  Future generation of gravitational wave detectors will have the sensitivity
to detect gravitational wave events at redshifts far beyond any detectable
electromagnetic sources. We show that if the observed event rate is greater
than one event per year at redshifts z > 40, then the probability distribution
of primordial density fluctuations must be significantly non-Gaussian or the
events originate from primordial black holes. The nature of the excess events
can be determined from the redshift distribution of the merger rate.
