Periods of the Cenozoic Era

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Periods of the Cenozoic Era

An artist rendering of prehistoric times
Smilodon and mammoth evolved during the Cenozoic Era. Getty/Dorling Kindersley

Our current Era in the Geologic Time Scale is called the Cenozoic Era.  Compared to all of the other Eras throughout the history of the Earth, the Cenozoic Era has been relatively short so far. Scientists believe large meteor strikes hit the Earth and created the great K-T Mass Extinction that completely wiped out the dinosaurs and all of the other larger animals.  Life on Earth once again found itself trying to rebuild back to a stable and thriving biosphere.

 It was during the Cenozoic Era that the continents, as we know them today, had fully split and drifted into their current positions.  The last of the continents to reach its place was Australia.  Since the land masses were now spread farther apart, climates were now very different meaning new and unique species could evolve to fill the new niches the climates had available.

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The Tertiary Period (65 million years ago to 2.6 million years ago)

Pasaichthys fossil from the Tertiary Period

The first period in the Cenozoic Era is called the Tertiary Period.  It began directly after the K-T Mass Extinction (the “T” in “K-T” stands for “Tertiary”).  At the very beginning of the time period, the climate was much hotter and more humid than our current climate.  In fact, tropical regions were most likely too hot to support the various forms of life we would find there today. As the Tertiary Period wore on, the Earth’s climate overall became much cooler and drier.  

Flowering plants dominated the land, except for in the coldest climates. Much of the Earth was covered in grasslands.  The animals on land evolved into many species over a short period of time.  Mammals, especially, radiated in different directions very quickly.  Even though the continents were separated, there were thought to be several “land bridges” that connected them so land animals could migrate easily between the different land masses.  This allowed new species to evolve in each climate and fill the available niches.

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The Quaternary Period (2.6 million years ago to the present)

The present day earth

James Cawley / Getty Images

We are currently living the Quaternary Period.  There was no mass extinction event that ended the Tertiary Period and started the Quaternary Period.  Instead, the division between the two periods is somewhat ambiguous and often argued by scientists.  Geologists tend to set the boundary at a time that had to do with the cycling of glaciers. Evolutionary biologists sometimes set the division around the time when the first recognizable human ancestors were thought to have evolved from primates.  Either way, we do know that the Quaternary Period is still going on right now and will continue until another major geological or evolutionary event forces the change to a new period of the Geologic Time Scale.

The climate rapidly changed at the very beginning of the Quaternary Period.  It was a time of rapid cooling in the Earth’s history.  Several ice ages happened during the first half of this period which caused glaciers to spread in the higher and lower latitudes.  This forced most of the life on Earth to concentrate its numbers around the equator.  The last of these glaciers receded off of the northern latitudes within the last 15,000 years. This means any life in these areas, including much of Canada and the Northern United States, has only been in the area for a few thousand years as the land began to once again be colonized as the climate changed to be more temperate.

The primate lineage also diverged in the early Quaternary Period to form the hominids or early human ancestors.  Eventually, this lineage split into the one that formed Homo sapiens, or the modern human being. Many species have gone extinct, thanks to humans hunting them and destroying habitats.  Many large birds and mammals went extinct very soon after humans came into existence.  Many people think we are in a period of mass extinction right now due to human interference.

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Scoville, Heather. "Periods of the Cenozoic Era." ThoughtCo, Sep. 15, 2021, Scoville, Heather. (2021, September 15). Periods of the Cenozoic Era. Retrieved from Scoville, Heather. "Periods of the Cenozoic Era." ThoughtCo. (accessed June 9, 2023).