All of My Faults Are Stress Related

I’ve got one wallet-sized version of the 1983 Geological Society of America time scale in my field pouch, and another page-sized version that used to be taped to the wall in front of my desk. I relied on it a lot, especially when starting work in a new field area. In the early 90’s, when I was trying to break into the world of Appalachian tectonics research, I started by trying to figure out where the problems were in the models of how the metamorphic rocks of New England came to be. I spent a lot of time reading papers from different subdisciplines – the records of old mountain belts are partially recorded in the basins where eroded sediments collect, in volcanic rocks erupted before plates collide, in granites that intrude the deeper parts of the crust, and in the metamorphic rocks that tell how hot and how deep rocks were in the past. Some of those papers used fossils to tell time, some used radioactive isotopes, and some used complicated reasoning based on both stratigraphy and geochronology. Some of the papers told time using stratigraphic subdivisions: Emsian, Eifelian. Some used numbers: 390 million years old. Figuring out what happened when required a translation key, and the GSA time scale was a good one.

Lots of new radiometric ages of important stratigraphic boundaries, plus lots of discussions by the International Commission on Stratigraphy, have made my well-worn time scales obsolete. (Even by the mid-90’s, my paper copy had all sorts of notes about corrected ages of boundaries between periods.) And computers have made it easier to distribute color images. So now, more than 25 years later, GSA has a new time scale:


(GSA’s time scale web page, where updates will go, and where you can get your own copy.)

Some geobloggers will complain that this time scale is already out-of-date, because it includes the Tertiary (which has been abandoned, poor thing, by the International Commission on Stratigraphy). Personally, I’m glad it’s still there, because the old terms make it possible to read the old literature and figure out what it means. This is, after all, a translation tool – something that is needed so that paleomagnetists and stratigraphers and geochronologists and people who use all of their data can talk to one another. And I like the addition of periods like the Cryogenian – periods that I know about, but haven’t worked in, and don’t know ages of.

I’m curious what other people think of it. How about those colors? Is it confusing, the way that all four eras (Cenozoic, Mesozoic, Paleozoic, Precambrian) take up the same amount of space, even though the Precambrian is about 9 times as long as all the others put together?


  1. #1 Cameron
    March 26, 2009

    Thank you for the update. I just printed a copy off for my classroom.

  2. #2 Erik - Eruptions
    March 26, 2009

    Thats great! And I’m sure my student will love getting a shiny new time scale to learn as well. No, it is exciting to know that the timescale is dynamic, changing as we know more about the past. That is the way science is supposed to work, right?

  3. #3 APP
    March 26, 2009

    Sure, it’s confusing, to the uninitiated. There is way more detail than a non-majors intro geology class needs. I always show it to a class as an example of how complicated the whole system is, rather than as a tool for them to use.

  4. #4 clheiny
    March 26, 2009

    First Pluto, then the Tertiary. Which old friend will be next to face the nomenclature firing squad?

  5. #5 Bryan
    March 26, 2009

    Actually, it is out of date, in regards to the placement of the KT boundary.

    They are citing Gradstein et al. 2004, which places the KT at 65.5 Maa. However, Kuiper et al. 2008 have moved the KPg boundary (KT’s nom de plume)to 65.95 Maa.

    For most people, this is irrelevant. Unfortunately, every time somebody changes the dates of this particular boundary, it means I have to go through my latest draft and find all the places where I cite a date for the the KT transition and change it. It’s more annoying than any other aspect of my thesis.*sigh* I might have to change it around…. again. The lesson I am learning is NEVER work with a “famous” boundary.

    I really sympathize with this quote:
    “Let us make an arbitrary decision (by a show of hands if necessary) to define the base of every stratigraphical unit in a selected section. This may be called the ‘Principle of the Golden Spike’. Then stratigraphical nomenclature can be forgotten and we can get on with the real work of stratigraphy, which is correlation and interpretation”.
    — Derek Victor Ager
    The Nature of the Stratigraphical Record, 3rd ed. (1993), 110

  6. #6 Acipenser
    March 26, 2009

    Ooh, shiny.

    On the Precambrian: I don’t feel it deserves more space now. What would you put there? I don’t know, and I study it. Keeping it (relatively) simple makes life easier for both us Precambriates and those ex-Tertiaryites.

    And I do agree that one needs to keep tertiary there, at least for a while. At least half of the literature still refers to it.

  7. #7 Kurt Friehauf
    March 28, 2009


    Your link to the GSA site full resolution graphic is

    The “t” at the end of the file name indicates this is the thumbnail image and not the full size graphic.
    The correct link should be:

    Thanks for the tip!
    I hope all is well with you.

  8. #8 Ian
    April 3, 2009

    About time!

  9. #9 Lab Lemming
    April 4, 2009

    Dude, those are Ar/Ar years. Use a real isotope.

  10. #10 Kim Hannula
    April 4, 2009

    I would get all defensive about insults to the only isotope system that I’ve used, but based on my experience… well, I don’t use argon dating any more. At least not on metamorphic rocks.

  11. #11 Wayne Ranney
    April 11, 2009

    I like the color! The idea here is possibly to make the time scale easy to use (and to attract the younger crowd – a good idea I think).

    One quibble – I wish they would have used the blue color for the Pz and green for the Mz. That is traditional.

    The Pc may be a long time period but no need to highlight that concept in here.

    I’ve been using the 2004 time scale from Canada Natural Resources and love it! Cheers.


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