Generation: Paleozoic refers to the era of ancient creatures, from 570 million years ago to 225 million years ago, marking the beginning of a large number of biological development; Mesozoic refers to the middle biological period, from 225 million years ago to 65 million years ago. This period is characterized by the prosperity of reptiles, which mainly lived on land, while the creatures before that mainly lived in water. Cenozoic refers to the modern biological era. From 65 million years ago to the present, its biological species are closely related to modern organisms, and mammals multiply in large numbers.

Ji: Generations are divided into Ji, and each generation can be further divided into several Ji. For example, Paleozoic is divided into Cambrian, Ordovician, Silurian, Devonian and Carboniferous, and Permian has six periods. Mesozoic is divided into Triassic, Jurassic and Cretaceous. Cenozoic is divided into tertiary and quaternary. The names of Ji mostly come from the place names of areas where standard stratigraphic sections were studied earlier or the names of ancient nationalities.