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Q: How can I convey the very long times involved in the history of the Earth and life on Earth?

Science and Children—July/August 2023 (Volume 60, Issue 6)

By Matt Bobrowsky

Q: How can I convey the very long times involved in the history of the Earth and life on Earth?

A: It can be very difficult for children to understand long expanses as time. Do they even have a sense of how long it’s been since they were born? A student might know that she is eight years old, but does she really have a feeling for how long that is (especially considering that her memories might go back only to age four—half of her current age). To help students understand long periods of time, it can be useful to introduce them to timelines.

We can think of a timeline as a kind of model. Just as a model car is a scaled-down version of a real car, which shows where all the parts are, a timeline is a scaled-down version of a (usually very long) period of time. In this case, the “parts” are various events that occurred at certain times in the past, or will occur in the future, which we can mark on our timeline.

Make a Timeline or Two

Students will find it easiest if they start with short timelines, and they will be most engaged when events in their lives are included. A simple way to start is to help students make a one-day timeline covering the past 24 hours. They can make, perhaps with a ruler, evenly spaced marks on the timeline labeled with the hours (or every two hours). Ask them to mark on their timeline everything they do at the same time each day. So, for example, they might wake up at 7:00 AM, eat breakfast at 7:30 AM, go to school at 8:00 AM, and so on. From the previous evening, they might eat dinner at 6:00 PM, go to bed at 9:30 PM, etc. They can add other, informative graphics to their timeline, for example, shading in the part of the timeline when they’re asleep, and they can add some art (going from STEM to STEAM), drawing a small picture of each event. When they are finished, they will have essentially modeled a period of time with an actual line on a piece of paper—a timeline. See the example in Figure 1. Note that all of the timelines in this article are drawn vertically—so they’ll fit better into the columns of the article—but your students’ timelines can be either vertical or horizontal. Find links to high-res versions of these timelines under Online Resources.

Figure 1
Example of a 24-hour timeline.

Example of a 24-hour timeline.

Next, each student can make a line that represents a much longer period of time: their lifetime. It can run from birth just up to the present time, or it can extend into the future, showing that a timeline can illustrate both past and future events. Perhaps there are some things they are planning to do in the future? The evenly spaced marks on this timeline will not be hours, but years (possibly with individual months as well). Notable dates could include birth, first memory, starting school, etc. See the example in Figure 2. Older students will usually be able to predict or plan events farther into the future than younger ones can.

Figure 2
Example timeline of a student’s life.

Example timeline of a student’s life.

For either of those first two timelines, you, dear teacher, can provide an example for students by making your own timeline on the board, so they can see how it works. Students will love hearing about what you did for the past 24 hours or about major events in your life. After students have made their timelines, they can answer questions like, “Do you spend most of a day awake or asleep?” If they’ve learned about fractions, you can ask them to estimate what fraction of each day they’re asleep (usually about 1/3). Looking at their timelines, they can answer questions—without doing any subtraction—like, “How much time goes by between breakfast and lunch? Between lunch and dinner?” and “So far, was more of your life spent (i.e., more years) before starting school or after starting school?” For students in grades 1–3, more of their life so far has not been school, although, students of all ages won’t have many memories from before starting (pre-)school. Students can take their life timelines home with them and ask parents to help them add additional events in their life, such as when they first started to walk, first started to talk, and so on. You can imagine the fascination a student will have with a timeline of her/his own life. And parents will enjoy talking to their children about things they did when they were younger.

Longer Timelines

Having made those first two timelines, students can now see that a line on a piece of paper can represent any amount of time. Could it represent the past 2000 years? Yes! The older your students, the farther back in time you can reasonably discuss. For a 2000-year timeline, the evenly spaced marks on the line might represent intervals of 100 years. So, you can discuss—and students can mark on their timelines—a few of the STEM milestones that occurred in many of those centuries (see Table 1).

Origin of Dinosaur Names

Most of our English words have their roots in other languages. In the word dinosaur, the dino part comes from a Greek word meaning “monstrous,” and the saur part comes from a Greek word meaning lizard. So a dinosaur is a scary lizard!

In the word Stegosaurus, the stego part comes from a Greek word for “roof” or “cover.” Why was it named a “cover lizard”? Because it’s covered with bony armor and a row of bony plates down its back.

Table 1
Selected STEM events from the past 2,000 years.

Selected STEM events from the past 2,000 years.

We can make timelines that cover even longer periods of time, even millions or billions of years. Let’s take a look at the timeline of life on Earth shown in Figure 3. There are a lot of interesting things to see. For instance, humans have been around only a very tiny amount of time compared to the dinosaurs’ reign on Earth. Anatomically modern Homo sapiens—humans that look like us—had evolved by at least 130,000 years ago. Compare that to the 165 million years that dinosaurs roamed the Earth—over a thousand times longer than humans have existed thus far.

Figure 3
Timeline of life on Earth. Major time divisions are  50 million years apart.

Timeline of life on Earth. Major time divisions are 50 million years apart.

Different species of dinosaurs lived at different times, often separated by tens of millions of years. There was no single time—no “age of the dinosaurs”—when all the different types of dinosaurs lived together. An interesting fact, which you can see from the timeline in Figure 3, is that we are living closer in time to the Tyrannosaurus rex than the T. rex was to the Stegosaurus. We humans are separated from the last T. rex by 66 million years, but the T. rex appeared more than 90 million years after the last Stegosaurus. And that doesn’t even take into account the even earlier dinosaurs from the Triassic period, which are almost twice as more distant in time from the T. rex than the Stegosaurus was. So, was there really a single “age of dinosaurs”?

An aside—If you’ve read the sidebar about dinosaur names, this might make sense: I am writing this article on Coronation Day for Charles III. As a British king, could he be referred to as a “tea rex”?

Never stop learning.

Online Resources

Figure 1: Example of a 24-hour timeline.

Figure 2: Example timeline of a student’s life.

Table 1: Selected STEM events from the past 2,000 years.

Figure 3: Timeline of life on Earth. Major time divisions are 50 million years apart.

Matt Bobrowsky is the lead author of the NSTA Press book series, Phenomenon-Based Learning: Using Physical Science Gadgets & Gizmos. You can let him know if there’s a science concept that you would like to hear more about. Contact him at


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