Geologic Time
For the past couple of weeks, kids in Indigo band have been working on a massive timeline of Earth’s history, to scale. There are no real of examples of this for us to follow as the amount of time we need to show is simply too massive. Most geologic timelines compress the actual length of eons, eras, periods, and epochs into legible lengths, but this doesn’t give students a sense of just how old the earth is. Other more complicated models show a zoomed view of the latter parts of the timeline, which, while accurate, can be confusing. After introducing the idea and polling the kids about how long they think it should be, responses ranged from “uh, a sheet of paper” to “maybe the length of the board?” and so on. After doing some calculations, the kids quickly realized that a timeline of this scale would be mostly unreadable. After some more discussion, I proposed that the shortest chunk of time, the Holocene Epoch, should be no shorter than a centimeter. Once we had that, we could work backwards to determine the length our timeline needed to be.
After some careful calculations, we determined our timeline should be a whopping 192 pages long. That’s 2,112 inches or 176 feet. Where do you put something that big? After discussing some options, we settled on the walls around the office. If we snaked the timeline around, we could make it fit. 
Since we know our length and our base unit (1cm = about 850 thousand years) we could then start the task of figuring out how long each eon, era, period, and epoch could be in centimeters. We created a massive spreadsheet that held all the information we would need for the project. By filling in the time period start and end dates, the kids found the duration of the period. Once we had that, we could divide it by our unit rate (850 thousand years) and figure out how long it would be, but that was also only partially helpful. Since we were using sheets of paper to build our timeline, we had to convert the duration of each time period into pages. To do that, we needed to know how many millions of years could fit on the length of one sheet (about 23 million years), which left us with a number of pages and an awkward decimal. Since it’s impossible to accurately cut 0.2634 of a sheet of paper, we then had to convert the decimal to centimeters so we could measure out the last bit. Whew.
To the delight of the kids, we only did this a few times to make sure they got the concept, then I showed them how to make Google Sheets do the magic for us by repeating the same calculations down our chart of data. Next came the tedium of actually building this thing, which I admit was a bigger behemoth than I anticipated. The kids rotated through jobs like a factory. One student would count the number of sheets needed and hand them to the next person, who would label the sheets with the name, type, and length of that time chunk. Next, the stack would go to the cutter, who sliced the sheets down to size, finally, it would go to the tapers who attached the sheets into strips. While this was happening, a group of kids worked on assembling the timeline on the wall.
After a few work sessions, the bulk of the earlier work was done. All that was left was to hang the pieces and creating a display board to explain the timeline. Today, the kids worked in 40 minute shifts in teams of three, hanging or labeling the time chunks on the wall. While they were working on the timeline, the other kids were researching timeline events to put on the wall. The kids are researching landform changes, tracking the drift of the continents, following the evolution of life (plants and animals), tracking sea level changes, and events happening in California throughout geologic time. As I write, we have a COMPLETE timeline on the wall and only need to finish the labels and add the research. I’m so proud of the perseverance my band had shown even though this project has only gotten bigger and bigger throughout the Arc.
