A 30 m.y. stable isotopic record of marine-deposited black carbon from regional ter- restrial biomass burning from the northern South China Sea reveals photosynthetic path- way evolution for terrestrial ecosystems in the late Cenozoic. This record indicates that C3 plants negatively adjusted their isotopic discrimination and C 4 plants appeared grad- ually as a component of land vegetation in East Asia since the early Miocene, a long time before sudden C4 expansion occurred during the late Miocene to the Pliocene. The changes in terrestrial ecosystems with time can be reasonably related to the evolution of East Asian monsoons, which are thought to have been induced by several intricate mechanisms during the late Cenozoic and could contribute significantly to the post-Miocene marine carbonate isotope decline.