When the hell are we?

Whenever you’re trying to talk about science to a broader audience, one of the major challenges is cutting out the jargon. Sometimes, though, the real difficulty is not so much in translating the jargon, as identifying it in the first place. This problem his highlighted by BAllenJ’s comment on my last post:

…when you write these geology posts that the non-geologist can enjoy, could you please use the age instead of the geological name, or even better…along with? I need a secret decoder ring (OK, answers.com) to decode stuff like “During the Cretaceous and early Cenozoic…”

He’s absolutely right, of course. I’ve discussed in previous posts the whys and wherefores of the geological timescale – how it attempts to divide geological history up into distinct chunks, each with its own unique tectonic, climatic and biological character. For geologists, it’s a useful shorthand, because we’re familiar with the geological timescale and know more or less where all of the different periods slot in*. I suspect that talking about named periods rather than absolute age ranges also helps geologists to handle the disconnect between the lengths of time we’re discussing when talking about Earth history (tens, hundreds, and even thousands of millions of years), and the lengths of time that our little primate brains can actually get our heads around (ranging from a handful of years down to seconds, depending on how cynical you’re feeling). Regardless, we’re so used to bandying about ‘Cretaceous’ and ‘Cenozoic’ that we forget that they can be, to the layman, words just as impenetrable as ‘diagenesis’ or ‘turbidite’ (or, indeed, ‘allochthonous‘).
I’m not unaware of this problem, of course, and at a number of places in that post I did provide numerical ages as well as period names. But I didn’t everywhere, partly because I simply forgot to, but also because it’s sometimes difficult to do so without destroying the flow of the text. Also, I’m not entirely convinced that simply inserting the numbers always helps people to really get to grips with where (or when) the hell I’m talking about. Perhaps it would just be easier to show visually when I’m talking about:


This is actually an idea I’ve been toying with for some time, but just hadn’t got around to implementing: place this compressed timescale at the bottom of the post, with the red bar showing the time period I’m talking about, and every time I mention a geological period name, internally link down to it. I’ve just given ‘Tectonics shown to drive changes in biodiversity’ this treatment. Take a look, and let me know whether you think this is a useful addition, or whether I should just stick to adding more numbers. I am a little worried that the text is a little too small, or the logarithmic-esque timescale required to fit everything on nicely might be a little bit confusing. But it’s fun to play…
*Of course, even we geologists usually have some shaky areas; as Christie has commented in the past, coming to South Africa gives you a whole new perspective on a period of Earth history which was previously generically filed away under ‘really old stuff’, or ‘that time before multicellular life kicked off’.

Categories: deep time, general science, geology

Comments (19)

  1. ScienceWoman says:

    This is a brilliant idea!

  2. christie says:

    This reminds me of studying for the AP US History test in High School – my little brother the history buff helped me break it down into presidential administrations (44 units is much more than the geologic time scale) … but the same concept applies… a date is just a date, but if you say Devonian, you can impart a picture of a period, associate it to other events (the “age of fishes”), etc.
    The classical time scale was biostratigraphic, so dates were not known, only associations with other fossil assemblages of a certain age. That’s where the ‘jargon’ originates… and in many cases, where radiometric dates are not available, that’s still as good as it gets…

  3. Kim says:

    I like the visual time scale.
    One problem with giving the number (especially for stratigraphically constrained ages) is that those darn geochronologists keep changing the ages of the boundaries between some of the geologic periods. (Maybe it has settled down now, but most of the ages that I memorized are now wrong. Frustrating, especially because I have enough trouble remember my phone number. I have a habit of giving ages on the 10′s to 100′s of millions of years time scale when I talk in class, in part because I can’t remember the exact ages of most geologic events.) It can really confuse people if they think of the numerical age as the real one, when the name “Cretaceous” is the part that doesn’t change.

  4. Scott Belyea says:

    place this compressed timescale at the bottom of the post, with the red bar showing the time period I’m talking about

    Great idea. I guess I’m a reasonably literate layperson, and I do have some associations with a few of the period names. However, I don’t use them much and they don’t tend to come up in my day-to-day conversations; as a result, I’m a bit hazy sometimes on the relationships or the numbers.
    BTW, this is a very good example of what can easily be done on-line but has no good analogue on paper.
    Get ScienceBlogs to make it mandatory, would you?? :-)

  5. Ian says:

    I like the visual time scale too….
    As an interested, very amateur, follower of blogs such as yours (which I like very much) it can be very confusing to follow some of the basics – such as Geological Time.
    So the small explanation timescale as demonstrated is a huge help.
    Please include in future, but most importantly – keep posting. Even the 50% I understand is fascinating.

  6. It is a wonderful idea, especially for people like me. My dad was (is) a geologist (worked for the National Park Service as a Park Ranger) and used to lecture on family vacations regularly. The problem is, he uses the nomenclature from the early 1960s and things have changed. For instance, what the hell happened to the Precambrian?

  7. chezjake says:

    An excellent idea. I approve heartily.
    For newcomers to the blog, you might also set it up to automatically provide a link back to your original explanatory post.

