The coccoliths are major contributors to the particulate inorganic carbon in the ocean. They are extremely difficult to weigh because they are too small to be manipulated. We propose a universal method to measure thickness and weight of fine calcite using polarizing microscopy that does not require fine-tuning of the light or a calibration process. This method named "bidirectional circular polarization" uses two images taken with two directions of a circular polarizer.

Calcareous nannoplankton are photosynthetic plankton producing micrometric calcite platelets having a fossil record covering the past 200 Myr. Based on species richness, platelets size and abundance we observed four evolution phases through time: Jurassic–Early Cretaceous invasion phase of the open ocean, Early Cretaceous–K–Pg extinction specialization phase to the ecological niches, post-K–Pg mass extinction recovery and Eocene–Neogene establishment phase with domination of a few small species.