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 being belched back out via volcanoes. Yet, somehow, a sequence of rocks in the Isua Supracrustal Belt in Greenland has survived the ravages of time thanks to its unique geology, situated on top of a thick continental plate like a life-raft amid an ocean of tectonic upheaval.
