Previous studies of photometric time sequences from pulsating aurora have established that the O(1S) metastable leading to the emission of the auroral green line is excited by two processes, one direct, the other indirect, with the indirect precursor having a lifetime of about 0.1s. In this paper we report on new high time-resolution measurements which extend the observations of precursor lifetime down to about 0.01s. Simultaneous observations of pulsations in the Vegard-Kaplan band system were also made in order to obtain direct measurements of the lifetimes of the N2(A 3&Sgr;+u) metastable; these were found to be essentially equal to those of the precursor over the lifetime range from 0.01s to 0.1s, and less well-correlated for longer lifetimes. This result identifies the O(1S) precursors as N2(A 3&Sgr;+u), at least over the altitude range 97 to 125 km.