evidence: Earth's magnetic field has flipped many times over the last billion years, according to the geologic record. But only in the past decade have scientists developed and evolved a computer model to demonstrate how these reversals occur. [...] Our planet's magnetic field reverses about once every 200,000 years on average. However, the time between reversals is highly variable. The last time Earth's magnetic field flipped was 780,000 years ago, according to the geologic record of Earth's polarity. [...] These bits of a pole reversal are referred to as instabilities. They constantly occur in the fluid flow of the core, tracking through it like little hurricanes, though at a much slower pace—about one degree of latitude per year.