Plants and the palaeoatmosphere

Compared to the present day, in the Carboniferous the Earth's biomass was much higher, but the primary productivity was of the same order. The biomass stored as 'fossil fuel', estimated at 0.00002% over 65 m.y., is a small proportion of productivity. The Carboniferous vegetation was not a significant carbon sink. Mesozoic atmosphere is discussed in relation to the angiosperms, especially the photosynthetic modifications in C (sub 4) and CAM plants. Taxonomic evidence indicates that the C (sub 3) system is primitive in the angiosperms and the modified systems have a polyphyletic origin. Their development relates more clearly to the water balance rather than to atmospheric CO (sub 2) or O (sub 2) . The angiosperm evolution did not effect the C content of the atmosphere.