Princeton paleomagnetists put controversy to rest

Princeton - Princeton - Princeton University scientists have shown that, in ancient times, the Earth's magnetic field was structured like the two-pole model of today, suggesting that the methods geoscientists use to reconstruct the geography of early land masses on the globe are accurate. The findings may lead to a better understanding of historical continental movement, which relates to changes in climate. By taking a closer look at the 1.1 billion-year-old volcanic rocks on the north shore of Lake Superior, the researchers have found that Earth's ancient magnetic field was a geocentric axial dipole - essentially a large bar magnet centered in the core and aligned with the Earth's spin axis. Some earlier studies of these rocks had led other teams to conclude that the magnetic field of the ancient Earth had a far more complex structure - some proposing the influence of four or even eight poles - implying that present models of the supercontinents that relied on paleomagnetic data and an axial dipole assumption were wrong. The report, which will appear in the October issue of Nature Geoscience, says that previous efforts to interpret the ancient geomagnetic field in rocks from North America were confused by the rapid migration of the continent toward the equator in the distant past. The researchers "neatly lay to rest the long-standing controversy over the nature of Earth's magnetic field 1.1 billion years ago," writes geoscientist Joseph Meert of the University of Florida in an essay that accompanies the report.