Britannica Sources used in this answer

How do the Paleogene and Neogene periods relate to the former Tertiary Period?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Messinian Stage — Tertiary Period Gypsum cones, which resulted from the evaporation of the Mediterranean Sea during the Messinian Salinity Crisis, in the Sorbas basin, Spain.

The former Tertiary Period is no longer an official unit of geologic time. In 2008, the International Commission on Stratigraphy (ICS) officially replaced the Tertiary with two distinct periods: the Paleogene Period and the Neogene Period.123

Together, these two periods span the same interval previously occupied by the Tertiary, covering the time from approximately 66 million to 2.6 million years ago. The relationship is structured as follows:13

Paleogene Period (66 to 23 million years ago): Comprises the Paleocene, Eocene, and Oligocene epochs.13
Neogene Period (23 to 2.6 million years ago): Comprises the Miocene and Pliocene epochs.13

The transition from the Paleogene to the Neogene occurs at the 23-million-year mark, which corresponds to the boundary between the Oligocene and Miocene epochs. While the term Tertiary is now considered obsolete by many authorities, it remains historically significant as the framework established by Giovanni Arduino in 1760, which provided the foundation for modern stratigraphy.32