Answer:
A. Mass extinctions, Wegenerian cycles, and the emergence of new life forms
Step-by-step explanation:
Every geological period is characterised by episodes of mass extinction, Wegenerian cycles and emergence of new life forms.
The boundaries of most geologic periods are usually mass extinction periods and these mass extinction activates new evolution of life forms. For example, the period between the Mesozoic era and Cenozoic is marked by the K-T extinction where dinosaurs and about 75% of all life became extinct. New advanced mammals sprang up shortly after the extinction in the Cenozoic era.
During the geologic period, series of tectonic activities are in play as a result of the internal workings of the earth. Continents splits apart and new landform arises at plate boundaries. This is the Wegenerian cycle. The external processes like weathering and erosion helps to recycle the landforms and keeps it in check.