Long - term patterns in the aging of the scientific literature , 1900 – 20041

Despite a very large number of studies on the aging and obsolescence of scientific literature, no study has yet measured, over a very long time period, the changes in the rates at which scientific literature becomes obsolete. This paper aims at studying the evolution of the aging phenomenon and, in particular, how citation half-lives are changing over more than 100 years of scientific activity. It shows that the average and median age of cited literature has undergone several changes over the period. Specifically, the two World Wars had the effect of raising the average and median age of the cited literature significantly. Moreover, and contrary to a widely-held belief, the age of cited material has risen continuously since the mid-60s. Among the possible explanations for this counter-intuitive phenomenon, the most probable is the levelling off of the growth of scientific literature related to the steady-state dynamics of modern science that follows its exponential growth.