Evolution of the Biosphere

Figure 5b shows the cumulative biomasses for the three life forms. From the Archaean to the future there always exists a prokaryotic biosphere. At 2 Gyr ago eukaryotic life first appears because the global surface temperature reaches the tolerance window for eukaryotes. This moment correlates with the onset of a temperature fall caused by an increasing continental area. The resulting enlargement in the weathering flux takes out CO2 from the atmosphere. In contrast to the eukaryotes the first appearance of complex multicellular life starts with an explosive increase in biomass connected with a strong decrease in Cambrian global surface temperature at about 0.54 Gyr ago. The biological colonization of land surface by metaphyta and the consequent increase in silicate weathering rates caused a reduction in atmospheric CO2 and planetary cooling. Protein sequence analysis has shown that a first appearance of land plants at this time was already possible. Metazoan fecal pellets supplied a new and important transport mechanism of organic carbon to the deep ocean. This provides an additional sink for CO2 in the atmosphere-ocean system.

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