In this paper we study the rooted tree model applying the concepts of
probability to obtain results of importance in understanding power-law
distributions in pure populations and also in an ensemble of pure pop
ulations. The well-known Gutenberg-Richter relation, which is an empir
ical relation providing the number of earthquakes whose magnitude exce
eds a given value, is shown to be an asymptotic form of survivor funct
ion of earthquake magnitudes. The implications of this model are brief
ly discussed in relation to other branches of sciences where power-law
distributions are encountered.