evidence: It may even indicate the beginning of a field reversal – a "flip" between the north and south magnetic poles. I'm a physicist who studies the interaction between the planets and space. While the north magnetic pole moving a little bit isn't a big deal, a reversal could have a big impact on Earth's climate and our modern technology. But these reversals don't happen instantaneously. Instead, they occur over thousands of years. [...] The Earth's magnetic field reverses on time scales that vary between 100,000 to 1,000,000 years. Scientists can tell how often the magnetic field reverses by looking at volcanic rocks in the ocean.