  8. arby says:

    Great idea. rb

  9. Kevin says:

    It’s a good idea. One thing though – is it just me, or do other people see this scale as “backwards?” My intuition is that the “beginning” is at left end of the X-Axis, with time increasing to the right. To me, the scale makes more sense if -4 (4 billion years ago) is at the left, with “today” (0) on the right.
    I did a quick web search to see if there was some consensus on this – most of the charts were up/down instead of left/right! The few left/right ones I saw did it “my way.”

  10. PaulG says:

    FAO Billy. I think you’ll find that Chris is living on it at the moment.
    I say pre-Cambrian, although admittedly not very often, as I work mainly in the Carboniferous (about 300-350 million years ago).
    Chris – good idea.

  11. Scott Belyea says:

    One thing though – is it just me, or do other people see this scale as “backwards?”

    I’m with Kevin. Graphs with a time scale usually have later dates to the right. This isn’t really a graph, but it’s close enough that it took me a couple of seconds to get oriented.

  12. coconino says:

    It gets a little more complicated when you start throwing in terms like “Neogene” which is a period covering the Miocene thru Pleistocene epochs. If you’re working in North America, the Carboniferous is broken down to the Mississippian and the Pennsylvanian.
    In the above scale it would help to have eons, eras, periods, and epochs labeled. It would help to answer (((Billy)))’s question regarding Precambrian, which is a supereon comprised of the Hadean, Archean, and Proterozoic eons.

  13. BrianR says:

    This is a good idea … Chris, maybe you can upload a version for other geo-bloggers to use?
    As for the direction … I like the present being on the left, but it doesn’t matter too much I suppose.

  14. Kim says:

    Yes, Chris, if you’re willing to share, I would love to use this too.
    (And when I draw horizontal time scales on the chalkboard, I always put NOW on the left, and get older towards the right. Geologists tend to have weird sign conventions. Older = positive numbers. Down also is positive. Drives physicists and engineers batty, and causes problems with sign conventions for stress.)

  15. Divalent says:

    What’s wrong (or obtrusive) about using a parenthetical after a geologic age? Seems to me it would be easier for those of us that don’t yet have the conversion algorithm hardwired in our brain to follow the flow of the post.
    Example “These rocks date from the Carboniferous (~325 mya) and were layed down …”.
    The chart would be better than nothing for us GeoChronoIdiots, but it does leave us a bunch of busy work: we’d have to leave the text and hunt for the chart whenever an era name is used, then hunt again to find our place back in the text.
    Plus, with time, the continual pairing of the era and the numeric age just might just drill the algorithm into our skulls.

  16. Chris Rowan says:

    Well, the consensus seems to be that this a good idea. Good! And yes, I don’t mind sharing at all – I’ll sort something out later.
    As for the direction of the timescale, I think having the present as the origin is pretty standard in most geological plots, but maybe I’ll try reversing it if people think that looks better. Of course, it might also be something to do with me being left-handed, in which case I might have to take a stand against dextralist oppression…
    Divalent – as some of the other commentators have pointed out, the ages of the different periods have drifted a bit over time (I seem to recall the base of the Cambrian shifted by ten million years or so some time in the last decade), although we seem to be asymptotically approaching some sort of stability as dating accuracies have improved. There’s also the issue that saying ‘~325 million years’ might give a false impression of accuracy, when often we can only date events to, say ‘between 300 and 350 million years ago’. There’s nothing to stop me saying that, of course; I guess I’m thinking of this little figure as more as an augmentation than a replacement, and it helps to place the stuff I’m talking about in the wider context of the Earth’s history.

  17. Divalent says:

    Sorry, not to be a butt about this (the chart will be an improvement, so I’ll let it slide after this last vent), but …
    1. I’ll just point out again that to use the chart you have to break away from the text to consult it, then find your place again. And unless the text has telegraphed that I need to have the date in my mind to make sense of what follows, I’m liable not to consult it until I find myself confused or uncertain.
    2. “~” (I thought) was a universal indicator of approximate.
    and to clarify my suggestion:
    3. If refering to the whole era, then “Carboniferous (~300-350 mya)” would be appropriate, whereas …
    4. If refering to a particular dated rock that you are noting the era of (which is the situation I had in mind in my example), where an actual (approximate) date was determined for the rock, then the example I used would be appropriate (“These rocks date from the Carboniferous (~325 mya) …” assuming the estimated date of the rock was ~325 mya).
    I’ve read lots of geology and paleontology-related books (from the “popular” up to things that approach technical) and every one has a diagram inside the front or back, and maybe its just me, but I find it just doesn’t stick (probably because I am not forced to think about it in my daily work). [Off the top of my head, I couldn't tell you the chronological order of the carboniferous, pennsylvanian and mississipian eras (although I am more certain than not that each is an actual named era)].
    I’m just sayin’ …

  18. KC says:

    “I suspect that talking about named periods rather than absolute age ranges also helps geologists to handle the disconnect between the lengths of time we’re discussing when talking about Earth history…”

    I know at least for me, I’ve already formed associations with the timescale. An absolute date really doesn’t mean anything to me until I translate, for example, 75 Ma limestone into ‘Cretaceous chalk’, and then I go ‘aha!’… The picture forms in my mind and I get a relevent sense of that part of the Earth’s history and how it relates to other parts.

  19. themad don't-know-much-about-geology lolscientist, FCD says:

    Graphic timeline FTW!