evidence: In a study published today in Science Advances, researchers report a new estimated timeline of the last polarity reversal, named the Brunhes-Matuyama reversal, which happened around 780,000 years ago. Using a combination of lava samples, ocean sediments and ice cores, they were able to track the progression of this reversal and demonstrate that its pattern was longer and more complex than suggested by previous models. The findings could enable better understanding of how our planet’s magnetic environment evolves and hopefully guide predictions for the next major disturbance. "[Polarity reversal] is one of the few geophysical phenomena that is truly global," says Brad Singer, professor of geoscience at the University of Wisconsin–Madison and lead author of the study. "It’s a process that gets started in the deepest parts of the Earth, but it manifests itself in rocks across the entire surface of the planet and effects the atmosphere in pretty important ways. … If we can establish chronology for the timing of reversals, we have markers that we can use to date rocks all over the planet and know common time points around the entire Earth." [...] Over the last 2.6 million years, Earth’s magnetic field flipped 10 times and nearly flipped more than 20 times during events called excursions. Some researchers believe polarity reversals are caused by a disturbance in the balance between Earth’s rotation and the temperature at the core, which alters the fluid motion of the liquid iron, but the exact process remains a mystery.