In 1600, William Gilbert published a paper detailing how Earth behaves as a giant magnet. That seems like a long time ago, but in geologic time, that's nothing. It's taken hundreds of years to understand how the field works... but now that we do, scientists are trying to find hints from Earth's history that might reveal the future of this ever-changing invisible field all around us.
Scientists believe Earth's magnetic field is generated by the spinning of the Earth's core. Our planet's magnetic field is super important, as it blocks harmful rays emanating out of the sun from hitting us on the ground, destroying the possibility of life as we know it. It's always around us, and it strengthens and weakens over time -- sometimes, it even flips. We know the magnetic field has flipped, because there's evidence in the geologic record.
Now, a paper published in the Proceedings of the National Academy of Sciences in February 2017, found a way to enhance this hypothetical image by using ancient pottery. Clay is also subject to the same Earth's magnetic field record keeping, but the dates are far more precise.
NY Times: Ancient Jars Hold Clues About Earth's Fluctuating Magnetic Fields
LiveScience: Why Earth's Inner and Outer Cores Rotate in Opposite Directions
Washington Post: You might still be a simple bacterium, if not for magnetism