The iron catastrophe
Iron sinks inward and gives Earth a magnetic shield
See it on the timeline →In depth
Differentiation released so much gravitational energy that it heated the planet further — hence the name. The result is a liquid outer core of iron and nickel that acts as a dynamo and generates the magnetic field. The magnetosphere deflects the solar wind, which would otherwise strip the atmosphere away over time. Mars probably lost its magnetic field around four billion years ago, and with it most of its air and water. The difference between a living planet and a dead one may come down to how well the core holds its heat.
For children
The young Earth was so hot it was liquid. All the heavy iron sank inward toward the middle, like lumps settling in a pot, and formed a core. That core is still spinning, and it makes an invisible magnetic field around the whole planet that shields us from dangerous radiation from the Sun.
Connects to
Part of Terra Saga — the story of Earth on a timeline. terrasaga.org