Green Gabbro

Let’s get one thing out of the way right now: The question of whether or not a new geologic epoch has “really started” is precisely as stupid as the question of whether or not Pluto is “really” a planet. The definitions of geologic eons, eras, and epochs are not objective truths about the history of the planet that are simply waiting for us in the rock. The geologic time scale is made up by geologists, for geologists as a matter of convenience. So Greg Laden is making a category error when he dismisses both the Anthropocene and the Holocene as scientifically invalid – the worst thing you can really say is that they’re inelegant.

Okay, the Holocene is inelegant, and the Anthropocene is unbearably narcissistic. What does that mean to our future cockroach geologist overlords? And am I really going to argue that the geologic time scale is racist?

When constructing a geologic time scale, we try to align its divisions with what we think are important changes to the character of rocks and fossils, and we want to be consistent about mapping big changes to big divisions and little changes to little divisions. We also want to set up a time scale that is useful for scientific communication among geologists, so we try to reflect the divisions and terms in actual use.

This is where we can get into trouble. For example, in North America, sediments from 360-320 million years old are mostly limestones which outcrop in the Mississippi River Valley. Sediments from 320-300 million years old, by contrast, form many of the coal mines in the Eastern U.S. To reflect what seemed to be a natural division, North American geologists divided these rocks into the Mississippian and Pennsylvanian periods. Meanwhile, Western Europe from 360-300 million years ago was one long unbroken organic-rich sediment deposition machine, so European geologists simply called that period of time the Carboniferous. Eventually, the geographic peculiarities of North America were enshrined in the time scale as the Mississippian and Pennsylvanian sub-periods of the Carboniferous. If there are natural divisions in the Carboniferous stratigraphy of Asia, Africa, Australia, or South America, we don’t see them in the time scale because racism colonialism geologists from those continents did not have much influence when the time scale was first put together.

Regardless of its place within our preferred metanarrative of time, the Holocene exists because it has a practical purpose. Of course, many of the Holocene’s charms are restricted to temperate latitudes: if you live in an area where the most recent Ice Age cycle crapped all over your landscape, then of course you will want to draw a line at the place where “glaciers ate my homework” is no longer a plausible excuse.

I have to admit, I’m partial to the Anthropocene. If we adopt it, though, we leave the Holocene looking not just inelegant, but so enfeebled as to be utterly useless. At 11,000 years long, the Holocene would be ten times as short as the next-longest Cenozoic epoch, the Pleistocene – which, at 1.8 million years, is piddling short in its own right. Plus, the Holocene looks much like any other Pleistocene interglacial period. Wooly mammoths, saber-tooth cats, and giant sloths may have gone extinct near the base of the Holocene, but even though they were awesome, I don’t think they were widespread enough to make good index fossils. There is absolutely no way such a piece of crap epoch as the Holocene will survive the scrutiny of our future cockroach geologist overlords.

So assuming that cockroaches prefer to see Earth history as a series of distinct periods rather than as a continuum, will they lump the Holocene in with the Pleistocene, or with the Anthropocene? My bet is on the Pleistocene – the changes to atmospheric chemistry, climate, and sedimentation pointed out by Zalasiewicz et al., and the spread of uniquely anthropogenic fossil markers (beer bottle caps), are all global phenomena whose geologic record will be readily accessible, making the Holocene-Anthropocene boundary a very good candidate for a golden spike. If it turns out that cockroach geologist children are reeeeeeally enamored of the Pleistocene megafauna, though, all bets are off.

Comments

  1. #1 Greg Laden
    February 1, 2008

    I am pretty sure that we are in agreement on the general points here, but it is not correct to say that I’m making a category error when I suggest that the Holocene is “invalid.”

    It is invalid for two reasons. One, it does not do what you say geological time units should do. Its beginning is placed at an arbitrary date on which nothing happened. Two, by any definition of the Pleistocene, the Holocene is part of the Pleistocene, as you suggest it should be.

    So, by your reasoning the holocene is more than inelegant.

    As I have said over at my place, it does not matter. Yes, these various time units have some degree of meaning, but the meaning of the meaning also shifts as we move about in time. But, as with archaeological periodization, geological periodization can be as much a product of history of the field as anything else, and geologists, paleontologists, and paleoanthropologists know this. Almost as important as the meaning is the utility.

    Nobody that I know who works in the period from the Middle Pleistocene to the present uses these terms when doing the actual research at a detailed level. We tend to use the glacial stages, mammalian stages, or other measures. Sure, you stick these terms on the chart for reference, but it isn’t that important.

