Initial Publication Date: February 8, 2012

### Erika Grundstrom, Physics & Astronomy Department, Vanderbilt University and Physics Department, Fisk University

Since I began teaching about astronomy as an undergrad, I've felt that understanding long timescales are extremely important and especially to the fields of astronomy, biology, chemistry, geology, and anthropology – if students were able to grasp a bit of how LONG the Universe (and Earth) had been around, it would help them understand why the world is the way it is. It also might help some understand a bit more about their religion and science. But if you were to talk about "Deep Time" to an astronomer, you would get a much different timeframe than if you were talking to any of the other scientists. While it is very difficult to conceive of the vast timescale of Earth, the lifetime of the Solar System is only one‐third of the lifetime of the Universe. As far as actually teaching about long timescales, often I focus first on distance scales rather than time scales – there is no larger distance than an astronomical distance!

One advantage to this technique is that I have found that once students start thinking about how much bigger distances are than they thought, they are more ready to start thinking about how much longer time spans are than they thought. Another advantage to this technique is that students don't have the cognitive load of trying to figure out BOTH a time scale and a distance scale (like trying to put a timescale on a football field).

But if we take away a cognitive load of scaling and equating time and distance and put it toward equating time with time, we come up with the major tool in my timescales arsenal: "The Cosmic Calendar." Popularized by the amazing astronomy explainer, Carl Sagan, the Cosmic Calendar compresses the entire timescale of the Universe into one year. During the class period, I have the students write down our events on PostIt notes, put them in the correct order (sometimes quite debated!), then guess which dates they will occur by sticking the notes up on my huge PostIt notes on the wall. Then we look up the correct times and do ratios and converting to find the correct days of the year. The Wikipedia article on the Cosmic Calendar does an excellent job explaining this construct and has excellent graphics. Despite the time we spend on these exercises, perceptions of both time and distance scales are not accurate (according to little surveys I do and some test questions). But they are more accurate than before we did the time and distance scale exercises. Part of the reason I want to attend this workshop is to learn about techniques that others use and assessments that people use to help see if their students are grasping the concepts.

A small assessment and an interesting bit of research that I did in the past was to give a short online survey to online university students asking them to order nine events on a football‐field timeline:
1. Earth formed
2. Most recent Ice Age
4. Big Bang
5. First humans walked on Earth
6. Dinosaurs died
7. Universe formed
8. First life on Earth
9. Sun formed
They were to enter numbers in the given order.

We had twelve respondents but they seem to be in line with what we already know from previous studies from geoscience research. A table with the results and a plot of the results are given below. We did find that the order in which we asked the events (shown above) seems to have affected the values a little – being asked when Earth formed and then when the Big Bang happened a few rows later did not always make for consistent answers.
Trends we noticed:
• All students agreed that the Sun formed before Earth and that life appeared after Earth formed (correct)
• Almost every student believed that the Sun formed well before Earth (incorrect)
• Most students stated that the Universe began before the Sun formed (correct) but that the time between the beginning of the Universe and the formation of the Sun was quite short (incorrect)
• Some students believed that time began well before the Big Bang/Universe formed and that the Big Bang and the Universe forming did not happen at the same time (both incorrect)
• Even if the times were scaled to Earth's formation is zero yards and now is 100 yards, students still don't have an accurate perception of the timescales (they think that life appeared later than it really did and that everything else happened earlier than it really did) ‐> see the tiny figure on page 3
These results are in line with other studies but especially in line with a study looking at temporal scales on all levels (VERY short to VERY long) by Lee et al. (2011) (also see their references – they discuss many of the relevant papers). They concluded (among many things) that students may have a logarithmic timescale in their heads.

References:Cosmic Calendar. (2011, December 12). In Wikipedia, The Free Encyclopedia. Retrieved 04:05, February 3, 2012, from http://en.wikipedia.org/wiki/Cosmic_Calendar

Lee, H.‐S., Liu, O. L., Price, C. A. and Kendall, A. L. (2011), College students' temporal-magnitude recognition ability associated with durations of scientific changes. Journal of Research in Science Teaching, 48: 317–335. doi: 10.1002/tea.20401

Table and Figures:
Table: Results of an assessment asking students to order nine events on a football‐field timeline. Click image to enlarge.

Figure 1: All events. Click image to enlarge.

Figure 2: Just geological timescale events with Earth's formation being the zero point (same color schemes) Click image to enlarge.