What is the main reason for the shift in Cenozoic period names?

The main reason for the shift in Cenozoic period names relates to a better understanding of Earth's geological history. As geologists have enhanced their knowledge of the Earth's timeline, particularly through improved dating techniques and fossil records, they have re-evaluated and refined the subdivisions of geological time. This refined understanding has led to clearer distinctions between the various epochs, ages, and periods of the Cenozoic era, emphasizing evolutionary changes in flora and fauna, as well as significant changes in climate and geography that occurred during this time.

While volcanic activity, climate patterns, and tectonic shifts are indeed relevant to the study of geology and play crucial roles in shaping Earth's features and environments, the fundamental driving force behind identifying and naming these periods lies in the comprehensive insights gained from research and understanding of past geological events and life forms. This historical perspective aids in establishing a more accurate framework for studying Earth's geological history and thus leads to these nomenclature shifts.