Ancient rocks hold proof of Earth's magnetic field. Here's why that's puzzling – Space.com

Ancient rocks hold proof of Earth’s magnetic field. Here’s why that’s puzzling  Space.com Earth’s magnetic field formed before the planet’s core, study suggests  Livescience.com Researchers find oldest undisputed evidence of Earth’s magnetic field  Phys.org Scientists uncover 3.7-billion-year-old record of Earth’s magnetic field  Interesting Engineering…