Economics, volcanoes, and Phanerozoic revolutions

Abstract

Two intervals of the Phanerozoic stand out as times of biosphere-scale revolution in the sense that biogeochemical cycles came under increased control by organisms. These are the early Paleozoic (extending from just before the Cambrian to the Middle Ordovician, a duration of about 100 m.y.), characterized by the appearance of predators, burrowers, and mineralized skeletons, and by the subsequent diversification of planktonic animals and suspension-feeders; and the later Mesozoic (latest Triassic to mid-Cretaceous, a duration of somewhat more than 100 m.y.), marked by a great diversification of predators and burrowers and by 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 raw materials and energy are supplied at increasing rates, or when organisms gain greater access to these commodities through rising temperatures and higher metabolic rates. Greater per capita availability of resources enables populations to grow; lessens or alters ecological constraints 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 establishment and spread of daughter species arising through founder speciation. Reductions in productivity reinforce adaptational constraints and may bring about extinctions.

Massive submarine volcanism, together with its associated phenomena of warming, sea-level rise, and widening of warm-weather zones, is proposed to be the chief extrinsic trigger for the Phanerozoic revolutions. The later Mesozoic was characterized by continental rifting, which accompanied massive submarine volcanic eruptions that produced large quantities of nutrients and carbon dioxide. This activity began in the Late Triassic and peaked in the mid- to Late Cretaceous. The Early Cambrian was also a time of rifting and may likewise have been marked by large-scale submarine volcanism. Continental and explosive volcanism, weathering, and upwelling are other potential means for increasing evolutionary opportunity, but their effects are either local or linked directly or indirectly with cooling. Intense chemical weathering in the Early Cambrian, however, may have contributed to the early Paleozoic revolution.

The extrinsic stimulus was greatly amplified through positive feedback by the evolution of higher metabolic rates and other means for acquiring, trading, retaining, and recycling resources more rapidly and from a wider range of environments. Because these novelties usually require a high and predictable supply of resources, their evolution is more likely when extrinsically controlled supplies increase rather than when per capita availability is low.

In the view adopted here, the microevolutionary and microeconomic market forces of competition and natural selection operate against a backdrop of macroeconomic supply and demand. Resources are under both extrinsic and intrinsic control. Positive and negative feedbacks link processes at the micro- and macroeconomic levels. This view complements the genealogical and hierarchical conception of evolution by emphasizing that the pattern of descent is influenced by resources and by market forces operating at all scales of space and time.