earth's magnetic field is produced by what?
the standard explanation is the Dynamo theory
"Dynamo theory proposes a mechanism by which a celestial body such as the earth generates a magnetic field. In the case of the earth the magnetic field is believed to be caused by the convection of molten iron and nickel, within the planetary core, along with the overall planetary rotation. This results in the creation of electric currents as well as a magnetic field."
though, like is habitual in science, there are alternative hypothesis
On the origin of the Earth's magnetic field
Authors: Gregory Ryskin
Comments: 11 pages
"It is thought that the magnetic field of the Earth is generated by the hydromagnetic dynamo action in the Earth's liquid outer core, consisting mainly of iron (the standard model). Here I propose that the magnetic field of the Earth is generated by dynamo action in the world ocean at the Earth's surface. This hypothesis is free of the problems of the standard model; in particular, it explains the close temporal correlation between geomagnetic reversals and the stratigraphic boundaries defined by major or minor mass extinctions. Implications of this hypothesis for other terrestrial planets are briefly discussed."
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