tokens: function at the low end. If the space density of metal-poor GCs is ∼2 Mpc −3 , as estimated by Boylan-Kolchin ( 2017 ) using the correlation between GCs and dark matter halos, then the associated stellar density is about half the above value, considering also the metal-rich GCs that formed later. Evidently, a high fraction of star-forming regions included at least one GC before about half the age of the universe. A similar calculation illustrates the importance of GC formation to the universal SFR at early times. If we consider that the duration of the star formation event that made a GC was Δ t , and the redshift range over which they formed was from z = 7 to 2, a period of 2.6 Gyr, then the average SFR from GC-forming events with M max ∼ 10 6 M ⊙ is (5 × 10 7 M ⊙ /Δ t ) × (Δ t /2.6 Gyr) × (8 Mpc −3 ), where the second term is the fraction of time each event occupies in the GC-forming era. The resultant average associated SFR is 0.15 M ⊙ yr −1 Mpc −3 , which is the same as the peak value of the comoving cosmic SFR density in the universe that occurs at redshift ∼2 (Madau Dickinson 2014 ). These two calculations suggest that the early universe was filled with star-forming regions containing young massive clusters (YMCs) that ended up as today’s GCs. There was little additional star formation making smaller clusters or OB associations that dispersed, aside from the smaller clusters and associations directly connected with the GCs. Today the mass density of GC stars is their space density times their average mass of ∼2 × 10 5 M ⊙ (Harris 2001 ), or 1.6 × 10 6 M ⊙ Mpc −3 . This is 0.26% of the current total stellar mass density from Madau Dickinson ( 2014 ), a factor of ∼1/380. The first factor of 50 in this 380 is presumably from scattered stars that formed with the GCs, and then the remaining factor of ∼8 would be from stars that formed recently without making massive clusters. We can also learn about early star formation in dwarf galaxies from their old stellar populations. WLM has an old metal-poor GC whose luminosity suggests that it contains ∼10 6 M ⊙ of stars (Elmegreen et al. 2012 ). The mass of other stars at the same age and metallicity is comparable to this (Leaman et al. 2012 ; Larsen et al. 2014 ), suggesting that the GC was a high fraction of the total WLM mass when it formed (Elmegreen et al. 2012 ). Similarly, the GC mass in the Fornax dwarf spheroidal was ∼0.25 of the galaxy stellar mass when the GC formed (Larsen et al. 2012 ). For IKN and NGC 147, these fractions are ∼0.5 and 0.06, respectively (Larsen et al. 2014 , 2018 ). These are enormously high fractions, especially considering the additional cluster mass that might have been present in the full cluster mass function. Perhaps the clustered fraction of stars at birth was larger than the 25% assumed above, even close to 100% as suggested by Messa et al. ( 2018 ) for regions with high SFR densities. In either case, the star formation events that formed the observed
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