  Often in nature the temporal distribution of inhomogeneous stochastic point
processes can be modeled as a realization of renewal Poisson processes with a
variable rate. Here we investigate one of the classical examples, namely the
temporal distribution of polarity reversals of the geomagnetic field. In spite
of the commonly used underlying hypothesis, we show that this process strongly
departs from a Poisson statistics, the origin of this failure stemming from the
presence of temporal clustering. We find that a Levy statistics is able to
reproduce paleomagnetic data, thus suggesting the presence of long-range
correlations in the underlying dynamo process.
