The polarity switch, also known as a geomagnetic reversal, is a change into the Earth's magnetic field in which the magnetic poles are interchanged. Thus, after such a flip, the geographic north will correspond with a magnetic sound and vice-versa.
This is a process that occurs approximately every 200 to 300 thousand years, although exceptions occur. The evidence of this process is obtained by the stratgraphy, a branc of geology studying the relationship between strata and geological timescale.
A Geomagnetic Polarity Time Scale has been obtained through the analysis of seafloor magnetic anomalies and the dating of reversal sequences on land. Thus, sediment cores taken from deep ocean floors can provide a direct link between magnetic field activity and fossil record.
Another proof of this process is the volcanic lava that when solidifying, it is magnetized by the Earth's magnetic field and thus records its orientation.
