My (least) favorite geologic misconception

Modern geology is dictated by uniformitarianism as proposed by Charles Lyell in his Principles of Geology, a book that rightly displaced the "armchair speculations" of catastrophists.

In nearly any book about 19th century science, Charles Darwin, paleontology, or geology, the name Charles Lyell shows up at least once, even if only to state his connection with the idea of uniformitarianism. This important concept, often summarized as "the present is the key to the past," has often been described as triumphantly kicking catastrophist explanations out of geological science, researchers like Georges Cuiver and Louis Agassiz being denigrated in the literature for their association with more violent and abrupt changes in the earth's past. If uniformitarianism, as proposed by Lyell, is little more than "the present is the key to the past" there isn't much of a problem, but in truth Lyell's ideas about geology went far beyond this derived axiom. Likewise, while Cuvier and Agassiz favored a number of abrupt changes in the past, their views about the earth as a whole were not diametrically opposed from those of Lyell; catastrophism was distinct from uniformitarianism, but there was wide agreement between both groups as to a number of central ideas behind the emerging geological sciences.

Contrary to some of the statements made by Lyell and other proponents of uniformitarianism, catastrophists had no problem with using evidence gained from modern processes to explain much of geology. Instead, the main disparity between the two groups had to deal with a dynamic planet that experienced major ("catastrophic") changes in the past and one that was essentially balanced and in equilibrium with no addition of subtraction of modern geologic phenomena. Such concepts are among the "secrets" of geology that seemingly have to be learned over and over again by each new generation of geologists, especially since many books have supported something of a revisionist history of the discipline. Traditional narratives about the development of geology feature Lyell and Hutton as the cool-headed "good guys" while Cuvier and Agassiz are labeled as religiously-motivated zealots.

There are many facets to the hypotheses proposed by Lyell in the various edition of Principles of Geology, too many to detail here, but Lyell primarily saw the world in a balanced, "sensible" state. If there was a discontinuity or gap in the geologic record, it did not represent a quick change but rather signaled that another event occurred elsewhere to "balance out" the strata (i.e. if one area experienced uplift above the sea, another area was subsumed beneath the waves to keep the balance). All the forces and laws that formed the planet were still in action according to Lyell; none had been added, none were out of use, and the rates of change remained constant. When applied to paleontology such views gave rise to the satirical Prof. Ichthyosaurus, the earth seemingly cycling endlessly through phase after phase of finely-graded change. This is not the way we understand geology today, the rates of geologic change and modes of change varying widely temporally and spatially in the history of earth, yet what Stephen Jay Gould has called the "textbook cardboard" story continues to be promulgated. This is not to say that Lyell did not make important contributions to geology, but rather that we must understand what he said in context and stop paying lip-service to short blurbs parroted in textbook after textbook.

Nowhere is the current debate between uniformitarianism and catastrophism (two words that I feel create a false dichotomy, even if they are useful in pointing to extremes) as vicious as in the study of mass extinctions. While the disappearance of some groups of animals in past eras has been recognized for some time, a subdiscipline of geology concerned with such events has only recently emerged. Indeed, ever since the iridium layer was identified at the K/T boundary the debate about the impact of extraterrestrial bodies has been especially fierce. At this point it is abundantly clear than a large extraterrestrial body struck the earth in the area of the Yucatan peninsula 65 million years ago, but even when such data have been confirmed many scientists still debate how important this event was in the extinction of creatures that did not pass through into the Cenozoic.

Hypotheses for the extinction of the dinosaurs* are varied, from mammals with a taste for dinosaur eggs to voracious bugs to intense activity of the Deccan traps to the recession of the Western Interior Seaway to migratory populations bringing disease to new areas. Some of these may have played a factors, others were likely insignificant, but the specter of uniformitarianism vs. catastrophism still looms large. Are mass extinctions triggered by causes in action today writ large? Are they caused by unusual activity of earth-bound causes? Are they solely the result of extraterrestrial impacts? Are mass extinctions caused by a number of contingent factors unique to each period of the earth's history? As frustratingly vague as it may seem, the last question probably points us in the best direction, there being no common cause for the multiple mass extinctions of varying intensity during the history of the planet. Still, there have been seemingly odd marriages of catastrophism and uniformitarianism in recent years, the emergence of meteor-impact as a tenable extinction mechanism being married to a 26 million year periodicity of extinction in the "Nemesis" hypothesis. Even as I was preparing this piece I became aware of a paper just published in the new journal Nature Geoscience which postulates the the rise of biodiversity in the Ordovician resulted from asteroid impacts opening up new niches to survivors, extinction and evolution being closely linked to each other. Whether this hypothesis stands or falls will require further study and a greater amount of supporting evidence, but it at least reflects that we have entered a time of transition where the caricatured versions of uniformitarianism and catastrophism no longer constrain geological science.

