Final answer:
Eons on the geologic time scale are divided into eras, which are large divisions representing significant changes in Earth's geology, climate, and the evolution of life.
Step-by-step explanation:
Eons on the geologic time scale are divided into eras. The eons, such as the Hadean, Archean, Proterozoic, and Phanerozoic, represent the largest time spans in Earth's history. Each eon is further subdivided into smaller units of time. Within an eon, the next level of division is eras, followed by periods, epochs, and eventually ages. Eras include significant spans of time like the Mesoproterozoic, Neoproterozoic, Paleozoic, Mesozoic, and Cenozoic, each marked by major changes in Earth's geology, climate, and the evolution of life.
For instance, the Phanerozoic eon is divided into three eras: the Paleozoic, Mesozoic, and Cenozoic. These eras are known for their distinct biological, tectonic, and climatic events, with the Paleozoic era marked by the emergence of life, the Mesozoic by the reign of the dinosaurs, and the Cenozoic, which is the current era, by the rise of mammals. The significance of each era reflects major evolutionary and geological shifts that have occurred throughout Earth's long history.