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Geologic eras

The following is from Exploring the Environment, through their Global Climate Change Education problem-based learning (PBL) website. The Center for Educational Technologies at Wheeling Jesuit University.



Earth is four thousand, six hundred million years old (4,600 million = 4.6 billion), give or take a few hundred million years.

How old is that, really? It is older than anything you can see around you, like trees, buildings, or roads. It is even older than the hills, valleys, and rivers around where you live. It is so old that the world’s mountains have been built up and worn down many times, the continents have wandered across the face of Earth, and plants and animals have changed many times, from amoebas to dinosaurs to people.

The age is so long compared to all periods of time that we are familiar with, that it has a special name: Geologic time.

The age of Earth is as vast in time as the universe is vast in space. One way to try to get a “feel” for how big it is, is to break the number down into smaller pieces that perhaps we can understand. Just for fun you might try the activity, “What is a Million?” 

One comparison is to compare the length of Earth’s history, to the length of a football field in the geologic time activity.

Here we use another comparison to help show the span of time since the formation of Earth: “The Stairway of Time.”

The Stairway of Time Geologic eras

Button that takes you to the Cenozoic Era page. Button that takes you to the Mesozoic Era page. Button that takes you to the Paleozoic Era page. Button that takes you to the Precambrian Eon page.

The bottom of the Stairway represents the formation of Earth 4.6 billion years ago.
The top represents the present or today.
The different steps represent different segments of time in Earth’s history.
Something different was happening during each segment.

Many exciting changes have happened on Earth since it formed.

To find out a little about the changes that occurred during the different time segments, click on the names on the Staircase or on the list below:

  1. Cenozoic Era
  2. Mesozoic Era
  3. Paleozoic Era
  4. Precambrian Eon

Are you curious about where the strange names on the Staircase of Time come from? Do you want to know“How old is that rock?” and how geologic time periods were determined?


from http://msascienceonline.weebly.com/geologic-time-scale.html
Geologic time scale cartoon


How long is one period of time, compared to another? How long have we humans been around, compared to the age of the Earth?
If you think of Earth’s entire history as having happened in 24 hours, modern humans have been here for only about 3 seconds before midnight.


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