The motion of Earth\u2019s magnetic poles, through geological time, over the surface of Earth. It has been standard fare in physics textbooks for scores of years to describe a movement of Earth\u2019s magnetic poles around Earth\u2019s axis of rotation. For example, S. G. Starling in Electricity and Magnetism (1912) explains that the magnetic North Pole describes a circle of 17\u00b0 radius around the axis in about 960 years.<\/p>\n
That, however, turns out to be a relatively minor polar shift. In the last 50 years the science of paleomagnetism the study of magnetized rocks has advanced dramatically. At the time rocks are laid down, they are very weakly magnetized by Earths magnetic held. The direction and strength of their magnetization provides a record of Earth\u2019s held at the time and place that they were laid down. If the poles had remained about where they are now, as described above, we should expect the record to show a magnetic held roughly pointing north with the north, north, and the south, south. That turns out not to be so. Rocks can be dated accurately over the last 5 million years, and they show complete polar reversals about 25 times in that period. The North and South Poles change places, abruptly in geological terms, they hip over in about 1,000 to 10,000 years. The changeovers are very erratic: steady as we now are for the last 800,000 years and then six hips in the preceding million years and that irregular pattern is typical.<\/p>\n
<\/p>\n","protected":false},"excerpt":{"rendered":"
The motion of Earth\u2019s magnetic poles, through geological time, over the surface of Earth. It has been standard fare in physics textbooks for scores of years to describe a movement of Earth\u2019s magnetic poles around Earth\u2019s axis of rotation. For example, S. G. Starling in Electricity and Magnetism (1912) explains that the magnetic North Pole […]<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[16],"tags":[],"class_list":["post-211223","post","type-post","status-publish","format-standard","hentry","category-p"],"yoast_head":"\n