Tertiary Period: History and Evolution of a Geologic Era
The Tertiary is a term once used to describe a vast stretch of geologic time spanning from approximately 66 million to 2.6 million years ago. Marking the dawn of the Cenozoic Era, this period began with the dramatic Cretaceous–Paleogene (K-Pg) extinction event—the event that saw the disappearance of non-avian dinosaurs—and concluded with the onset of the Quaternary glaciation.
While the term remains common in some scientific literature and general conversation, it is now considered obsolete by formal stratigraphic standards. The International Commission on Stratigraphy (ICS) replaced the Tertiary in the late 1980s, splitting its duration into two distinct periods: the Paleogene and the Neogene.
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Key Facts
- Time Span: Approximately 66 million to 2.6 million years ago.
- Start Event: The K-Pg extinction event (extinction of non-avian dinosaurs).
- End Event: The beginning of the Quaternary glaciation.
- Current Status: Obsolete; replaced by the Paleogene and Neogene periods.
- Era: Part of the Cenozoic Era.
The Historical Evolution of the Term
The concept of the Tertiary was first introduced in the mid-18th century by Giovanni Arduino. Based on his observations of the geology in Northern Italy, Arduino classified geologic time into three primary stages: primitive (primary), secondary, and tertiary. A fourth stage, the Quaternary, was added later.
In the early days of geology, some scriptural geologists attempted to align these periods with the Biblical narrative, suggesting that the rocks of the Tertiary were associated with the Great Flood.
The Influence of Charles Lyell
In 1833, the influential geologist Charles Lyell integrated the Tertiary Period into a more detailed classification system. His work was based on fossil mollusks collected from Sicily and Italy between 1828 and 1829. Lyell subdivided the period into four epochs based on how closely the fossil mollusks resembled modern species, assigning them Greek names: Eocene, Miocene, Older Pliocene, and Newer Pliocene.
However, as geologists applied this system to North America and other parts of Europe, they found that using mollusks as the primary marker was inapplicable. Consequently, the definition was revised, and the epochs were renamed and redefined.
Transition to Modern Stratigraphy
For decades, the Tertiary was formally defined as the span between 65 and 1.8 million years ago. Over time, scientific refinements shifted these boundaries to approximately 66 million and 2.6 million years ago, respectively.
In 1989, the International Commission on Stratigraphy (ICS) officially removed "Tertiary" from its stratigraphic charts. In its place, they adopted the terms Paleogene and Neogene—terms originally coined in the 1850s by Austrian geologist Moritz Hörnes. Although the ICS briefly considered including the Quaternary within the Neogene in 2004, the Quaternary was restored to full period status by 2009.
Despite this formal removal, the term "Tertiary" proved resilient. In 2006, researchers noted that the term was still more frequently used in scientific discourse than its formal replacements, the Paleogene and Neogene.
Modern Equivalents and Subdivisions
Today, the time span formerly known as the Tertiary is understood as the interval between the Mesozoic Era and the Quaternary Period. It is subdivided into five distinct epochs, each representing a specific window of Earth's history.
| Epoch | Time Span (Millions of Years BP) |
|---|---|
| Paleocene | 66 – 56 |
| Eocene | 56 – 33.9 |
| Oligocene | 33.9 – 23.04 |
| Miocene | 23.04 – 5.333 |
| Pliocene | 5.333 – 2.58 |
This sequence extends precisely to the Gelasian Stage, which marks the first stage of the Pleistocene.
Frequently Asked Questions
Why is the term "Tertiary" considered obsolete?
The International Commission on Stratigraphy (ICS) eliminated the term in the late 1980s to provide a more precise division of time, splitting the span into the Paleogene and Neogene periods.
What event marked the beginning of the Tertiary?
The period began with the Cretaceous–Paleogene (K-Pg) extinction event, which is most famous for the extinction of non-avian dinosaurs.
Who first proposed the division of the Tertiary into epochs?
Charles Lyell subdivided the period in 1833, originally using fossil mollusks from Italy and Sicily to define the Eocene, Miocene, and Pliocene epochs.
What is the difference between the Paleogene and the Neogene?
The Paleogene is the earlier portion of the former Tertiary (comprising the Paleocene, Eocene, and Oligocene), while the Neogene is the more recent portion (comprising the Miocene and Pliocene).
When did the Tertiary period end?
The period ended approximately 2.6 million years ago with the beginning of the Quaternary glaciation.