"183 reversals over the last 83 million years... A brief complete reversal, known as the Laschamp event, occurred only 41,000 years ago during the last glacial period. ... Geologists first noticed that some volcanic rocks were magnetized opposite to the direction of the local Earth's field.".
Here's a gif from a 1995 supercomputer simulation of the reversal process - https://imgur.com/a/jgpZZBF
"The tubes represent magnetic field lines, blue when the field points towards the center and yellow when away."
Indeed. Some people believe these “unshielded” periods might had some influence on the evolution of the species. Without those, the rate of change is just not enough to get to humans...
"183 reversals over the last 83 million years... A brief complete reversal, known as the Laschamp event, occurred only 41,000 years ago during the last glacial period. ... Geologists first noticed that some volcanic rocks were magnetized opposite to the direction of the local Earth's field.".