Earth's magnetic field switches on
A dynamo starts turning in the molten core, raising the shield that still deflects the solar wind.
- When
- Known to
- ± 150 million years
- Era
- Hadean
Magnetite trapped in Jack Hills zircons appears to record a geomagnetic field as far back as 4.2 billion years, only a few hundred million years after the Moon-forming impact. An early field would have protected the young atmosphere and any nascent life from being stripped away by the solar wind. The evidence is contested — the magnetite may have entered the crystals long after they formed — and the origin of the field remains genuinely open.