Geologic Time Periods
Windows to the Past

Geologic Time Periods

Geologic time periods are what geologists and paleontologists use to organize the time flow of earths history. Because of the huge scope of time, 4.5 billion years, it is helpful to break it up into smaller chunks.


These divisions are not randomly assigned but they roughly correspond to changes in the geology, geography, climate and other characteristics of the earth. For the most part they follow the evolution of life or the lack of it, on earth. Having said that, the changes in living things comes from changes in the state of the earth itself. The transformation may be brought about by some major geologic event like a collision with another traveler through the solar system like a comet or meteor.  Prolonged volcanic episodes can also be the agent of change. 

The system we use today has evolved over time. It is not a static thing. It will change again as scientists learn more about the planet we live on.

How We Name The Divisions of Time 
In the early 1800’s a system for naming geologic time periods was devised using four periods of geologic time. They were named using Latin root words, Primary, Secondary, Tertiary and Quaternary.  We no longer use this system. 


Since that time the system for naming the periods has been constantly changing. As more information is collected, analyzed, and debated, the divisions created for looking at geologic time changes. 


Below is a list of the currently accepted geologic periods. Each period name is a link to a web page with details about the geology, climate, plants and animals of that time.

Keep in mind that this chart is focused on geologic time periods. There are also geologic Eons, Eras, and epochs. For a more comprehensive look at the span of time since the formation of the earth take a look at the geologic time line chart.

Era
Period
Neogene

Quaternary

Paleogene

Tertiary
Cretaceous

Jurassic

Triassic