  The discovery of metal-poor stars (where metal is any element more massive
than helium) has enabled astronomers to probe the chemical enrichment history
of the Milky Way. More recently, element abundances in gas inside high-redshift
galaxies has been probed through the absorption lines imprinted on the spectra
of background quasars, but these have typically yielded measurements of only a
few elements. Furthermore, interpretation of these abundances is complicated by
the fact that differential incorporation of metals into dust can produce an
abundance pattern similar to that expected from nucleosynthesis by massive
stars. Here we report the observation of over 25 elements in a galaxy at
z=2.626. With these data, we can examine nucleosynthetic processes independent
of the uncertainty arising from depletion. We find that the galaxy was enriched
mainly by massive stars (M > 15 solar masses) and propose that it is the
progenitor of a massive, elliptical galaxy. The detailed abundance patterns
suggest that boron is produced through processes that act independently of
metallicity, and may require alternative mechanisms for the nucleosynthesis of
germanium.
