Biota and Chemical Weathering

The Earth has an average surface temperature of about 15°C, which is, in terms of planetary conditions suitable for life, the equivalent of winning the cosmic lottery. Yet, without an atmosphere filled with biological waste gases capable of retaining heat (O2, N2O, CH4, CO2), the average temperature of the planet would be about −18°C (Smil 2002), making the present diversity and abundance of life virtually impossible. Thus, since the evolution of prokaryotic heterotrophic organisms early in the Archean some 4 billion years ago, the Earth’s Critical Zone has evolved as a dynamic and generally self-sustaining system. The interplay between biotic and abiotic components of the planet has directed the pace of evolution and shaped the climate of the Earth. This complex system containing life and Earth materials was first termed the biosphere in 1875 by the Austrian geologist Eduard Suess, but it remained for the Russian scientist Vladimir Vernadsky in 1926 to articulate the concept as a scientific paradigm. The processes that control the biosphere are now gaining attention, as one species, Homo sapiens, enters its third century of massive alteration of the planet. A looming issue at this critical juncture in geological and human time is to understand how resilient this system is to human activities.