Geomagnetic polarity dating
Most reversals take between 1,000 and 10,000 years to happen.
The North geomagnetic pole, located near Greenland in the northern hemisphere, is actually the south pole of the Earth's magnetic field, and the South geomagnetic pole is the north pole.However, at irregular intervals averaging several hundred thousand years, the Earth's field reverses and the North and South Magnetic Poles relatively abruptly switch places.These reversals of the geomagnetic poles leave a record in rocks that are of value to paleomagnetists in calculating geomagnetic fields in the past.Statistical analysis shows no evidence for a correlation between reversals and extinctions.The lines represent magnetic field lines, blue when the field points towards the center and yellow when away.This convection (movement) generates electric currents which in turn give rise to magnetic fields.
In simulations of planetary dynamos, reversals occur from the underlying dynamics.
A brief complete reversal, known as the Laschamp event, occurred only 41,000 years ago during the last glacial period.
That reversal lasted only about 440 years with the actual change of polarity lasting around 250 years.
Data is got by towing a magnetometer along the sea floor.
No existing unsubducted sea floor is more than about 180 million years old, so other methods are used for detecting older reversals.
Geomagnetic polarity during the last 5 million years (Pliocene and Quaternary, late Cainozoic era).