Earth's Core Dynamo Generates a Sustained Magnetic Field

By 3.7 billion years ago, Earth's liquid iron outer core was generating a sustained magnetic field through convection-driven dynamo action. Paleomagnetic analysis of iron oxide minerals in the Isua Supracrustal Belt of Greenland reveals a field strength of at least 15 microtesla, roughly half the modern value. The resulting magnetosphere deflected solar wind that would otherwise strip atmospheric gases. Mars, which lost its dynamo around this period, subsequently lost most of its atmosphere and surface water. Contested zircon evidence from Jack Hills, Australia, suggests the dynamo may have activated as early as 4.2 billion years ago.