  Using self-consistent models of turbulent particle growth in an evolving
protoplanetary nebula of solar composition we find that recently proposed local
metallicity and Stokes number criteria necessary for the streaming instability
to generate gravitationally bound particle overdensities are generally not
approached anywhere in the disk during the first million years, an epoch in
which meteoritic and observational evidence strongly suggests that the
formation of the first planetesimals and perhaps giant planet core accretion is
already occurring.
