Earth's Magnetic Reversal

Thought that this may interest people keeping their eye on the solar-system and such...

Magnetic Reversals
After molten lava emerges from a volcano, it solidifies to a rock. In most cases it is a black rock known as basalt, which is faintly magnetic, like iron emerging from a melt--for which Gilbert already noticed a similar process. Its magnetization is in the direction of the local magnetic force at the time when it cools down.

Instruments can measure the magnetization of basalt. Therefore, if a volcano has produced many lava flows over a past period, scientists can analyze the magnetizations of the various flows and from them get an idea on how the direction of the local Earth's field varied in the past. Surprisingly, this procedure suggested that times existed when the magnetization had the opposite direction from today's. All sorts of explanation were proposed, but in the end the only one which passed all tests was that in the distant past, indeed, the magnetic polarity of the Earth was sometimes reversed.

Please Note: This web site regularly receives questions about reversals. Do they pose a danger to life on Earth? Is one due soon? How quickly do they take place? Click here to bring up four of those questions, with their answers.

Found it from NASA site... http://istp.gsfc.nasa.gov/earthmag/reversal.htmhttp://istp.gsfc.nasa.gov/earthmag/reversal.htm

From this NASA site: http://science.nasa.gov/science-news/science-at-nasa/2001/ast15feb_1/


http://science.nasa.gov/science-news/science-at-nasa/2001/ast15feb_1/