*While other groups of animals became extinct at the end of the Cretaceous, it is the dinosaurs that have framed much of the debate. This doesn't do justice to the magnitude of the extinction, but at the moment it seems to represent where most of the attention is paid.

I find it difficult to keep throwing around the terms uniformitarianism and catastrophism, however. They can be useful markers, but "useful" is not the same as "accurate," and the words carry so much baggage that they more often conflate debates rather than solve them. I doubt that modern paleontologists are thinking in terms of adhering to a catastrophist or uniformitarian program; modern geology does not fit into either category, and the meanings of the terms today are generally watered down versions of what they meant when originally proposed and debated. Take the words of Clarence King, for example, delivered in an address to the Sheffield Science School at Yale in 1877;

Men are born either catastrophists or uniformitarians. You may divide the race into imaginative people who believe in all sorts of impending crises, -physical, social, political, -and others who anchor their very souls in statu quo. There are men who build arks straight through their natural lives, ready for the first sprinkle, and there are others who do not watch Old Probabilities or even own an umbrella. This fundamental differentiation expresses itself in geology by means of the two historic sects of catastrophists and uniformitarians. Catastrophism, I doubt not, was the only school among the Pliocene Californians after their families and the familiar fauna and flora of their environment had been swept out of existence by basalts and floods.

For King, catastrophism was a truer science because it reflected something visceral about the human experience, namely times of upheaval and chaos experienced by earlier groups of people and passed down to succeeding generations. Much like Lyell originally extended his geologic hypotheses to biology, so too does King dismiss evolution by a "Malthusian struggle," the ultimate explanation for the forms of life being attributable to a creator. It is no secret that Lyell's Principles of Geology had a profound impact on Charles Darwin during his time aboard the Beagle and beyond, such a connection likely raising the ire of those who thought like King, and similar parallels between geologic uniformitarianism and catrastrophism can be seen today in debate about evolutionary mechanisms. This is the classic "adaptationist" argument, although it too seems to suffer from some amount of mischaracterization and hyperbole. Again, this is a topic that I don't think I can fully do justice to here, but the main areas of contention have generally centered around the relative importance of natural selection, the presence of other evolutionary mechanisms, levels of selection, and the rate of evolution.

The state of the adaptationist debate was perhaps most famously summed up in the "spandrels" paper of Gould and Lewontin, the two scientists proposing that it is absurd to regard every trait out of context from an organism (and even evolutionary history) in an attempt to discover what it is "for." Such exercises might provide a starting point or a springboard, but they lead down too many blind alleys and post hoc explanations to be taken at face value. To put it another way, we should be careful in saying that a particular structure takes a certain form because it was adapted for that purpose, especially because (as Greg Laden has noted) a certain trait can be an adaptation or exaptation depending on what context it is being placed in. To speak of the diminutive arms of Tyrannosaurus rex being adapted "for" a particular purpose (to borrow an example from Gould and Lewontin's paper) out of context from the rest of the individual animal and the evolutionary history of the species is too oversimplified to provide an answer to why this particular species had such small arms, although testing the hypotheses developed by such an approach can give scientists further clues to consider. If we were to simply be content with considering what this or that trait is for, though, we would soon run into trouble when the structure or behavior we tried to explain did not have a modern analog to work backwards from; sometimes the present lacks the keys to the past.

In the end, the idea that "the present is the key to the past" can provide geologists from a good starting point, but it is not an iron-clad rule that must be adhered to. As V.R. Baker once wrote;

Geology is a realistic science, not an actualistic one. A science that would limit itself to using the present as the arbitrator of what counts as natural evidence condemns itself to being actualistically unrealistic.

It is difficult, then, to buy into the story written by the "winning" side of the uniformitarianism/catastrophism debate, and although many do not go out of their way to understand this from the original texts it has become more ingrained in the study of geology. Geologists turn to the rocks themselves for clues as to what might have occurred, and in areas that have previously been dogged by a firm reliance on modern analogs (like paleoclimatology), there seems to be an increasing understanding that the exceptions to the uniformitarian rules need to be more fully understood. Just as evolutionary science has changed since Darwin wrote On the Origin of Species by Natural Selection, we still recognize his central role in making evolution a scientifically tenable idea. Likewise, geology has moved far beyond what Lyell proposed in Principles of Geology, but we can still recognize his contributions without feeling compelled to adhere to aspects of his work that are no longer tenable.

References;

Baker, V.R. (1998) "Catastrophism and uniformitarianism: logical roots and current relevance in geology." Geological Society, London, Special Publications Vol. 143, pp. 171-182;

Gould, S.J.; Lewontin, R.C. (1979) "The Spandrels of San Marco and the Panglossian Paradigm: A Critique of the Adaptationist Programme." Proceedings of the Royal Society of London. Series B, Biological Sciences, Vol. 205 (1161), pp. 581-598

King, C. (1877) "Catastrophism and Evolution." The American Naturalist Vol. 11 (8), pp. 449-470.

