Short answers, pulled from the story.
Convection currents in the liquid outer core generate electric currents through a process known as the geodynamo. This system consists of molten iron and nickel alloys flowing continuously to create a self-sustaining feedback loop between current loops and magnetic fields.
The boundary where pressures balance called the magnetopause sits about 10 Earth radii away on the sunward side. The opposite side stretches beyond 200 Earth radii into a long magnetotail containing the plasmasphere and Van Allen radiation belts.
The most recent geomagnetic reversal occurred approximately 780,000 years ago and is known as the Brunhes-Matuyama reversal. Reversals happen nearly randomly with intervals ranging from less than 0.1 million years to as much as 50 million years.
In 1831 this pole sat near Cape Adelaide in the Boothia Peninsula before moving to coordinates near Resolute Bay by 2001. Movement rates reached up to 55 kilometers per year in 2003 while global westward drift occurs at roughly 0.2 degrees per year since around 1400 AD.
Carl Friedrich Gauss measured Earth's magnetic field strength for the first time in 1832. Modern measurement relies on satellites like Ørsted and CHAMP alongside ground-based observatories that record data from over 100 interlinked stations worldwide since 1991.