosed if you hit a magnetic anomaly. Those anomalous areas are surprisingly common at some places. I have a few navigation maps from Lake Saimaa (in Southern Finland) and every map sheet shows several small areas where compasses are unreliable. An extreme example of this behavior happens at Kostamus in Eastern Karelia where lies large a stretch of land (~10 km long strip, or so) where compasses point to West because of large iron deposits in the ground.

[peptoabysmal]

Originally posted by EdipisReks
great Nova last night. i loved the rock song about the magnetic field that played all through it. :D

Yeah, what was that noise? A new millenium version of "Little Boxes"?

http://www.ocap.ca/songs/littlbox.html

I got the impression from the show that they didn't know exactly when it would happen or how long it would last. One pole shift took 3000 years. One thing is for certain we could be the first Homo Sapiens to experience it. What about the possible cancer risk from increased exposure to cosmic rays? Will humans in the near future be wearing space suits tailored to living on Earth?

[richardm]

Originally posted by subgenius
When pottery is made it creates a record of the magnetic field existing at the time, as it cools after being fired.


Erm... How does that work as a record, exactly?

I fire a pot and it cools, and the particles align themselves with the magnetic field.

Since I don't know which way my pot was facing when it cooled, how can I use it to tell me anything about the magnetic field at the time? :confused:

[HarryKeogh]

i remember my 7th grade science (and homeroom, gym, crafts et al) teacher saying compasses work because there is a large natural magnetic deposit of iron by the north pole that the needle is attracted to.

:nope:

[Doubt]

Originally posted by LW


Apart from geographic surveyors no one walking on the ground really needs to take the difference between true and magnetic Norths into account. Well, maybe it would be better to add persons walking close to the poles to the list.


Not true, unfortunately.

I do spend a fair amount of time doing orienteering and adventure races. Orienteering maps are based on magnetic north, so no correction there is needed.

Adventure races normally use US Geological Survey maps. In this area the difference is slight and you can get by without a correction if you are only traveling a short distance. The Pacific Northwest is a different story. I have old maps of Ft. Lewis, Washington where the difference is more than 20 degrees between magnetic and true north.

I was not joking in my fist post in this thread when I mentioned having several compasses.

[subgenius]

Originally posted by richardm


Erm... How does that work as a record, exactly?

I fire a pot and it cools, and the particles align themselves with the magnetic field.

Since I don't know which way my pot was facing when it cooled, how can I use it to tell me anything about the magnetic field at the time? :confused:
Although I'm no expert, the pottery doesn't record the direction of the field, and wouldn't show a change, since the last "flip" occurred 780,000 years ago. It does, however, record the intensity of the field, and a study shows the intensity to be dropping (relatively) precipitously.

[xouper]

subgenius: Although I'm no expert, the pottery doesn't record the direction of the field, and wouldn't show a change, since the last "flip" occurred 780,000 years ago. It does, however, record the intensity of the field, and a study shows the intensity to be dropping (relatively) precipitously.I'd like to put forth two questions for consideration.

At its current rate of decreasing intensity, how many years before the Earth's magnetic field strength reaches zero? (This question contains some intentional oversimplifications for the sake of not asking a torturously complicated question.)

Is the Earth's magnetic field stronger or weaker today than it was 50,000 years ago?
I apologize if these questions have already been asked and answered (I missed the Nova episode, unfortunately). But if not, perhaps the answers might be of some interest. :)

[clk]

Originally posted by xouper
I'd like to put forth two questions for consideration.

At its current rate of decreasing intensity, how many years before the Earth's magnetic field strength reaches zero? (This question contains some intentional oversimplifications for the sake of not asking a torturously complicated question.)

Is the Earth's magnetic field stronger or weaker today than it was 50,000 years ago?


Good questions. Also, at what rate does the magnetic field decrease? Linearly? Inverse-exponentially?
Thanks.

