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The polarity reversal was a global event. © Dr. habil. Norbert R. Nowaczyk / GFZ 41,000 years ago, a complete and rapid reversal of the geomagnetic field occured. Magnetic studies of the GFZ German Research Centre for Geosciences on sediment cores from the Black Sea show that during this period, during the last ice age, a compass at the Black Sea would have pointed to the south instead of north. Moreover, data obtained by the research team formed around GFZ researchers Dr. Norbert Nowaczyk and Prof. Helge Arz, together with additional data from other studies in the North Atlantic, the South Pacific and Hawaii, prove that this polarity reversal was a global event. Their results are published in the latest issue of the scientific journal Earth and Planetary Science Letters. What is remarkable is the speed of the reversal: "The field geometry of reversed polarity, with field lines pointing into the opposite direction when compared to today's configuration, lasted for only about 440 years, and it was associated with a field strength that was only one quarter of today's field," explains Norbert Nowaczyk. "The actual polarity changes lasted only 250 years. In terms of geological time scales, that is very fast." During this period, the field was even weaker, with only 5% of today's field strength. As a consequence, the Earth nearly completely lost its protection shield against hard cosmic rays, leading to a significantly increased radiation exposure. Read more at: phys.org...
The first time evidence was discovered of a rapid geomagnetic field reversal was in 1995 when well-preserved lava flows were found at Steens Mountain in Oregon in the US. Research on the rocks by a team led by geologist Scott Bogue of the Occidental College in Los Angeles revealed the lava flow had an unusual magnetic pattern that suggested the magnetic field had been shifting over 10,000 times faster than normal, at six degrees a day. The magnetic patterns are preserved within the magnetic crystals in the lava, formed as the lava flow cooled. The first findings remained controversial and many scientists have challenged the fast flip-flop theory, but now Bogue and colleague Jonathan Glen of the US Geological Survey have found evidence in ancient lava rock in Battle Mountain, Nevada of a second fast flip, dated around 15 million years ago. The record in one particular lava flow in Nevada suggests the magnetic field moved by 53 degrees in a single year.
Read more at: phys.org...