A simple indicator of research activity throughout the world in any particular specialty within physics is the number of journal references in Physics Abstracts that are classified under that specialty. I have compiled these numbers for most of the classification groups covering geophysics and astrophysics by using each issue of Physics Abstracts from the beginning of 1967 to the end of June 1975. There was a total of 75,245 abstracts. The compilation of the data is described at the end of this paper.
The yearly totals of all geophysics papers processed are given in Table 1. The rise in output is steep through 1971, but thereafter, the overall rate of research output has remained relatively steady at almost 4 times the 1967 rate.