  Firestone (2014) asserted evidence for numerous (23) nearby (d<300 pc)
supernovae within the Middle and Late Pleistocene. If true, this would have
strong implications for the irradiation of the Earth; at this rate, mass
extinction level events due to supernovae would be more frequent than 100 Myr.
However, there are numerous errors in the application of past research. The
paper overestimates likely nitrate and 14C production from moderately nearby
supernovae by about four orders of magnitude. Moreover, the results are based
on wrongly selected (obsolete) nitrate and 14C datasets. The use of correct and
up-to-date datasets does not confirm the claimed results. The claims in the
paper are invalidated.