  2. #2 John McKay
    February 1, 2008

    I would think the extinction of mammoths and their kin would make a pretty good marker for the post-Pleistocene period, whatever we call it. During the Pleistocene there were about twenty species of probiscideans, representing seven genera, spread across all the unglaciated parts of five continents. In a very short period of time mammoths, mastodons, and gomphotheres went extinct along with several dozen species of large mammals on four of those continents. Today, we have three species of probiscideans, representing two genera, spread across limited parts of two continents. The only places where this change isn’t very helpful is Australia and the refuges where elephants survive for the time being.

    Of course, since that extinction event is the beginning of a series of further anthropomorphic extinctions, litter, and spread of invasive species, I’m firmly on the side of the Anthropocene swallowing the Holocene. The we need to work on renaming the Pleistocene the Mammothocene.

  3. #3 Maria
    February 1, 2008

    Hmm. I must not have been very clear – I was trying to make the point that geologic time scale units are not actually obligated to do anything. If we wanted to divide history into even 100 million year chunks, and call them the Quintian, Sextian, Septian, etc… the boundaries wouldn’t correspond to anything interesting, but it would still be wrong to call that system “scientifically invalid”.

    By the definition of the Pleistocene that says it’s the period of time from 1.8 Ma to 11 ka (or whatever the equivalent is in marine isotopic stages), the Holocene is not part of the Pleistocene. And yes, if the majority of workers in the field and the International Commission on Stratigraphy told me that there was an epoch called the Jumpoffaclifficene, I would totally start talking about the Jumpoffaclifficene, too.

    Seismic hazard people sometimes use the Holocene, largely because it has been enshrined in the California code of regulations as the dividing line between “active fault” and “sure, go ahead, build wherever you want”. I’m sure that if that hadn’t been a pre-existing officially-recognized chunk of time, they would’ve picked another line… but they didn’t.

    I think in general the geologic time scale is losing its hegemony, though, not just among Late Quaternarists. I see people using glacial stages or the magnetic timescale or radiometric dates or references to local tectonic history or whatever else seems relevant. I’m all in favor of this – I can never remember the Cenozoic epochs anyway and it drives me batty when people don’t put absolute ages on their slides.

  4. #4 Laelaps
    February 1, 2008

    The term Anthropocene might eventually become useful, but I don’t think we’re there yet. If the Anthropocene is supposed to represent more large-scale effects from the Industrial Revolution to the present and on I think our effects on global ecology are better understood as an event rather than marking a boundary, at least as it stands now. Like you hint at in your post, though, we might not even be around by the time it becomes possible to make the determination, but I still think the Anthropocene is probably best left on the shelf for now.

  5. #5 Larry Ayers
    February 1, 2008

    Welcome to the ScienceBlogs clan, Maria!

  6. #6 andy
    February 1, 2008

    Welcome!

    What’s wrong with seismotectohydrogeology? Makes perfect sense to me.

  7. #7 Hob
    February 1, 2008

    “…uniquely anthropogenic fossil markers (beer bottle caps)…”

    That’s just the kind of typical Berkeley rock-hugger bias I’ve come to expect from this blog. The anthropogenic-beer-bottle-cap theory is just that: a theory! Many respected scientists believe that human activity is just one of many contributing factors. Clearly the subtext of your phrasing is that beer bottle caps are somehow not “natural” or not as good as other fossils, and that we should keep our beer in open bottles, or just drink wine like they do in California.

  8. #8 Caledonian
    February 1, 2008

    I was trying to make the point that geologic time scale units are not actually obligated to do anything.

    This is certainly true; however, isn’t there a tradition of making the distinctions begin and end at transition points within the geologic history?

    If that is the case, it’s not at all clear that the changes humans are making will exist for a sufficient period of time to call an ‘epoch’. A layer, possibly, or a boundary. But an epoch? If I recall correctly, we haven’t even been around for an age yet!

    BTW, welcome.

  9. #9 Maria Brumm
    February 1, 2008

    If we cause a mass extinction, it doesn’t really matter how long the climate and sedimentation changes persist. Cockroach geologists who are even remotely fossil-oriented will want to put a boundary at the change in species distribution.

  10. #10 BJN
    February 2, 2008

    We’ve already caused a mass extinction and its scale is increasing.

  11. #11 Gaynor
    February 2, 2008

    I’m tired of these cockroach geologists basing their geological boundaries on multicellular eukaryote distributions. When are they going to set up a *real* egalitarian system based on markers of bacterial/archaeal activity, eh?

