Multifractality and punctuated equilibrium in the Earth's magnetic field polarity reversals.

The Earth's magnetic field has reversed its polarity hundreds of times in the Earth's history. This phenomenon is generally viewed as due to a Poisson nonstationary process. Here, the geomagnetic chron time length sequence, for the past 166 Ma, is analyzed using a multifractal approach, based on "singularity analysis". The existence of a multifractal structure is the signature of the occurrence of "punctuated equilibrium", which can be read as an indication of a critical configuration of the geodynamo. The results obtained are compared with those from a prototypical model of a dynamical system, introduced by Seki & Ito [1993], and are discussed in the context of fluid motions within the Earth's outer liquid core.