Is Earth’s magnetic field crucial to the planet’s habitability? Did it enable the evolution of life? Scientists have pondered those questions for at least 60 years.1 The geomagnetic field shields our planet from solar and cosmic radiation that are harmful to life. The magnetosphere, illustrated in figure 1, can limit erosion of the atmosphere by solar winds. And it helps keep water, an essential ingredient for life as we know it, from escaping to space. Based on those facts, many scientists view evidence for the great antiquity of the geodynamo—which is thought to be more than 4 billion years old2—as consonant with a geomagnetic field that has helped preserve Earth’s oceans and habitability. But those who study the core, dynamo, and magnetism have found questions about their relationship to life ever more intriguing as new findings have shifted our understanding of ancient Earth.
The magnetic field...
