The era called as 'age of prokaryotic microbes' is:

The term proterozoic comes from the Greek words proteros (meaning first) and zoon (meaning life). Although early fossils are now thought to occur in older, archean rocks, for many years the oldest evidence of life was known from proterozoic strata. The proterozoic represents the last stage of what was once called, precambrian, 3.7-billion-year-long period before the paleozoic era. Many of these life forms developed the ability to photosynthesize. As a byproduct of photosynthesis, they created oxygen and over billions of years this oxygen transformed the Earths atmosphere. Because oxygen was toxic to some early life forms, many went extinct. Others thrived and evolved into the first multicellular organisms, which are preserved as the ediacaran fauna. Both the beginning and end of the proterozoic were marked by widespread glaciation. About one billion years ago the dominant organisms of earth were cyanobacteria and protozoans, therefore, it was named 'proterozoic'. Proterozoic era is called as age of prokaryotic microbes. During archaezoic era, precambrian era and phaenerozoic era microbes are not dominant. So, they are not called as age of prokaryotic microbes. Thus, option D is correct.