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Make Your Own Timeline of Life April 23 2021, 0 Comments

The Timeline of Life, with its starring role in the Coming of Life Great Lesson, is an important material for elementary Montessori classrooms. Teachers must either purchase one or make their own. The commercially available ones all have issues, which make some of them undesirable for the classroom. See my previous blog article, What goes on a Timeline of Life? for the details. That’s the bad news.

The good news is that making a Timeline of Life isn’t as difficult as it first appears. It is a timeline of the Phanerozoic Eon. Here are the measurements for a timeline that is three meters long. On it, 1 cm symbolizes 2 million years. The Phanerozoic Eon itself takes up about 2.71 meters. The extra length allows you to add the late Proterozoic Ediacaran biota and gives you a border at the ends of the chart.  

Geologic time interval

Start and end times (Ma= million years ago)

Duration in millions of years

Length on the timeline in centimeters

Paleozoic Era

 541-252 Ma  

289

144.5

Cambrian Period

 541-485 Ma   

  56

28

Ordovician Period

 485-444 Ma

  41

   20.5

Silurian Period

 444-419 Ma

  25

   12.5

Devonian Period

 419-359 Ma

  60

30

Carboniferous Period

 359-299 Ma

  60

30

Permian Period

 299-252 Ma

  47

   23.5

Mesozoic Era

 252-66 Ma

186

93

Triassic Period

 252-201 Ma

  51

   25.5

Jurassic Period

 201-145 Ma

 56

28

Cretaceous Period

 145-66 Ma

 79

   39.5

Cenozoic Era

 66 Ma-present

 66

33

Paleogene Period

 66-23 Ma

 43

   21.5

Neogene Period

 23-2.6 Ma

   20.4

   10.2

Quaternary Period

2.6 Ma-present

     2.6

     1.3

 

Timelines are much more than just a time scale. This one needs illustrations of life and how it has changed over time. I was happy to find that the United States Geological Survey (USGS) has a great source of these illustrations online. In 2020, a physical exhibit called “Trek Through Time” opened at the USGS headquarters in Reston, Virginia. That exhibit is also available online at https://www.usgs.gov/science-support/osqi/youth-education-science/trek-through-time. It is illustrated with posters for each time period. Here is an example, the poster for the Ordovician Period.  

Click on the “Let’s Take a Walk” link to access the posters for the time periods. These high quality illustrations are in the US public domain, and you can print them for your classroom. Click on the thumbnail illustrations of each poster to get the files for printing. Select “original” to get the largest size, which can be printed on letter-sized paper. These posters have a small world map inset that shows the land masses at that time. A red dot marks the location that will become Reston, Virginia. The description of each time period has information about the biota of the Earth, how our planet looked, and what its climate was like. It also gives conditions in Virginia at that time. This information would make good text cards to go with the posters.

For the Ordovician and Silurian Periods, the poster is wider than the time period. For the Cenozoic, the six posters will have to be stacked one on top the other because each of them is about as wide as the whole era.

The Trek Through Time posters are a good start to a useable, up-to-date timeline of life. You can add organisms as the children explore prehistoric life. When children see a dynamic timeline develop as they add their own contributions, it can be more engaging than working with one that is all done for them. Adding new fossil discoveries can be especially inspiring. 

If you have good illustrations of animals from an otherwise not-so-great timeline, you may be able to use them on your new timeline, but carefully read and verify any information on cards for the organisms and make sure that you place them in the correct time period. Wikipedia can be a great help in finding when an animal lived if you have a name it.

Illustrations of plants from older timelines are usually not worth keeping. There are good black-and-white drawings of ancient plants at the Virtual Paleobotany website, https://ucmp.berkeley.edu/IB181/VPL/Dir.html. You can also find illustrations in books on fossil plants and plant evolution, which you may be able to get from a library.

What about all those red lines that appeared on the original Montessori timelines? I recommend that you leave them off unless you can connect organisms in valid lineages. If you can’t stand back and see meaning and pattern in the lines, they are likely to distract rather than give a useful impression. Certainly, you should not have any lines that come together. The Tree of Life branches out.

Add the five mass extinctions by drawing a thicker black line after the Ordovician, Devonian, Permian, Triassic, and Cretaceous Periods. These events have been major factors in the shaping of life on Earth. 

If you and your children are interested in learning more about mammals after the dinosaur extinction, my new material, The Story of Mammals: From the dawn of life to the present day, has instructions for making a Cenozoic timeline that is long enough to show the many changes in mammals in the last 66 million years. This set includes the file to print 84 picture cards to place on the timeline and a 76-page booklet of lessons. You can see it at https://big-picture-science.myshopify.com/products/the-story-of-mammals.    

I hope that you and your children enjoy your explorations of life through time.