1. GEOSPHERE-BIOSPHERE FEEDBACKS AS A TRIGGER FOR THE CAMBRIAN EXPLOSION Werner von Bloh, Christine Bounama, Siegfried Franck Potsdam Institute for Climate Impact Research P.O. Box 601203, 14412 Potsdam, Germany

2. AGU Fall Meeting, December 8-12, 2003 CAMBRIAN EXPLOSION Biological Big Bang 540 million years ago Most modern animal groups appear Why did it happened, when it happened?

3. AGU Fall Meeting, December 8-12, 2003 Model description Franck et al. Tellus 54B, 325, 2002

4. AGU Fall Meeting, December 8-12, 2003 Geosphere-biosphere feedbacks Biological productivity: temperature tolerance windows i=1procaryotes[2°C,100°C] i=2eucaryotes[5°C,45°C] i=3complex multicellular life[0°C,30°C]

5. AGU Fall Meeting, December 8-12, 2003 Geosphere-biosphere feedbacks Biological enhancement of weathering: (Lenton and von Bloh, GRL 28 (9),1715, 2001)

6. AGU Fall Meeting, December 8-12, 2003 Model results Evolution of global surface temperature. Evolution of the cumulative biosphere pools for procaryotes, eucaryotes, and complex multicellular life.

7. AGU Fall Meeting, December 8-12, 2003 Model results

8. AGU Fall Meeting, December 8-12, 2003 Stability diagram

9. AGU Fall Meeting, December 8-12, 2003 Conclusions The Cambrian explosion could have been triggered by nonlinear geosphere-biosphere interactions (von Bloh et al., GRL 30 (18), 1963, 2003). External perturbations (e.g. „snowball Earth“ events, continental breakup) have the potential to initiate an earlier appearance of complex multicellular life. The model exhibits bistability for a certain range of the biotic enhancement factor.