ABSTRACT
This chapter outlines the data which have been obtained and the conclusions which have been drawn from them, explores the extent to which stable carbon isotope studies have contributed to the understanding, and finally considers some possibilities for further contributions from work on stable carbon isotopes to this field. Data from palaeontology, from other earth sciences, and from molecular genetics and cladistics, has enabled a tentative timetable to be established for the evolution of pho-tosynthetic organisms and for changes in the atmospheric environments. Measurements of the natural abundance of the stable isotopes of carbon have contributed to our understanding of this area. The structure of ribulose-1,5-bisphosphate carboxylase-oxygenase, the core carboxylase through which 95% or more of the total organic in harvestable plant material has been routed, shows phylogenetic variations in nucleotide sequence within the gene family.
