The geomagnetic field, generated in the liquid outer core, provides a shield from cosmic radiation that can cause damage to man-made satellites, electrical power grids, and the ozone layer (1). In the absence of this shield, the solar wind might gradually erode the atmosphere, eventually robbing the planet of its water (2). But the dipole magnetic field has decreased in strength over the last 160 y at an alarming rate (3), motivating continued spirited debate (4⇓–6) over whether we are in the early stages of a geomagnetic pole reversal. Some even believe we are overdue. But 160 y is just a blink of the eye in geological terms. The record is too short to have great confidence about what these trends might mean about causal processes and the future. In PNAS, Trindade et al. (7) provide insightful context for these modern changes in the form of a magnetic record from South America that extends ∼1,500 y into the past.
We know much about the recent waning geomagnetic field; since the time of Gauss in 1840, we have had a rich data source in the form of geomagnetic observatory records. In the satellite era, we have a deluge of data from magnetometers in orbit. From analyses of these data, we know that the field-intensity decrease is concentrated in an area known as the South Atlantic Anomaly (SAA), a vast swatch stretching from South Africa to Chile. Amazingly, when one estimates the field structure beneath this region at the core–mantle …
↵1Email: john.tarduno{at}rochester.edu.
