Geosphere-Biosphere Feedbacks as a Trigger for the Cambrian explosion

Details Geosphere-Biosphere Feedbacks as a Trigger for the Cambrian explosion Geosphere-Biosphere Feedbacks as a Trigger for the Cambrian explosion

Dec 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufm.u52c..06v&link_type=abstract

American Geophysical Union, Fall Meeting 2003, abstract #U52C-06

Physics

0315 Biosphere/Atmosphere Interactions, 0330 Geochemical Cycles, 3220 Nonlinear Dynamics, 8125 Evolution Of The Earth

Scientific paper

A new hypothesis for the cause of the Cambrian explosion is presented. The Cambrian explosion 542 Myr ago is characterized by a sudden increase of biomass and a rapid cooling, which amplified the spread of complex multicellular life. The evolution of the planet Earth is described by the co-evolution of the geosphere-biosphere system. A conceptual model for the global carbon cycle of the Earth containing the reservoirs mantle, ocean floor, continental crust, continental biosphere, the kerogen, as well as the aggregated reservoir ocean and atmosphere is presented. In this study the evolution of the mean global surface temperature, the biomass, and reservoir sizes over the whole history and future of the Earth under a maturing Sun is investigated. Here we specify our previously published Earth system model (Franck et al., 2002) by introducing three different types of biosphere: procaryotes, eucaryotes, and complex multicellular life. They are characterized by different temperature tolerance windows and biotic amplification factors of silicate weathering. The biotic enhancement of weathering by complex multicellular life adds an additional feedback to the system and triggers the Cambrian explosion. The Cambrian explosion was mainly driven by extrinsic environmental causes, i.e. a gradual cooling of the Earth. The Cambrian explosion was so rapid because of a positive feedback between the spread of biosphere, increased silicate weathering, and a consequent cooling of the climate. The environment itself has been actively changed by the biosphere maintaining the temperature conditions for its existence. Furthermore, it can be shown that the coupled geosphere-biosphere system exhibit s bistability: there exist two stable model solutions for a certain interval of the biotic enhancement factor, one solution with and one without complex multicellular life. In particular, cooling events in the Neoproterozoic, could force a premature appearance of complex multicellular life. Frank, S., Kossacki, K.J., von Bloh, W., and Bounama, C., 2002. Long-term evolution of the global carbon cycle: historic minimum of global surface temperature at present. Tellus 54B, 325-343.

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