The magnetic field of the earth is generated by the dynamo action of liquid metal in the earth’s interior.

• The Riga Dynamo Experiment
  • “In November1999 a slowly growing magnetic field eigenmode was observed for the first time in a liquid metal experiment.”
  • http://dx.doi.org/10.1023/A:1024851818821
  • https://www.hzdr.de/db/Cms?pOid=14142&pNid=0&pLang=en
• Generation of a Magnetic Field by Dynamo Action in a Turbulent Flow of Liquid Sodium
  • “We report the observation of dynamo action in the von Kármán sodium experiment, i.e., the generation of a magnetic field by a strongly turbulent swirling flow of liquid sodium.”
  • https://doi.org/10.1103/PhysRevLett.98.044502
• The von Kármán Sodium experiment: Turbulent dynamical dynamos
  • “We first report observations related to the self-generation of a stationary dynamo when the flow forcing is ℛ𝜋-symmetric, i.e., when the impellers rotate in opposite directions at equal angular velocities.”
  • https://doi.org/10.1063/1.3085724
• Geomagnetic Dynamo: A Laboratory Model
  • “A mechanical model of a homogeneous self-maintaining dynamo was devised which confirmed Herzenberg’s model of the earth’s magnetic field”
  • https://doi.org/10.1038/1981158a0