The Real Science Behind the Excursion
In the world of Gideon Irondell, civilization was reshaped by an event called the Great Excursion — a magnetic pole reversal that split the world into Zetash and Uunders. That premise isn’t pure invention. Earth’s magnetic field really does this. Here’s what we actually know.
- Earth’s magnetic field has flipped polarity roughly 183 times in the last 83 million years — we know this from magnetic striping frozen into the seafloor as it forms, which was also one of the key pieces of evidence that confirmed plate tectonics.
- The most recent full reversal, called the Brunhes–Matuyama reversal, happened about 780,000 years ago.
- Reversals don’t run on a predictable schedule. Gaps between them have ranged from tens of thousands of years to, in one stretch, over 30 million years with no reversal at all.
- A reversal isn’t instant — it plays out over anywhere from a couple hundred to several thousand years, depending on the event and how it’s measured.
- Mid-reversal, the field doesn’t cleanly rotate. It gets messy and multipolar, with several weak north and south regions appearing before settling into a single new orientation — and it also weakens dramatically, dropping by as much as 90% of normal strength at the low point.
- Not every disruption is a full reversal. Earth’s last complete pole flip was 780,000 years ago — but a partial, temporary event called the Laschamp Excursion happened far more recently: just 41,000 years ago. The field weakened to near-collapse, wandered, and then recovered without ever fully reversing.
- During the Laschamp Excursion, field strength dropped to roughly 5–10% of today’s levels, the field briefly became multipolar (researchers have compared it to the messier magnetic fields seen on planets like Uranus or Neptune), and auroras were spotted far outside their normal range — as far as near-equatorial latitudes, somewhere they’re essentially never visible today.
- With Earth’s shield down during Laschamp, cosmic ray exposure roughly doubled — measurable today in ice cores from Greenland and Antarctica.
- Some researchers connect the Laschamp event to behavioral shifts in early humans living in Europe at the time — more cave use, tailored clothing, and wider use of ochre (which has UV-protective properties) have all been proposed as adaptive responses. It’s also been floated as a contributing factor in the Neanderthal extinction timeline, though climate and competition with Homo sapiens are considered the bigger drivers.
- We are not currently mid-reversal, but Earth’s field has weakened by about 9% over the last 170-odd years, and there’s a region called the South Atlantic Anomaly where field strength is unusually low right now.
- Despite popular assumption, there’s no solid scientific evidence linking past reversals to mass extinctions — the correlation researchers look for in the fossil record is weak and contested.
- The field itself comes from the geodynamo — churning, convecting liquid iron in Earth’s outer core, roughly 1,800 miles down. Not a bar magnet. A planet-sized engine.
The Gideon Irondell Trilogy imagines what might happen if a reversal reshaped human civilization instead of just its compasses. Book One, Gideon Irondell and the Magnet of Marjon, is available now.