I pose a serious question and get flamed! boy what new around here with some of you A holes I.E. (Dowding the butt pirate!)
Dowding you've been igonred and the to i say "you've been served!"
to start here is just one source of info on the magnetic field stuff!
http://www.newscientist.com/news/news.jsp?id=ns99994865the articale reads..............
The World's No.1 Science & Technology News Service
Quick flip of Earth's magnetic field revealed
18:00 07 April 04
NewScientist.com news service
The Earth's magnetic field takes an average of only 7000 years to reverse its polarity, but the switch happens much more quickly near the equator, according to the most comprehensive study yet of the last four reversals.
"It's important to get an idea of how fast or slow this process is because it ends up controlling our idea of how the field is generated in the first place," says study author Bradford Clement, an earth scientist at Florida International University in Miami, US.
Previous studies have reported a bewildering range of transition times, from a few thousand to nearly 30,000 years. So Clement scoured the published data on the most recent reversals to set the record straight.
He used data from 30 cores drilled from the beds of lakes or seas, whose minerals clearly recorded the magnetic field as sediments in the water slowly solidified into rock. The cores were taken from latitudes ranging from 46 degrees south to 60 degrees north and from a wide range of longitudes.
Clement found that the duration of the transitions varied with latitude, from 2000 years near the equator to 11,000 years nearer the poles. This result concurs with a much smaller study he conducted 20 years ago using just 10 cores.
"Now the data set looks more robust overall, and the variation with latitude helps explain why people were reporting different durations," Clement told New Scientist.
Random timing
Studies of ocean sediments and lava flows show the Earth has undergone several hundred field reversals, with the most recent confirmed flip occurring about 780,000 years ago. But their timing appears random and physicists do not understand what causes them.
The Earth's magnetic field is generated by the flow of liquid iron, an electrical conductor, in the Earth's outer core, between 3000 and 5000 kilometres beneath the surface. It is therefore likely that some change in the flow causes the reversals.
But the many models put forward to explain the phenomenon are "a long way from being realistic", says Clement. "The theory gets very complicated very quickly, and there are so many models it's hard to figure out what's what."
Ronald Merrill, a geophysicist at the University of Washington, in Seattle, US, agrees: "We can't do the theory right, so we're trying to find more data to find out the character of the reversals."
Shrinking magnet
Merrill says better knowledge of the reversals will help constrain the many models. And it may even shed light on some evidence published in 2002 suggesting that the Earth is now in the first stages of a polarity flip.
In the simplest models of reversals, the Earth's magnetic field behaves like a bar magnet that points roughly along the planet's axis of rotation. It shrinks in strength over time, growing up again in the opposite direction.
Clement's result "tells us the magnetic field is becoming more complex during a reversal," says Merrill. This could occur if secondary components of the magnetic field - perhaps caused by eddies of molten iron at shallower depths - remain constant as the primary field - caused by iron flowing deep in the outer core - shrinks to nothing.
