geomagnetic reversal

geomagnetic reversal
Name	Geomagnetic reversal
Field	Geophysics, Paleomagnetism
Notable examples	Brunhes–Matuyama reversal, Matuyama Chron, Jaramillo

Contents

geomagnetic reversal Geomagnetic reversal describes the change in orientation of Earth's magnetic field such that the positions of magnetic north and south are interchanged. The phenomenon is recorded in volcanic Mount Etna flows, marine Mid-Atlantic Ridge basalts, and sedimentary sequences correlated with the Brunhes–Matuyama reversal and the Matuyama Chron, informing studies by institutions such as the United States Geological Survey and the British Geological Survey. Research into reversals involves collaborations among scholars at Instituto Geofísico, Scripps Institution of Oceanography, Lamont–Doherty Earth Observatory, and agencies like NASA and the National Science Foundation.

Introduction

Geomagnetic reversals are global-scale events recognized in the stratigraphy of Paleocene–Eocene Thermal Maximum, Cretaceous Normal Superchron, and Pliocene sequences and tied to time scales used by the International Commission on Stratigraphy and the Geological Society of America. Early recognition stemmed from work by Bernhard Brunhes, Motonori Matuyama, and later synthesis by Keith Runcorn and Patrick M. Hurley, with mapping efforts linked to projects at Lamont–Doherty Earth Observatory and datasets curated by the National Oceanic and Atmospheric Administration. Reversals are distinguished from excursions documented in the Laschamp event and the Mono Lake excursion, and they are integrated into geomagnetic polarity time scales used by the International Association of Seismology and Physics of the Earth's Interior.

Reversal studies focus on the fluid-dynamical processes in Earth's outer core as described in models developed at Princeton University, École Normale Supérieure, Max Planck Institute for Solar System Research, and the University of Cambridge. The geodynamo is modeled via magnetohydrodynamics informed by the work of Walter M. Elsasser, Edward Bullard, and Olaf R. Phillips and implemented using numerical codes from groups at Los Alamos National Laboratory and the University of California, Berkeley. Mechanisms invoke convective overturn, rotational influence described by the Coriolis force, and magnetic diffusion constrained by parameters estimated from seismology groups at California Institute of Technology and Imperial College London. Reversals may initiate through instabilities analogous to behavior in dynamos studied at Dresden Technical University laboratories and compared to planetary dynamos of Jupiter, Saturn, and Mercury.

Primary evidence comes from thermoremanent magnetization in lavas from Hawaii Volcanoes National Park, Iceland, and Mount Etna, and from detrital remanent magnetization in sedimentary sections at Loess Plateau and Siwalik Hills. Marine magnetic anomalies over the Mid-Atlantic Ridge, East Pacific Rise, and Indian Ocean seafloor correlate with polarity chrons used by teams at Woods Hole Oceanographic Institution and the Scripps Institution of Oceanography. Laboratory techniques developed by researchers at ETH Zurich and University of Tokyo enable anisotropy corrections and paleointensity estimations tied to cores collected by the Integrated Ocean Drilling Program and the International Ocean Discovery Program.

Reversals exhibit variable frequency such as the long Cretaceous Normal Superchron and the rapid succession around the Matuyama–Brunhes transition studied by paleomagnetists at University of Oxford and University of Leeds. Statistical analyses using methods from Columbia University and Stanford University evaluate Poisson-like models, clustered waiting-time distributions, and power spectra that incorporate time scales defined by the International Chronostratigraphic Chart. Typical reversal durations range from thousands to hundreds of thousands of years, with polarity stability intervals mapped by teams at the Geological Survey of Canada and the Australian National University.

Investigations into biospheric impacts reference work linking solar and magnetospheric interactions studied by European Space Agency and JAXA missions, with attention to cosmic-ray fluxes inferred from cosmogenic isotopes such as ^14C and ^10Be measured at laboratories including Lawrence Livermore National Laboratory and University of Bern. Studies examine correlations with faunal turnovers in the Paleogene and climatic perturbations during events like the Paleocene–Eocene Thermal Maximum, with contributions from researchers at Smithsonian Institution and Natural History Museum, London. While proposals of mass-extinction causation by reversals have been considered in debates involving Royal Society fellows and paleontologists at American Museum of Natural History, consensus emphasizes limited direct biological disruption.

Dating of reversals combines radiometric methods such as argon–argon dating developed at Geological Survey of Japan facilities, uranium–lead techniques refined at Massachusetts Institute of Technology, and astrochronological tuning used by groups at University of Colorado Boulder and GFZ German Research Centre for Geosciences. Paleomagnetic sampling methods standardized by the International Union of Geodesy and Geophysics use oriented cores from the Ocean Drilling Program and continental boreholes logged by the British Geological Survey, with data archived in repositories like the Magnetics Information Consortium and processed using software from Paleomagnetism.org and institutions such as University College London.

Numerical and laboratory dynamo models produced by teams at University of California, Los Angeles, University of Maryland, and the Max Planck Institute for Geophysics inform implications for planetary bodies including Mars and Ganymede, whose remanent crustal magnetism was mapped by missions like Mars Global Surveyor and Galileo. Comparative studies involve researchers at Jet Propulsion Laboratory and the European Southern Observatory, linking paleomagnetic records to thermal evolution models developed with input from the Smithsonian Astrophysical Observatory and the Carnegie Institution for Science. Understanding reversals informs assessments of space weather shielding considered by agencies such as SpaceX and European Space Agency for long-duration human missions.