Controversies in the Earth Sciences

Antipodes and geologic time


How to comprehend deep time

In the activity below, the whole class will work together to make a representation of the geologic timescale. The way we'll do this uses the concept of antipodes. The antipode is the opposite point of any point on the surface of the Earth, so that if you connected the two points with a line through the center of the Earth, that line would be an exact diameter. Mathematically, the antipode of a point whose latitude and longitude are (A,B) equals (-A, B ± 180°).

As an example, the latitude and longitude for State College, PA, is

40.8° N, 77.9° W

Its antipode is 40.8° S, 102.1° E, as shown on a map of where this is located.

As you can see, when my children get in the sandbox, they are not digging a hole to China. They are in fact digging a hole to the Southern Indian Ocean off the west coast of Australia.

two boys in a sandbox

Having trouble visualizing antipodes on a sphere?

Here's an animation of an antipode using Eliza's Cherry Skewer Mental Model (Click to download)

Try This!

Calculate the antipode of your home town. Here is a good link for looking up the latitude and longitude of many locations in the world: Get Latitude and Longitude.

What does this have to do with the geologic timescale?

Our planet is approximately 4.55 billion years old. It is a challenge for any human being to comprehend just how long a billion years is. This is one of the reasons that many people have trouble accepting the fact that biological processes such as natural selection can work. How can we try to represent the age of the Earth in a way that people will really understand what a billion years means?

Antipode and Timescale Problem Set

In this activity, we'll use distance as a proxy for time. Penn State's campus at University Park, PA (in State College) will represent the present time, and PSU's antipode will represent 4.55 billion years ago when the Earth was formed. The great circle distance between PSU and its antipode then represents 4.55 billion years.

Part 1

Save the Antipode and Timescale Worksheet to your computer. Use that word processing document to record your work.

  • Save the worksheet to your computer by right-clicking on the link above and selecting "Save link as..."
  • The worksheet is in Microsoft Word format. You can use whatever word processor you like to work on it. I can read most formats but check with me if you use something unusual.

Record your answers to the following questions on your worksheet:

  1. Calculate the great circle distance between PSU (40.8 N, 77.9 W) and its antipode (40.8 S, 102.1 E). What is this distance in kilometers? **If you don't remember how to calculate great circle distance go back to the tsunami travel time problem set fromLesson 2 and review it.
  2. The distance between PSU and its antipode is half the circumference of the Earth, and in our model it corresponds to 4.55 billion years. How many million years is 4.55 billion years?
  3. In this model, calculate how many kilometers correspond to one billion years. How many kilometers correspond to one million years in this model?
  4. Calculate the great circle distance between PSU and the city where you were born. What is this distance in kilometers?
  5. How many years prior to the present time does this distance represent? (Remember that the location of PSU corresponds to the present time in our model.)
  6. Calculate the great circle distance between PSU and somewhere else of your choosing (e.g., where you live now, or the best place you ever visited, or a place you want to go). What is this distance in kilometers?
  7. How many years prior to the present time does this distance represent?
  8. Using the geologic timescale, what is the era and period corresponding to each of your two points in time?

Submitting your work

First, add your data to our class table in Canvas. My data is given as an example. Next, save your worksheet as a Microsoft Word, Macintosh Pages, or PDF file in the following format: Antipode_AccessAccountID_LastName.doc (or .pages or .pdf). For example, Cardinal starting pitcher Adam Wainwright's file would be named Antipode_apw50_wainwright.doc

Upload your Antipode Worksheet to the Antipode and timescale problem set part 1 assignment in Canvas by the end of the first week of this lesson. I will check your work so that you can make any corrections to the class table if you need to before Part 2 is due. Part 2 will be due a week later (the end of the second week of this lesson).

There is a week in between the due dates of part 1 and part 2 of this assignment so I can check part 1 and have you make corrections if necessary. Meanwhile, go on and do the reading assignments / discussions on the following pages, then come back here to finish part 2.

Part 2. Make your own geologic timescale

I want you to make a geologic timescale in which the dimension of time is measured consistently at a single scale. The two pdf files of the timescale produced by GSA and the USGS linked from page 3 of this lesson are made the way they are because the authors wanted each named portion of time to be legible, and they wanted to produce something that more or less fit on a page. This is instructive, but it can be misleading because periods of time closer to the present time are given more space. For example, see in the USGS timescale how the Holocene epoch (in which we now live) is given approximately the same amount of space as the late Jurassic. The Holocene is about 11,500 years long and the late Jurassic lasted about 15 million years. So, obviously, we are distorting time in favor of the present. Let's have a little humility and make a model to scale.

It is not as easy to appreciate the vastness of time before anything cool (like life!) began on this planet unless you can see what the timescale looks like when it is drawn to scale, so that's what we'll do next.

  1. Choose a scale that makes sense to you and allows you to fit your timescale on one 8.5" x 11" page. This means you must come up with a scale that will fit 4.55 billion years into something less than eleven inches. Keep in mind that you are not being asked to recreate the standard issue geologic time scale as they are rarely created with a consistent time scale. HINT: The easiest way to do this will be to draw your timescale on graph paper. You can make your own graph paper on line for free and print it out at Incompetech Inc.


    You will need to submit your timescale electronically. It is okay to draw your timescale by hand and then scan it. Or, draw your first draft of it by hand and then make an electronic version of it. If you scan something that you have drawn by hand, please check for legibility before submitting it.

  2. Include the following dates on your timescale:
    • origin of the Earth
    • present time
    • Permian/Triassic extinction
    • Cretaceous/Tertiary extinction
    • beginning of the Cambrian
    • each class member datapoint from the table in Part 1
  3. Include the following time periods on your timescale:
    • Paleozoic era
    • Mesozoic era
    • Cenozoic era
    • Holocene epoch
  4. Save an electronic version of your timescale as a Microsoft Word, Macintosh Pages or PDF file in the following format:

    Timescale_AccessAccountID_LastName.doc (or .pdf or .pages).

    For example, Cardinal outfielder Dexter Fowler's file would be named "Timescale_wdf25_fowler.doc"

Submitting your work

Upload the electronic version of your timescale (from Part 2) to the Antipode and timescale problem set part 2 assignment in Canvas by the end of the second week of this lesson. NOTE: The timescale (part 2) is due a week later than the antipode worksheet calculations (part 1). This is because you will need the data your classmates provide in Part 1 to complete Part 2. You are probably wondering why I've repeated this fact about four times now. Just to see if you're still reading! No, but, really, I've had somebody get confused about this every time I've taught this class, I swear.

Grading rubric

I'll use my general rubric for grading problem sets to grade this activity. I made each half of this problem set worth 50 points so together they'd add up to the usual 100 points.