Resumen de Earth's ghostly guardian
Woo talks about the Earth's protective magnetic field, a force field whose source lies in the churning molten iron that forms the planet's core. Electrons flowing through this fluid generate an electric current, which in turn creates a magnetic field. The core is a giant, self-sustaining electromagnet: a dynamo. But over the last few years, evidence is mounting that the dynamo could only have emerged comparatively recently. At the same time, geological clues show that the magnetic field has existed for most of Earth's 4.5-billion-year history. This contradiction--an ancient magnetic field without anything to power it--is forcing people to rethink their planet's insides.
