The Tertiary is a geological period that began after the extinction of the dinosaurs 66 million years ago and continued until the first ice age 2.6 million years ago. It is preceded by the Cretaceous and followed by the Quaternary. The period opens with the Cretaceous-Tertiary boundary, one of most easily identifiable strata in geology. This strata is the result of an asteroid impact in what is now the Gulf of Mexico as well as a series of enormous volcanic eruptions that may have been triggered by the impact. The resulting lava flows created what is now the Deccan Traps in southern India.
The name Tertiary was introduced by Italian geologist Giovanni Arduino in 1760. Arduino designated igneous and metaphoric rock as Primary, shales and limestones as Secondary, and sedimentary rock containing fossils as Tertiary. Superficial gravel deposits thought to have been created by glaciers are designated Quaternary. Arduino's Primary layer was later renamed the Paleozoic (old life) in line with Darwinist assumptions. His Secondary layer is now referred to as the Mesozoic (middle life). As a remnant of pre-Darwinist geology, the Tertiary has provoked opposition in recent years from the International Commission on Stratigraphy and others. However, the U.S. Geological Survey continues to recognize the period.
- Division of Geologic Time -- Major Chronostratigraphic and Geochronological Units, USGS, 2010. "Although the Tertiary is not recognized by many international time scales, the GNC agrees that it is important that it be recognized as a system/period; the map symbols “T” (Tertiary) and “Q” (Quaternary) have been used on geologic maps for more than a century and are widely used today."