Make Your Own Timeline of Life April 23 2021, 1 Comment

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  



Cambrian Period

 541-485 Ma   



Ordovician Period

 485-444 Ma



Silurian Period

 444-419 Ma



Devonian Period

 419-359 Ma



Carboniferous Period

 359-299 Ma



Permian Period

 299-252 Ma



Mesozoic Era

 252-66 Ma



Triassic Period

 252-201 Ma



Jurassic Period

 201-145 Ma



Cretaceous Period

 145-66 Ma



Cenozoic Era

 66 Ma-present



Paleogene Period

 66-23 Ma



Neogene Period

 23-2.6 Ma



Quaternary Period

2.6 Ma-present




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 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, 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    

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

What goes on a timeline of life? November 05 2020, 5 Comments

Suggestions for evaluating a timeline of life.

Spring cleaning in your biology closet March 04 2020, 0 Comments

It’s that time of year when the urge to put things in order can strike. You may have a closet with a lot of biology materials that you want to evaluate. Here are my suggestions for things to throw out. You may not want to discard the whole material just because it has flawed content provided it is feasible to fix the problems.

In the animal kingdom materials, if you find anything that has the phylum Coelenterata, please remove that name or cover it. Biologists haven’t used it for more than 30 years. That phylum was split into two others when biologists discovered that it held two unrelated groups. The two lineages are called phylum Cnidaria (anemones, corals, and jellyfish) and phylum Ctenophora (comb jellies). It is likely that you can cover over “Coelenterata” and add the label “Cnidaria.” Just make sure that you don’t have comb jellies in with your cnidarians.

Another no-no for the animal kingdom is showing protozoa along with the animals. This goes back to the two-kingdom idea of classification, and biologists and biology textbooks haven’t grouped protozoans with animals in more than 40 years.

If you find a chart that is labeled “Non-Chordates,” change the title to “Invertebrates.” Maybe “non-Chordate” was useful in the past, but biologists use “invertebrate” far more often. I searched books on using “non-chordates,” and I got six titles, all published outside the US. I searched “invertebrates,” and got over 6000 titles. A non-chordate chart isn’t likely to show current information, so it is time to recycle it or at least recycle the images and add new text.

The relationships between the phyla of animals solidified about 15 years ago. In biology, classification has morphed into systematics, which all about relationships and shared common ancestry. The details of this would take several blogs so I will simply say that the arthropods are related to the nematodes, and the mollusks are related to the annelids. Arthropods were once grouped with annelids, but that is no longer considered valid. Can you add something to your animal kingdom chart that shows which phyla are closely related? See my book, Kingdoms of Life Connected, for help if your animal kingdom chart needs a redo.  It is also available as an ebook (pdf).

Dig back into the cobwebs in the botany section of your closet. If your chart of the plant has club mosses separated from the fern clade – whisk ferns, horsetails, and ferns – you have a good representation of life’s diversity. The chart from InPrint for Children is a good example. . Another mark of a current material – it should use the term “eudicots” instead of “dicots.”  If your chart has phylum names, it is quite possible that many of the names are obsolete. Many botanists no longer use phyla or division names. Instead, they use lineage names, and sometimes a common name is all you need. I have a graduate level botany textbook that uses no phylum/division names. 

If your plant kingdom chart has fungi or bacteria on it, the time has come to do some serious pruning. Those two have to go to their own charts. If the image of a fungus appears on a plant kingdom chart, that’s what children will remember even if you say that it doesn’t belong there. The fungus kingdom is a sister to the animal kingdom. In nature, fungi and plants are partners, but on classification charts, they shouldn’t hang around together.

If you have a Five Kingdoms chart, file it under the history of biology. It should NOT be the first thing children see as they study the diversity of life. The Tree of Life is the place to start.

How about your timeline of life? This is a difficult material to do well, and there are many bad attempts out there. Does your timeline show several red lines coming together (converging)? That’s the traditional style, but lineages do not converge (fuse together); they diverge (split apart). Maybe you could salvage the images and redo the timeline without the misleading lines. Check the dates for the fossils because there are several in the wrong place on the older timelines.

