What is the pattern of magnetic polarity reversals?

Answer 1

In a geomagnetic reversal, the south and north magnetic poles flip locations. A magnetic pole reversal takes place every 450,000 years on average, but this is not regular. We are way overdue since the last reversal was 780,000 years ago. There is a pattern in the magnetic polarity of basaltic rocks on opposite sides of a mid-ocean ridge. Basalt contains tiny magnetic crystals that point to the location of the north magnetic pole at the time the lava cools. The rocks at the ridge have positive polarity, but on either side of the ridge the polarity is negative, indicating that those lavas cooled when the magnetic field was opposite of what it is today. On either side of the basalt with negative polarity are more rocks with positive polarity. This pattern continues on both sides of the mid-ocean ridge across the ocean basin. The pattern of magnetic polarity is one of the main lines of evidence for seafloor spreading, which is the mechanism for plate tectonics.