1. A moving conductor rather than a permanently magnetized iron lump

The dynamo responsible for Earth's main magnetic field links motion of liquid metal in the outer core to electric currents. NASA explains that convection and flows organized by Earth's rotation generate currents and maintain the field. This differs from placing a permanently magnetized bar of iron at Earth's center.

Convection is fluid motion transporting heat; rotation affects the direction and structure of that motion. Saying that Earth becomes a magnet simply because it spins skips essential steps. Motion of an electrically conducting fluid and field generation must work together.

2. What a model reproduced versus what was observed

A 1995 report by Glatzmaier, Hollerbach and Roberts describes a model jointly calculating convection and magnetic-field generation in a rotating, three-dimensional spherical fluid shell. It calculates physical processes rather than directly imaging the outer core.

UCSC's account of Earth scientist Gary Glatzmaier's explanation distinguishes the model's Earthlike field and polarity reversals from lower confidence in details. These comments concern the modeling research as described in 2000. One simulated reversal does not date Earth's next actual reversal.

Satellites and ground observatories measure the present field's strength and direction; magnetic records preserved in rocks and other materials provide indirect evidence of past directions. Models supply physical explanations to compare with those records. Measurements, historical indirect evidence and calculations should not be treated as interchangeable evidence.

3. Read numbers before colors on a magnetic map

NASA presents Swarm maps of average field strength and its change during January–June 2014. The change map also uses vivid colors, yet its largest changes are about ±100 nT, while the strength map reaches 60,000 nT. Similar colors do not mean that the change is as large as the total field. These figures describe those historical maps, not today's values.

Check whether a map shows strength or change, its units and color scale, and its averaging period. A regional weakening or a moving magnetic pole alone does not establish a global polarity reversal. NASA distinguishes pole movement from reversals, whose intervals vary widely. An average interval cannot serve as a regular countdown.

4. Sources

The 1995 research report: numerical modeling of convection and field generation. UCSC: Glatzmaier's research explanation and limits on model details. NASA: the outer-core dynamo, observational records and field-map interpretation.