LIVING MATTER AND TERRESTRIAL GLACIATION

Paleogeographic reconstructions and forecasts of climatic change have been based largely on the impact of cosmic and astronomic factors and have tended to ignore the impact of the geochemical activity of living organisms. Yet the CO₂ cycle in the biosphere (volcanic emissions on the income side and photosynthesis and burial of dead organic matter on the outgo side) can have a significant impact on climatic change because of the greenhouse effect. The CO₂ theory is used to explain the sequence of glacial and interglacial stages of the Pleistocene. Active volcanism during the Alpine mountain-building period resulted in a high CO₂ content in the atmosphere fostering the building up of a large phytomass. The continued absorption of CO₂ produced a cooling trend that led to the Ice Age. The spread of the ice sheet reduced the terrestrial biomass and thus the rate of CO₂ absorption, resulting in an increase of CO₂ in the atmosphere and a warming trend. In the interglacial stage that followed, the build-up of biomass again reduced atmospheric CO₂, producing a new cooling trend. This natural glacial-interglacial rhythm has been modified in the last 5,000 years by human activity. Maninduced reduction of phytomass (through deforestation) and, more recently, the intensive combustion of fossil fuels tend to increase the CO₂ content of the atmosphere (in contrast to the natural interglacial process) and make the advent of a new glacial stage unlikely. (The article was contributed by Victor L. Mote, University of Houston.)