According to researchers from Japan and the USA, the latest reversal of the geomagnetic field of the earth took around 22,000 years. The researchers came to the result through finding derived by sedimentary, volcanic, and ice-core records. As per the results, the reversal can take a longer time than it was previously assumed. The geomagnetic field formed by motion of outer core of the earth, that acts as a dynamo. The geomagnetic field is stable, but it may change with time. For example, the North pole is moving towards Siberia, the field strength is decreasing by about 5% each century.
Minerals in some of the rocks provide information related to the magnetic field that were formed. According to Brad Singer a geologist at the University of Wisconsin Madison, the reversals are formed in the seep parts of the interior of the earth. It is unclear what impact the upcoming reversal have on navigation, humans, and communication. Brad Singer along with his colleagues took magnetic readings of rock samples from Canary Islands, Chile, the Caribbean, Tahiti, and Hawaii to develop an accurate picture. The researchers determined the age of rocks using potassium-argon radioisotope method. As per Singer, the lava flows provide accurate information of the magnetic field. Lava has iron-bearing minerals and they get locked in the field direction when they get cool.
The team of researchers compared the results of lava flows with other sources of data. The magnetic readings were first taken from the seafloor, which provides data with low accuracy as compared to lava flow due to weaker magnetization, variation in sediment rates, and others biological disruption. The other source of data was from beryllium deposits preserved in cores of Antarctic. The beryllium is formed when cosmos rays hits the atmosphere, which allows large amount of radiation to pass when the magnetic field is weak. Mr. Brad Singer and his colleagues found that the reversal of the earth had taken less than 4,000 years, rapidly as per geological standards.