Tag: proof

Ancient rocks hold proof of Earth’s magnetic field. Here’s why that’s puzzling

A 3.7-billion-year-old record of our planet’s ancient magnetism has been unearthed, providing evidence that Earth’s magnetic field already existed very early in history. This discovery, however, is quite surprising. Rocks approaching 4 billion years old are hard to find; most have been recycled through Earth‘s tectonic activity, slipping into the mantle through subduction zones before […]