Editor's Summary
2 November 2006
A snowball's chance
The presence of Proterozoic glacial deposits at near-equatorial palaeomagnetic latitudes can be explained by 'snowball Earth' episodes of global refrigeration. Alternatively, extreme orbital obliquity may have reversed the relationship between the poles and the Equator, allowing ice ages in the tropics. Or perhaps we are viewing the past using unfounded assumptions about the behaviour of Earth's magnetic field based on what we see today. Yale geophysicist David Evans has devised a test to distinguish between these possibilities. The study uses the palaeomagnetism of ancient evaporite basins to test for consistency between geomagnetic and palaeoclimatic reference frames. The highobliquity hypothesis fails the test, since Precambrian evaporites are not equatorial as predicted by high-obliquity global climate models. The consistency of the evaporite basin palaeomagnetic latitudes over the past 2 billion years argues for the stability of the familiar dipole geocentric magnetic field over this time interval.
News and Views: Geophysics: Same old magnetism
Latitudes at which ancient salt deposits occur show that Earth's magnetic field has always aligned along its rotation axis. One possible implication is that ancient global glaciations were not caused by a realignment of this axis.
Edward Irving
doi:10.1038/444043a
Article: Proterozoic low orbital obliquity and axial-dipolar geomagnetic field from evaporite palaeolatitudes
David A. D. Evans
doi:10.1038/nature05203
Abstract | Full Text | PDF (1,046K) | Supplementary information
