IMPLICATIONS OF THE LATE PALEOZOIC OXYGEN PULSE FOR PHYSIOLOGY AND EVOLUTION

The late Palaeozoic was marked by significant changes in atmospheric c hemistry and biotic composition. Geochemical models suggest a marked i ncrease and then decline of atmospheric oxygen and associated shifts i n the concentration of carbon dioxide. Although the actual magnitude o f these changes is uncertain, the pulse of oxygen concentration may ha ve reached a maximum of 35% and then dropped to 15% (compared with the present 21%). This oxygen pulse may have influenced the evolution of major groups of organisms.