[dsm]

Originally posted by subgenius
For a couple of years I've mentioned to people that we're way overdue for a reversal of the earth's magnetic field.

Ummm, why wasn't this in the "Science" forum?

:confused:

[Andonyx]

Originally posted by dsm


Ummm, why wasn't this in the "Science" forum?

:confused:

I believe subgenius has taken a page from McCluhan and believes this event to be near enough as to consider it a "current" event.

[Tmy]

Its a known fact that men have a better sense of direction because we have more iron in our bodies than women and are better tuned in to the mag field.

Thats why we dont ask for directions!:p

[LW]

Originally posted by Doubt


Not true, unfortunately.

I do spend a fair amount of time doing orienteering and adventure races. Orienteering maps are based on magnetic north, so no correction there is needed.


OK, let's then add to the list all persons who want to run.

Us who leisurely stroll in the forest can constantly check from the map where we are so we catch the errors rather quickly.

Thinking yet again, I'm now speaking from context that there are landmarks almost everywhere. I agree that if you are traveling in an area without clear landmarks then, yes, you should know where your compass points.

[Luke T.]

What does this mean for Feng Shui? Will everybody have to move their furniture?

[subgenius]

Originally posted by Luke T.
What does this mean for Feng Shui? Will everybody have to move their furniture?
All the bicycle chains in China will snap at once.

[DrChinese]

Originally posted by Andonyx
I was thinking more along the lines of Birds. My understanding is that many species of birds that migrate south for the winter do so by the magnetic poles. But biology is not a strong point so maybe i'm mistaken.

I thought certain sharks had receptors under their snouts that were sensitive to EM fields in order to find small prey buried in the sand or that they couldn't see.

There is a lot of speculation about sharks, but I haven't seen any convincing arguments. Study has been minimal, and has not produced the expected results in many cases. Most evidence is anecdotal.

Given that the force falls with the square of the distance, and that living matter is essentially neutral magnetically, I wouldn't expect there to be much evidence forthcoming to support this idea.

As to birds... why would they need a special organ to indicate north-south when their eyes can do the job nicely?

[dsm]

Originally posted by DrChinese

There is a lot of speculation about sharks, but I haven't seen any convincing arguments. Study has been minimal, and has not produced the expected results in many cases. Most evidence is anecdotal.


But still interesting:

http://www.elasmo-research.org/education/topics/b_strandings.htm
http://news.nationalgeographic.com/news/2002/06/0606_020606_shark4.html


As to birds... why would they need a special organ to indicate north-south when their eyes can do the job nicely?


Ummm. If we blindfold you, twirled you around, and dropped you off someplace new, could you determine north from south with just your (un-blindfolded) eyes? Also, given the air currents, cloud formations, bad weather at high altitudes, could you find your way to Capistrano every year by just "following your nose"?

I mean, there's "skeptical", but let's not be silly...

[DrChinese]

Originally posted by dsm

Ummm. If we blindfold you, twirled you around, and dropped you off someplace new, could you determine north from south with just your (un-blindfolded) eyes? Also, given the air currents, cloud formations, bad weather at high altitudes, could you find your way to Capistrano every year by just "following your nose"?

I mean, there's "skeptical", but let's not be silly...

Most years, I don't migrate.

But I was more referring to a bird's eyes than my nose. And birds probably migrate via multiple cues when you refer to migrating to a very specific spot.

At any rate, I challenge anyone to locate an authoritative (and generally accepted) source for any vertibrate with an organ capable of directly detecting the earth's magnetic field. I don't think there are any.

[dsm]

Originally posted by DrChinese
At any rate, I challenge anyone to locate an authoritative (and generally accepted) source for any vertibrate with an organ capable of directly detecting the earth's magnetic field. I don't think there are any.

How about this (http://www.unc.edu/depts/oceanweb/turtles/)...?

[subgenius]

They finally posted a link to the contents of the show:

http://www.pbs.org/wgbh/nova/magnetic/