  We present a novel approach to the study of entanglement decay, which focuses
on collective properties. As an example, we investigate the entanglement decay
of a two-qubit system, produced by local identical reservoirs acting on the
qubits, for three experimentally and theoretically relevant cases. We study the
probability distributions of disentanglement times, a quantity independent of
the measure used to quantify entanglement, and the time-dependent probability
distribution of concurrence. Analytical results are obtained for initially
uniformly distributed pure states. The calculation of these probability
distributions gives a complete insight on how different decoherence channels
affect the entanglement initially contained in the set of two-qubit pure
states. Numerical results are reported for randomly distributed initial mixed
states. Although the paper focuses in Markovian noisy channels, we show that
our results also describe non-autonomous and non-Markovian channels.
