Pole reversal · Observatoire des phénomènes naturels

Poles · reversal

When north turns south

About 780,000 years ago the Earth’s magnetic field reversed (Matuyama–Brunhes). The animation replays the GGFMB model every 50 years from 900,000 to 700,000 years ago: the dipole axis tips over and the moment collapses during the transition.

Age: —
Polarity: —
Dipole moment: —

Normal polarity
Reversed polarity

Last reversal

≈ 780 ka

transition interpreted at 799–770 ka

Transition length

a few thousand years

from published reconstructions

Model

GGFMB

Mahgoub et al. (2023)

Mahgoub et al. (2023) · Published literature; cited

Dipole reconstructed by the GGFMB model (g10, g11, h11); field lines of a pure dipole, length from the moment. A reconstruction, not a direct measurement.

08 / DEEP TIME · GGFMB

The last magnetic reversal

A separate reconstruction of the global magnetic field, 900,000–700,000 years ago. Explore the signed axial dipole as the field changed polarity.

MODEL AGE780 ka BP

POLARITY—

AXIAL DIPOLE g₁⁰—µT

DIPOLE MOMENT—× 10²² A·m²

09 / FIELD STRENGTH

Dipole moment through the reversal

The same GGFMB epochs, in 10²² A·m². A weak field accompanies the polarity transition.

The shaded 799–770 ka interval is the authors' approximate reversal window. GGFMB is a model from sediment records; during transition the field is complex, so a single north/south pole path would be misleading.

Independent evidence: beryllium-10

Marine sediment records show increased cosmogenic ¹⁰Be production around the Matuyama–Brunhes transition as the dipole weakened. Their age models and sampling differ from GGFMB, so no point-by-point correlation is implied here.

Read the sediment study ↗

10 / POLARITY TIMESCALE

Reversals over 3.6 million years

Normal (light) and reversed (dark) polarity from the GTS2012 timescale, with two dated excursions. The bracket marks the 900–700 ka GGFMB window above.

IODP, Table T11 (GTS2012 ages) ↗Ogg (2012), GTS2012 ↗Excursion ages ↗

GGFMB data ↗Scientific paper ↗

SOURCES OF THIS PAGE

Mahgoub et al. (2023): Mahgoub, A. N., Korte, M., & Panovska, S. (2023). Characteristics of the Matuyama–Brunhes magnetic field reversal based on a global data compilation. Journal of Geophysical Research: Solid Earth, 128, e2023JB026593. · doi:10.1029/2023JB026593
Licence : Published literature; cited

Pole reversal GGFMB model of the Matuyama–Brunhes reversal, 900–700 ka

When north turns south

The last magnetic reversal

Dipole moment through the reversal

Reversals over 3.6 million years