The Earth's magnetic field reverses its polarity from time to time doesn't it?

When do we expect it to reverse again? (I'd really hate to miss it ) What are the consequences?

From frankvan's link above:

quote:

The Earth's magnetic field reverses at intervals, ranging from tens of thousands to many millions of years, with an average interval of approximately 250,000 years. It is believed that this last occurred some 780,000 years ago,

One of the consequences is that, during the period of reversal (though the mechanism is not well understood), the magnetic field surrounding the earth diminishes. This allows charged particles of the solar wind to more readily reach the earth's surface, instead of being deflected by the magnetic field as they normally are. This in turn might be harmful to all living things. But I'm not going to start worrying about it for at least another 10,000 years.

I heard that it reverses every 10 000 to 1 000 000 year - no sure if this is true or not.

quote:

Originally posted by Matiqua:
I heard that it reverses every 10 000 to 1 000 000 year - no sure if this is true or not.

Whether you use your figures or the one I quoted above, that's quite a range -- varying by a factor of one hundred or more. I did a little more digging on Google and discovered that it is indeed a poorly understood and poorly documented phenomenon. However Space Daily reported on a publication in Nature (April, 2004) that claims:

Earth's magnetic field reverses every few thousand years at low latitudes and every 10,000 years at high latitudes, a geologist funded by the National Science Foundation (NSF) has concluded. Brad Clement of Florida International University published his findings in this week's issue of the journal Nature. The results are a major step forward in scientists' understanding of how Earth's magnetic field works.

It goes on to say:

quote:

Since the time of Albert Einstein, researchers have tried to nail down a firm time-frame during which reversals of Earth's magnetic field occur.

So I don't think an answer to FredPuli's original question is readily forthcoming.

DG -- why don't you see if you can genetically engineer a tomato that produces its own internal magnetic field. Maybe you could market it as both safe from cosmic rays and uncommonly rich in iron.

I think the best explanation for the presence of the earth's magnetic field is the movement of liquid within the earth's core. A great deal of the earth's make-up is ferrous metals, which are magnetic.

If you place differences of voltage potential at either end of a wire, you get current. But you also get a magnetic field around the wire. As the current moves, the field moves with it. With alternating current, the field collapses and expands.

The opposite is also true, if you move the magnetic field, you induce current in the wire. So when the movement of liquid metals in the earth's core reverses or changes direction, the magnetic field we measure on the surface changes.

We move about on the surface without ever noticing the field, or the thousands of other man-made disturbances in the air, radio waves. The affect of the field would depend on frequency, no doubt, and at most frequencies, we are oblivious.

(The earth's magnetic field has actually been mapped out. Field strengths at all points on the surface are fed into navigation computers for use in anti-mine systems on board blue-water vessels. A metal ship moving through the water cuts across the earth's magnetic field, and magnetic mines are designed to sense the change. On a ship, a degausing system reads the ship's changes in potential and negates them, causing the ship to have no magnetic signature regardless of direction or speed.)

It is true that much of the Earth is molten iron, but molten iron is not magnetic. Iron's ferromagnatic nature does not appear to have much to do with it. (I believe ferromagnetic is what was meant, since ferrous is a certain state of iron, does not apply to other substances, and is unrelated to magnetism)

It is also not quite so simple as moving metal because there needs to be a moving charge to produce a magnetic field. It is believed that friction creates this charge.