When did the Earth's magnetic poles last reverse?
When did the Earth's magnetic poles last reverse?
About 780,000 years ago
The Brunhes–Matuyama reversal
Reversals happen irregularly, on average every few hundred thousand years, and the record is written into the ocean floor: new crust forming at mid-ocean ridges locks in the field direction as it cools, producing symmetrical magnetic stripes either side of the ridge. That pattern was the decisive evidence for plate tectonics. The field has weakened by around nine per cent since measurements began in 1840, which is sometimes reported as an imminent reversal and is well within normal variation.
- What
- The Brunhes–Matuyama reversal
- When
- About 780,000 years ago
- Category
- The natural world
- Could this change?
- Not in any foreseeable way. The event is closed.
The natural world
| Question | When |
|---|---|
| When did Vesuvius last erupt? | March 1944 |
| When did the last thylacine die? | 7 September 1936 |
| When did the last passenger pigeon die? | 1 September 1914 |
| When did the last ice age end? | About 11,700 years ago |
This page gives a date and never a "years ago". These pages are built as static files, so a computed interval would freeze at build time and quietly become wrong — which on a reference site is worse than making the reader do the subtraction.
Common questions
- When did the Earth's magnetic poles last reverse?
- About 780,000 years ago — The Brunhes–Matuyama reversal.
- What happened?
- Reversals happen irregularly, on average every few hundred thousand years, and the record is written into the ocean floor: new crust forming at mid-ocean ridges locks in the field direction as it cools, producing symmetrical magnetic stripes either side of the ridge. That pattern was the decisive evidence for plate tectonics. The field has weakened by around nine per cent since measurements began in 1840, which is sometimes reported as an imminent reversal and is well within normal variation.
Related pages
- When did Vesuvius last erupt? March 1944
- When did the last thylacine die? 7 September 1936
- When did the last passenger pigeon die? 1 September 1914
- When did the last ice age end? About 11,700 years ago
- Everything, most recent first 36 last occurrences
Sources
- United States Geological Survey — USGS (Public domain (US Government))