  12. #12 Maria Brumm
    February 2, 2008

    Gaynor: Just as soon as the prokaryotes make some improvements to their taphonomy… also, geez, the cockroach geologists haven’t even evolved yet, give them some time!

  13. #13 Tim Eisele
    February 2, 2008

    The thing that’s been bugging me about this is, how much time should we allow for a transition between geological periods? I mean, given the level of accuracy of dating methods, and the actual amount of time it might take to switch from one state to another, can we really pin down the beginning of geological periods to as little as +/-5000 years? It seems to me that, if we assume that the effects of the human species last for at least a million years or so, the entire period that we call the “holocene” would vanish in the transition to the “anthropocene” if it were looked at from a vantage point of, say, 100 million years in the future.

  14. #14 Mr.Murder
    February 2, 2008

    Did the Tsunami event not start in the area BP runs what is essentially the world’s largest offshore drilling site?

    Do you have any data on the process of “fracturing” used to drill mudholes in oil wells and its potential geological impact?

    There may be another area worthy of comparison for such events, mapped across an occurrence plot. California in the mid to late 80′s and very early 90′s.

  15. #15 Jim D
    February 2, 2008

    As an interested lay person, I guess I’d like to see a more detailed assessment of what the long-term impacts of human civilization are going to be on the planet.

    I haven’t yet read The World Without Us, but I did see the History Channel documentary “Life After People.” Of course, it’s all speculation. But I think the question both the book and the show were exploring is relevant (“how long is our stuff going to persist”), at least if geologists are looking for a boundary event.

    Considering that both the book and show postulate that most of our stuff is going to crumble to dust in a few hundred years, I’m guessing that there really is a legitimate question as to whether or not our “future cockroach overlords” (FCOs) are going to find it all that significant.

    I guess a relevant factor — correct me if I’m wrong, but the further in the future our FCOs are, the more “noise” and less “signal” there will be for them.

  16. #16 Andrew Alden
    February 2, 2008

    I’m surprised to see the Holocene under attack. It may not be useful to Greg Laden, but it’s a very convenient shorthand for “today,” the world in which civilization arose and in which archaeologists operate. I thought the GSA Today paper, especially its Figure 1, made a good case for what the Holocene is–a particularly equable period of stable sea level, a cradle period. It doesn’t amount to beans to your prototypical hard-rock geologist, but it is dear to geomorphologists, environmental specialists and interdisciplinary sorts. To paraphrase Daniel Webster, it is, Sir, as I have said, a small epoch; but there are those who love it.

  17. #17 Chris Rowan
    February 3, 2008

    Personally, I have no trouble calling Marine Isotope Stage 1 the Holocene – where I do have a slight problem is with its current classification as an epoch distinct from the Pleistocene before it – a distinctiveness which is rather difficult to justify.

  18. #18 Andrew
    February 3, 2008

    While they’re adjusting the Pleistocene-Pliocene boundary (back to the base of the Gelasian age), maybe they can turn the Holocene from an epoch to an age too–put an end to it and demote it. It’s not like anyone in daily life makes a big deal about the rank of a time unit, we just use the name. Only occasionally does editorial correctness demand that you choose between, say, Cretaceous/Tertiary (Paleogene), Upper Cretaceous/Paleocene, and Maastrichtian/Danian.

  19. #19 Dave Godfrey
    February 3, 2008

    I don’t have a problem with keeping the Holocene as a separate epoch for historical reasons. If the proposal to split it up goes ahead then it should be abolished and fused with the rest of the Pleistocene.

    But the Anthropocene serves no useful purpose in my opinion. Lets divide things further! I propose the “Godfreyocene” which started in April 1979.)

    Where do they propose putting the golden spike? And if they use a numerical date when do they propose that the industrial revolution began? I’m not sure even historians agree on a date. Its fairly clear once you’re in it, but when do you mark it? Abraham Darby’s first furnace at Ironbridge perhaps?

  20. #20 Maria Brumm
    February 3, 2008

    As a hydrogeologist, I’d prefer to start the Anthropocene on July 16, 1945. It’s quite common to look at the tritium content of ground water as a rough measure of how old it is (or do tritium/helium-3 dates if we want a precise mesaure). But tritium has too short of a half-life to expect that the cockroach geologists will agree with me here.

    I’ll support the Godfreyocene if you don’t mind it being only 2 years long – the Brummocene starts in 1981 :)

    Tim and Jim, I’ll try to address some of your questions in my next real post.

  21. #21 hollowkatt
    February 4, 2008

    Finally someone who makes science funny.

    I for one welcome our Epoch-Defining Cockroach Overlords