Diatoms Are Important Photosynthetic Organisms in Marine Environments

Diatoms are important photosynthetic organisms in marine environments. This group evolved relatively recently (during the Mesozoic Era) . Diatoms also play an important role in the transfer of silica to ocean sediments. What is the importance of the recent evolution of these organisms to the marine environment in which they live?

A) Because they are photosynthetic, they increase the concentration of oxygen in the atmosphere.
B) Because they have silica exoskeletons, they do not deplete calcium needed by foraminiferans.
C) More recently evolved groups of protists continue to alter marine environments, much like earlier groups of protists.
D) More recently evolved groups of protists continue to alter marine environments, in response to the evolution of the ability to ingest other protists.