Does your timeline of life have photos of extant animals or plants in prehistoric times? This gives a very wrong impression. I’ve seen a timeline that had “First marsupial” and a picture of a kangaroo. This is just like saying “First eutherian (placental) mammal” and showing a picture of a horse. Both the kangaroo and the horse evolved within the last few million years. They are both adapted to live on grasslands and open shrub lands, where resources are spread out, and there is little cover from predators. Therefore both are good at moving quickly over long distances. Neither one of them belongs in the Mesozoic Era on a timeline of life. Mesozoic mammals were much smaller and less specialized.

Does your timeline have the five major extinctions? And does it have ice ages in the right places? The older charts used ice to symbolize all extinctions, although that wasn’t the cause in most of them. The five major extinctions come at the end of the Ordovician, Devonian, Permian, Triassic, and Cretaceous Periods. They are such important shapers of life that they are essential to a good timeline.

If all this correcting sounds like too much to do, remember that you are doing it for the children. They need current information and a foundation that they can use in their future studies. There is no point in giving them science “information” that they will never see outside a Montessori classroom.

A suggestion for studies of the timeline of life October 20 2017, 0 Comments

The timeline of life is a vital part of cosmic education. It gives children a vision of how life has changed through time and an important perspective for appreciation of today’s life on Earth.

I have been frustrated with the many errors and misconceptions that are portrayed on the traditional Montessori timeline of life. Another material, not from the Montessori world, has come to my attention. It is from What on Earth? Books, . Author Christopher Lloyd and illustrator Andy Forshaw have done several “Big History” type timelines. These publications can give children a valuable framework of how life has developed and changed through time.

In order to show a variety of life and tie it into human civilization, the timeline uses different timescales across its length. This could lead children to a false picture of the time elapsed between the events depicted. You can help them understand the true duration of the various geologic time periods if you display the time periods to scale above the timeline in the What on Earth? Wallbook of Natural History: From the Dawn of Life to the Present Day

I did this for the 2.3 meter-long edition, published 2013. This book is 16.5 inches or 42 cm tall. I made a timeline that shows the true proportions of the geologic time periods. The second strip of paper beneath it shows the time periods as shown on the timeline. Here are the views from the formation of the Earth end and the present end. You can see that the Hadean Eon (black), Archean Eon (yellow), and Proterozoic Eon (pink) portions have vastly different shares on the two scales.

For example, the Hadean Eon is 31 cm long on the actual timescale, and 3.4 cm long on the timeline. The Cenozoic Era is 3.4 cm long on the actual scale, and the Holocene Epoch would be microscopic. On the What on Earth timeline, the Cenozoic Era is 46 cm, with 23.5 cm of that being devoted to the Holocene and Anthropocene. (If you would like the measurements for my two timelines, please email me.)

This timeline gives most of its length to the Phanerozoic Eon (Paleozoic, Mesozoic, and Cenozoic Eras), which is appropriate. The traditional Montessori timeline of life shows the events of the Phanerozoic Eon, even if it does not carry that label. When one looks at the What on Earth timeline from the end that shows the present, the Cenozoic Era has internal scale changes for emphasis on human events.

Nevertheless, I think the What on Earth timeline would be a good introduction to the changes in life through time. Having the life in the oceans shown separately from life on land helps children keep track of the two different environments. There are a few things you will need to correct/explain. The synapsid lineage is shown, but it is called “mammal-like reptiles,” an older term that paleontologists have dropped. Likewise, I would change the term “dicots” to “eudicots,” the term botanists use. Eudicots (true dicots) are the old dicots minus the magnoliids. At least the eudicots are there on the timeline, along with a good array of accurately portrayed prehistoric plants, a part that is often missing from timelines of life.

