Hierarchy classification:

1. top of the aat hierarchies
2. Styles and Periods Facet
3. Styles and Periods (hierarchy name)
4. [styles, periods, and cultures by general era]
5. geologic time scale
6. Precambrian

Anotations

Scope note:

On the geologic time scale, the period preceding the Proterozoic Eon, spanning about 1.5 billion years, in which the Earth's atmosphere was probably of methane, ammonia, and other gases, and the surface cooled enough that rocks and continental plates began to form.