ECONOMICS, VOLCANOS, AND PHANEROZOIC REVOLUTIONS

Two intervals of the Phanerozoic stand out as times of biosphere-scale revolution in the sense that biogeochemical cycles came under increas ed control by organisms. These are the early Paleozoic (extending from just before the Cambrian to the Middle Ordovician, a duration of abou t 100 m.y.), characterized by the appearance of predators, burrowers, and mineralized skeletons, and by the subsequent diversification of pl anktonic animals and suspension-feeders; and the later Mesozoic (lates t Triassic to mid-Cretaceous, a duration of somewhat more than 100 m.y .), marked by a great diversification of predators and burrowers and b y the rise of mineralized planktonic protists. This paper explores the economic conditions that make such revolutions possible. I argue that opportunities for innovation and diversification are enhanced when ra w materials and energy are supplied at increasing rates, or when organ isms gain greater access to these commodities through rising temperatu res and higher metabolic rates. Greater per capita availability of res ources enables populations to grow; lessens or alters ecological const raints on functional improvement; makes possible the evolution of high metabolic rates (large incomes), which in turn permit improvement in each of several otherwise incompatible functions; and favors the estab lishment and spread of daughter species arising through founder specia tion. Reductions in productivity reinforce adaptational constraints an d may bring about extinctions. Massive submarine volcanism, together w ith-its associated phenomena of warming, sea-level rise, and widening of warm-weather zones, is proposed to be the chief extrinsic trigger f or the Phanerozoic revolutions. The later Mesozoic was characterized b y continental rifting, which accompanied massive submarine volcanic er uptions that produced large quantities of nutrients and carbon dioxide . This activity began in the Late Triassic and peaked in the mid- to L ate Cretaceous. The Early Cambrian was also a time of rifting and may likewise have been marked by large-scale submarine volcanism. Continen tal and explosive volcanism, weathering, and upwelling are other poten tial means for increasing evolutionary opportunity, but their effects are either local or linked directly or indirectly with cooling. Intens e chemical weathering in the Early Cambrian, however, may have contrib uted to the early Paleozoic revolution. The extrinsic stimulus was gre atly amplified through positive feedback by the evolution of higher me tabolic rates and other means for acquiring, trading, retaining, and r ecycling resources more rapidly and from a wider range of environments . Because these novelties usually require a high and predictable suppl y of resources, their evolution is more likely when extrinsically cont rolled supplies increase rather than when per capita availability is l ow. In the view adopted here, the microevolutionary and microeconomic market forces of competition and natural selection operate against a b ackdrop of macroeconomic supply and demand. Resources are under both e xtrinsic and intrinsic control. Positive and negative feedbacks link p rocesses at the micro- and macroeconomic levels. This view complements the genealogical and hierarchical conception of evolution by emphasiz ing that the pattern of descent is influenced by resources and by mark et forces operating at all scales of space and time.