Magnetic field: invisible shield that keeps air
Powered by liquid iron 2900 kilometers down, the shield deflects solar wind and last flipped 780000 years ago.
Liquid iron dynamo makes the shield
About 2900 kilometers down liquid iron churns at 5000 degrees, spinning with Earth to generate electric currents. This dynamo builds a magnetosphere reaching 10 Earth radii sunward that deflects supersonic solar wind around our planet.
Without this shield solar wind would strip air like it stripped Mars 4 billion years ago. Mars lost its global field and then 90 percent of air, turning wet valleys into desert while Earth kept thick nitrogen oxygen atmosphere.
Auroras glow and poles sometimes flip
Charged particles slide to poles and strike air 100 to 300 kilometers high, painting green oxygen and red nitrogen auroras. During strong storms in 1859 and 2024 auroras reached tropics while currents surged in power grids.
Rocks show field flips every 200000 to 300000 years on average, last reversal 780000 years ago. A flip takes 1000 to 10000 years with weaker shield and more auroras, but air stays because gravity holds gases even when compasses wander.
- Source: liquid iron outer core at 2900 kilometers
- Size: 10 Earth radii sunward, tail 200 radii
- Mars lost air after field died 4 billion years ago
- Auroras at 100 to 300 kilometers altitude
- Flips every 200000 years, last 780000 years ago