In this work, we present for the first time undeniable evidence of nano-plastic occurrence due to solar light degradation of marine micro-plastics under controlled and environmentally representative conditions. As observed during our recent expedition (Expedition 7th Continent), plastic pollution will be one of the most challenging ecological threats for the next generation. Up to now, all studies have focused on the environmental and the economic impact of millimeter scale plastics. These plastics can be visualized, collected and studied. We are not aware of any studies reporting the possibilities of nano-plastics in marine water. Here, we developed for the first time a new solar reactor equipped with a nanoparticle detector to investigate the possibility of the formation of nano-plastics from millimeter scale plastics. With this system, correlated with electronic microscopy observations, we identified for the first time the presence of plastics at the nanoscale in water due to UV degradation. Based on our observations, large fractal nano-plastic particles (i.e., >100 nm) are produced by UV light after the initial formation of the smallest nano-plastic particles (i.e., <100 nm). These new results show the potential hazards of plastic waste at the nanoscale, which had not been taken into account previously.