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EarthWord – Tertiary

March 21, 2016

The Tertiary is a system of rocks, above the Cretaceous and below the Quaternary, that defines the Tertiary Period of geologic time. T

EarthWords is an on-going series in which we shed some light on the complicated, often difficult-to-pronounce language of science. Think of us as your terminology tour-guides, and meet us back here every week for a new word!

Skeleton of Ambulocetus natans, an ancestor of modern whales that lived during the Eocene Epoch, a part of the Tertiary Period. By Momotarou2012 – Own work, via Wikimedia Commons


  • The Tertiary is a system of rocks, above the Cretaceous and below the Quaternary, that defines the Tertiary Period of geologic time. The Tertiary Period began about 66 million years ago with a mass extinction that ‘clocked’ the dinosaurs and ended when the ice ages of the Quaternary Period began, about 2.6 million years ago. These dates have been adjusted as science advances or when new evidence is found.


  • Tertiary comes from the Latin word “tertiarius,” which actually means “the third.” Tertiary was first used to describe the third of only four age classifications for rocks.

Use/Significance in the Earth Science Community:

  • The Tertiary Period began abruptly when a meteorite slammed into the earth, leading to a mass extinction that wiped out about 75 percent of all species on Earth, ending the reptile-dominant Cretaceous Period and Mesozoic Era. This event formed the Cretaceous-Tertiary, or K-T, boundary. While the Tertiary began with a biosphere in ruins, it recovered. Mammals became dominant and humanity evolved to the genus of modern humans. The Tertiary began hot and humid and ended in an ice age.
  • The current International Geological Timescale uses the terms Paleogene and Neogene instead of Tertiary. It recognizes three periods of geologic time, including the Quaternary, in the Cenozoic Era.


Next EarthWord: What do you call it when the earth rocking and rolling beneath your feet is due to human activities?

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