Emergence of complex societies after sea level stabilized



Sea level rose rapidly from the Last Glacial Maximum (LGM, ∼18,000 years ago) until it stabilized about 7000 years ago. A millennium later, the rudiments of early civilizations appeared. However, the factors that might have spurred the first civilizations are a subject of debate, with proposals ranging across many possibilities from drought to the influence of individual rulers.

We hypothesize that sea level stabilization contributed significantly to the rapid advent of civilizations. Evidence from regions around the world shows that societies with class distinctions first emerged near coastal margins [e.g., Day et al., 2004; Kennett and Kennett, 2006], but there is little understanding of this process on a global scale. We show that the stabilization of sea level and the consequent dramatic increase in coastal margin productivity (CMP)—which resulted in increased availability of the high-quality food necessary for the development of urban lifestyles—provide an explanation for the timing and location of emerging civilizations, and their varying regional characters. The coastal margin includes the continental shelf, nearshore upwelling zones, estuaries, and lower river floodplains affected by coastal water levels.