The What on Earth book or timeline is available in several sizes. There is a newer edition that is smaller and 6 feet long. You may need the magnifier, a flat, plastic Fresnel-type, that comes with the book, to read all the fine print. The timeline is available in a larger, 10-ft. edition as well. It is available on Amazon or on the What on Earth website. . It costs $40-50, and the smaller version costs $15-$20. At present, the nature (history of life) timeline is available in Japanese, Chinese, Korean, Taiwanese, American and Dutch. German, French, and Italian are in the works. The What on Earth Big History timeline is available in 15 languages, but the history of life takes up only about a third of it with human history displayed on the rest. See the What on Earth website of further information.

You may choose to make your own timeline. If so, my publication, Outline of Geologic Time and the History of Life, can help you. See .

Happy explorations of life through time.

The Tree of Life versus the Timeline of Life March 29 2017, 0 Comments

Someone has posted my Tree of Life chart on Pinterest and suggested in the caption that it could be a substitute for the Timeline of Life. NOT SO! These are two different materials with two different uses.

The Tree of Life does not show details of life through time. It shows extant animals and their lineages. People may be confused because classification has an element of time now. We group organisms by their common ancestors. You can’t show relatives without some reference to time. My cousins and I share a set of grandparents, so we have a recent common ancestor. That’s what makes us closely related.

Classification has become systematics (more on that in a later post). Biologists do not show rows of evenly spaced boxes with no connections when they diagram a kingdom or other related life. Instead, they connect the boxes (or names) with a branching diagram to show which organisms share more recent common ancestors.

The Tree of Life chart is used much like a Five Kingdoms chart was. If you are still using a Five Kingdoms, Six Kingdoms, or heaven forbid, a Two Kingdoms chart, you need to change to a different kind of chart. A Tree of Life chart is used to introduce children to the diversity of life. When I give this lesson, I tell children that this chart has a branch for all the major kinds of life on Earth. (And you may have one precocious child who asks “What about viruses?” No, they don’t belong on the organisms’ Tree of Life. They have their own.)

I can envision directing children’s attention to the big, black branches and noting that they are all connected, and they all share a common origin. I would also say that there are many, many varieties of life, and we would have a hard time studying it all at once. Instead, we put certain branches together for the purpose of focusing on them. Three of these major branches are called kingdoms because they are all the descendants of a common ancestor. They are outlined with color rectangles – yellow for fungi, red for animals, and green for land plants. The other two rectangles show organisms that we put together for the purposes of study – purple for prokaryotes and blue for protists.

The Tree of Life is used for children ages 6-9 to show them the big overview of life. They enjoy putting the cards on the solid, colored rectangles. The text on the back of the illustrations helps children place the picture of the organism. To help them find the right place, the major section and the name of the branch are in bold typeface. Older children and even secondary level students can still use the Tree of Life, and they should have an opportunity to place the cards and discuss this chart. Do they see that animals and fungi are sister kingdoms? This is why treating fungal infections is so hard.

On the other hand, the Timeline of Life shows the organisms that have lived during the time periods of the Phanerozoic Eon. A few timelines may have a bit of the previous Late Proterozoic, but the major emphasis is on life since the beginning of the Cambrian Period. There is nothing other than a timeline of life that can show this. Unfortunately the traditional Montessori Timeline of Life is riddled with mistakes – omission of the five major extinctions, all extinctions shown as ice ages, indistinct organisms, no grouping of related organisms, and my worst pet peeve, converging red lines that seem to show several lineages being fused into one.

OK, enough attacks on the Timeline of Life. It is still an important material for children, and I think it is important to use one that is updated and corrected, either by the teacher or by a company that has carefully researched its product. The Timeline of Life helps children understand how life has changed through time. (One last rant – add the Devonian explosion of plants! During that period, the land turned green as plants changed from a low green fuzz to trees that bore seeds. The Devonian – It’s not just for fishes!)

As a reminder of what is available on my website to aid you, my Outline of Geologic Time and the History of Life has lots of information that will help you make an accurate, up-to-date Timeline of Life. The Tree of Life chart is still a free download – my gift to the Montessori community. My book, Kingdoms of Life Connected, is a teacher’s guide to the tree of life. I updated it in the fall of 2016.

May you and your children enjoy exploring the living world, both its diversity and its history.