It is tempting to suppose that there is an upper limit to biodiversity, or a global carrying capacity. However, evolutionary innovations, climatic changes, and geological changes crank up this diversity ceiling. Evolutionary innovations occasionally lead to the raising of the global carrying capacity, which would imply a rise in global biodiversity. Climatic and geological processes incessantly increase the complexity of the physical environment - they drive geodiversity to ever-greater levels. The biosphere has always striven to reach this ever-rising biodiversity ceiling, but the major disturbances that have led to mass extinctions have hindered its progress. Thus, the world biota has seldom reached the biodiversity ceiling, which is a theoretical maximum towards which the biosphere strives between perturbations (cf. Kitchell and Carr 1985). For these reasons, the biodiversity is unlikely ever to attain a true steady state; rather, it will increase through time, tracking the increasing diversity of the physical environment, with occasional setbacks caused by mass extinctions (Cracraft 1985). Earth physical complexity might have limits (Valentine 1989) - geodiversity will then limit biodiversity.
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