After the Cambrian explosion, there was a continuous decrease of biomass in all pools. At 0.35 Gyr ago there was a slight drop in the global temperature connected with the rise of vascular plants. At this time weathering rates were increased due the elevated partial pressure of CO2 in the soil by root respiration. The continuous decrease in biomass of primitive life forms (prokaryotes and eukaryotes) since the Cambrian explosion is related to the fact that Phanerozoic surface temperatures are below the optimum for these life forms. The decrease in biomass of complex life forms is due to the fact that there is a continuous decrease in Phanerozoic atmospheric carbon content. At present the biomass is almost equally distributed between the three pools and the mean global surface temperature of about 15 ° C is near the optimum value for complex multicellular life.
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