The strength of the Earth's magnetic field is important to modern society because it protects Earth and its communication satellites from harmful levels of solar radiation. During periods when the Earth's relative magnetic field strength drops (e.g., during solar flares), increased amounts of solar radiation are allowed to penetrate further into the upper atmosphere causing damage to satellites and interfering with shortwave radio communication. For this reason, it is important to understand the natural short-term variability of the Earth's magnetic field. Records of past geomagnetic field behavior are well-preserved by magnetic minerals within volcanic and sedimentary rocks. Although scientists have long used these records to study the long-term history of magnetic polarity reversals, records of more short-lived geomagnetic instabilities are poorly resolved in time, typically incomplete, and lacking in detail. Developing enhanced, global records with precise age control is essential to identifying common trends during and leading to magnetic field instability.
The research supported by this grant aims to produce the most globally complete record of unstable geomagnetic field behavior to date. We plan to integrate magnetic records collected from volcanic and sedimentary rocks from around the world in order to compile a chronologically calibrated, continuous full-vector record of geomagnetic field behavior during the Réunion geomagnetic event, which occurred roughly two million years ago. This research will allow us to address several fundamental questions: How quickly to geomagnetic instabilities manifest themselves? Do geomagnetic instabilities occur synchronously around the world, or do they affect some geographic regions longer and more severely than others? How weak is the Earth's magnetic field during an instability event? In addition to helping resolve these questions, the data generated during this research will be key to future efforts aimed at modeling the complete behavior of the Earth?s magnetic field and will refine the magnetostratigraphy of the Lower Quaternary, thereby improving the correlation of strata on a global scale.
A collaborative team of geoscientists involving students, professors, and post-docs from the University of Wisconsin-Madison, The University of Minnesota, The University of Addis Ababa (Ethiopia), California Ploytechnic State University San Luis Obispo, and Potsdam University (Germany) determined the timing of eruptions of lava flows in Ethiopia and on Reunion Island in the South Indian Ocean. Iron rich mineral int these lava flows record magnetic field directions that are opposite those of the prevailing field at the time and are thus important to understanding the origin and behavior of the deep earth dymano that generates the magnetic field. The eruption ages of two dozen of these lavas have been determined using the 40Ar/39Ar method of radio-isotopic dating. These ages correspond with the time that the magnetic field directions were locked into these rocks as they cooled from a molten to a solid state. The age of lavas at Reunion Island, 2.2 million years ago, is slightly older than the ages of similar lavas at Gamarri, Ethiopia that are 2.1 million years old. Thus there were at least two periods of unusual magnetic field behavior recorded in thie short period of time. A female undergraduate student completed her senior honors thesis as a result ot fhis effort. She will attend graduate school in Geoscience beginning in 2013.
