The largest mass extinction in earths history occurred at the end of which era

The largest mass extinction in Earths history occurred at the end "Permian" Era, with the extinction itself being labeled as the "Permian–Triassic extinction event." 

Ifound this on google “the existence of agglomeration economies is central to the explanation of how cities increase in size and population, which places the phenomenon on a larger scale. the concentration of economic activity in cities is one reason for their development and growth.” i hope this you for what your looking for.