The History of the Earth’s Magnetic Field Strength Over the Last Four Million Years: An Updated Global View
Dr. Lisa Tauxe
University of California, San Diego
In 1600, William Gilbert published the first book examining the Earth’s magnetic field from a global perspective. He famously said, “The Earth itself is a great magnet”. While this is mostly true there are significant departures from this simple bar magnet assumption. For example, the Earth’s magnetic field “flips” occasionally and other effects complicate our ability to track the motions of continents accurately. If the magnetic field were like that of a simple bar magnet centered in the Earth and aligned with the spin axis (a geocentric axial dipole), the field strength would be twice as strong at the poles than at the equator. The present magnetic field has an North-South hemispheric asymmetry in field strength that appears to persist over at least 100,000 years. Some modelling suggests that this asymmetry is only expected when the magnet bar magnet is strong (like today’s) and should disappear when the field is weaker (like it was, say, five million years ago). To test this hypothesis, we require estimates of the ancient field strength from around the world from geologic records. This lecture will focus on how sediments and lava flows retain a record of the Earth’s magnetic field and what the results are from a global campaign to obtain data to address this problem.
Dr. Lisa Tauxe graduated with a Bachelor’s degree from Yale University in 1978, and with a Ph.D. degree from Columbia University in 1983. She is a Fellow of the American Geophysical Union, the Geological Society of America, the American Association for the Advancement of Science and the European Geosciences Union. She won the George P. Woolard Award and the Arthur L. Day Medal from the Geological Society of America, the Franklin Medal from the Franklin Institute, the Petrus Perigrinus Medal from the European Geosciences Society, the Humboldt Prize from the Deutsche Forschungs Gemeinde, was elected to the National Academy of Sciences, the American Academy of Arts and Sciences and the Chinese Academy of Sciences, as well as winning the John Adam Fleming Medal from the American Geophysical Union. Tauxe has authored or co-authored over 250 articles in peer-reviewed journals as well as two books on the subject of Rock and Paleomagnetism. She founded and helps to maintain the widely used software for the rock and paleomagnetic community. She served as president of the Geomagnetism/Paleomagnetism Section and as the General Secretary/Treasurer of the American Geophysical Union. She is currently a Distinguished Professor, Emerita at the Scripps Institution of Oceanography, UC San Diego.