[Damocles]

Originally Posted by 3DMaster

According to 'established' science. You don't actually think I accept much if anything at all from those hacks and outright fraudeurs and priests, do you? And the average is 50,000 years, which is one of the very few things that does come from the lot of them.

Huh?

http://news.nationalgeographic.com/n...hmagfield.html

According to Earth's geologic record, our planet's magnetic field flips, on average, about once every 200,000 years. The time between reversals varies widely, however. The last time Earth's magnetic field flipped was about 780,000 years ago.


"We hear the magnetic field today looks like it is decreasing and might reverse. What we don't hear is it is on a time scale of thousands of years," Glatzmaier said. "It's nothing we'll experience in our lifetime."

But several generations from now, humans just may witness a reversal. By then, Glatzmaier said, scientists will better understand the process and be prepared to cope with the effects.

http://en.wikipedia.org/wiki/Earth's_magnetic_field

Magnetic field reversals
Main article: geomagnetic reversal
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, referred to as the Brunhes-Matuyama reversal.

The mechanism responsible for geomagnetic reversals is not well understood. Some scientists have produced models for the core of the Earth wherein the magnetic field is only quasi-stable and the poles can spontaneously migrate from one orientation to the other over the course of a few hundred to a few thousand years. Other scientists propose that the geodynamo first turns itself off, either spontaneously or through some external action like a comet impact, and then restarts itself with the "North" pole pointing either North or South. When the "North" reappears in the opposite direction, we would interpret this as a reversal, whereas turning off and returning in the same direction is called a geomagnetic excursion.

At present, the overall geomagnetic field is becoming weaker at a rate which would, if it continues, cause the field to disappear, albeit temporarily, by about 3000-4000 AD. The rapid deterioration began at least 150 years ago and has accelerated in the past several years, with a total decrease of 10-15% over these 150 years. This change is within the normal range of variation, as shown by study of magnetic fields in rocks, and need not necessarily lead to a reversal

http://science.nasa.gov/headlines/y2...neticfield.htm

Sometimes the field completely flips. The north and the south poles swap places. Such reversals, recorded in the magnetism of ancient rocks, are unpredictable. They come at irregular intervals averaging about 300,000 years; the last one was 780,000 years ago. Are we overdue for another? No one knows.

Now how was this record determined?

http://pubs.usgs.gov/publications/text/developing.html

Magnetic striping and polar reversals
Beginning in the 1950s, scientists, using magnetic instruments (magnetometers) adapted from airborne devices developed during World War II to detect submarines, began recognizing odd magnetic variations across the ocean floor. This finding, though unexpected, was not entirely surprising because it was known that basalt -- the iron-rich, volcanic rock making up the ocean floor-- contains a strongly magnetic mineral (magnetite) and can locally distort compass readings. This distortion was recognized by Icelandic mariners as early as the late 18th century. More important, because the presence of magnetite gives the basalt measurable magnetic properties, these newly discovered magnetic variations provided another means to study the deep ocean floor.

A theoretical model of the formation of magnetic striping. New oceanic crust forming continuously at the crest of the mid-ocean ridge cools and becomes increasingly older as it moves away from the ridge crest with seafloor spreading (see text): a. the spreading ridge about 5 million years ago; b. about 2 to 3 million years ago; and c. present-day.
Early in the 20th century, paleomagnetists (those who study the Earth's ancient magnetic field) -- such as Bernard Brunhes in France (in 1906) and Motonari Matuyama in Japan (in the 1920s) -- recognized that rocks generally belong to two groups according to their magnetic properties. One group has so-called normal polarity, characterized by the magnetic minerals in the rock having the same polarity as that of the Earth's present magnetic field. This would result in the north end of the rock's "compass needle" pointing toward magnetic north. The other group, however, has reversed polarity, indicated by a polarity alignment opposite to that of the Earth's present magnetic field. In this case, the north end of the rock's compass needle would point south. How could this be? This answer lies in the magnetite in volcanic rock. Grains of magnetite -- behaving like little magnets -- can align themselves with the orientation of the Earth's magnetic field. When magma (molten rock containing minerals and gases) cools to form solid volcanic rock, the alignment of the magnetite grains is "locked in," recording the Earth's magnetic orientation or polarity (normal or reversed) at the time of cooling.

Magnetic striping in the Pacific Northwest [70 k]
As more and more of the seafloor was mapped during the 1950s, the magnetic variations turned out not to be random or isolated occurrences, but instead revealed recognizable patterns. When these magnetic patterns were mapped over a wide region, the ocean floor showed a zebra-like pattern. Alternating stripes of magnetically different rock were laid out in rows on either side of the mid-ocean ridge: one stripe with normal polarity and the adjoining stripe with reversed polarity. The overall pattern, defined by these alternating bands of normally and reversely polarized rock, became known as magnetic striping.

And just for fun.........(Read on, you are going to love this! D.)

End of Part 1