Raup, D.M.; Sepkoski, Jr., J.J. (1984) "Periodicity of extinctions in the geologic past." Proceedings of the National Academy of Sciences, Vol. 81, pp. 801-805

Schmitz, B.; Harper, D.A.T.; Peucker-Ehrenbrink, B.; Stouge, S.; Alwmark, C.; Cronholm, A.; Bergström, S.M.; Tassinari, M.; Xiaofeng, W. (2008) "Asteroid breakup linked to the Great Ordovician Biodiversification Event." Nature Geoscience Vol. 1, pp. 49 - 53

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Thank you for writing this; I'll be forwarding it around.

Nicely done.

For those who might want further information on this, Gould has a good discussion in his Time's Arrow, Time's Cycle about the cardboard history of the catastrophism/uniformitarianism debate, as well as the multiple meanings Lyell gave to his version of uniformitarianism.

Whewell and Lyell both muddied the waters by repeatedly blurring the distinction between uniformity of rate, state and cause. What's interesting is that while we pay acres of lip-service to Lyell, much of modern geology is obsessed with what Whewell would have called "palaetiology" i.e. revealing the hidden narratives of the earth. I think this would surprise old prof. Ichthyosaur whose general take on Earth history was essentially: "same schist different day."

Sorry, that was terrible.

In my old age I've outgrown my loathing of simplistic dichotomies. Sure, they belittle the multidimensional subtlety, but they can also be great heuristic tools. And sooner or later they generally weather away anyway--when was the last time you saw a Neptunist and a Plutonist going at it in ye olde public square?

It's especially interesting that you bring up Schmitz et al., Brian, since your paper reviewing the applicability of neoecological concepts to patterns of macroextinction and macroevolution is overdue!

Nice post Brian. It seems to me that the catastrophism/uniformitarism debate has evolved into an argument over which is has been more important factor in the geological evolution of the planet - the pervasive but slow processes such as erosion and tectonic drift, or the intermittent but more spectacular events such as asteroid impacts and flood basalts. Of course, if you actually start looking at things over the appropriate - geological - timescales, the distinction possibly becomes a bit blurry.

I picked up a copy of Lyell over Christmas for exactly the purpose of exploring this debate in more detail. It will probably be a while before I have anything sensible to say, though...

Good post and interesting topic.

Make sure to read Gould's essay from 1965 called "Is uniformitarianism necessary?" from the American Journal of Science, Vol. 263, March 1965, p. 223-228.

Here's the abstract...short and directly to the point:

"Uniformitarianism is a dual concept postulating uniformity of rates of geologic change and time and space invariance of natural laws. The first is false and inhibits hypothesis formation, the second belongs to science as a whole and is not unique to geology. The first concept, titled substantive uniformitarianism, is incorrect and should be abandoned; the second, titled methodological uniformitarianism, is now superfluous and is best confined to the past history of geology."

The way Gould separates the concept into (1) substantive uniformitarianism and (2) methodological uniformitarianism clears up a lot of the mud regarding this topic.

Here's another quote from Gould:

"We can extrapolate observed rates or conditions to past times (leading to substantive uniformitarianism) or because we establish our natural laws by observing present processes and then extrapolate the laws (leading to methodological uniformitarianism). Both postulate uniformity, but, according to whether this be a uniformity of rates of the material processes themselves or of the abstracted laws by which they operate, two distinct concepts arise."

It's a good read...I haven't read it since an advanced stratigraphy class I took...but, I might pull it out again after your post.

I had no idea the debate was so lively, or that anyone would believe that a person is either born an uniformitarist or catastrophist.

The important part of uniformitarism is that it spelled out the idea that geological processes work the same way they always have, ie: plate tectonics, mountain building, river formation, deposition, etc. I would argue that an extra terrestrial impact is not a geological process, but an event. I know there are some hyper-uniformitarists who believe(d) that what looked like impact craters on the Earth's surface were actually the result of normal volcanic processes (this was applied to Meteor Crater in Arizona for a long time, despite the name).

As for catastrophism, it was important to remove the religious aspect from geology. We should not attribute the extinction of a large group of animals to a flood and then announce that it must be Noah's flood. But the idea of catastrophism is certainly alive and well in the geomorphology I was taught. Until geologically recently, the province in which I grew up was covered by the Laurentide and Cordilleran Ice Sheets. When the Laurentide Ice Sheet began to retreat, it created large pro-glacial lakes that were hemmed in by ice. When the ice retreated far enough for the water to find an outlet, it created catastrophic meltwater channels (that's what they're really called, too), which are the ancestors of today's modern river valleys. Almost every river valley in Alberta was formed this way, and it's estimated that it look days to months to carve these channels - very quickly compared to normal river valley formation.

The East African Rift Valley is also showing some examples of catastrophism. In 2006 (I think?) a large fissure opened up within the space of a few days. If I remember right, it was 80km long. But these sorts of examples shouldn't overshadow the normal, slower geological processes that shape the Earth's surface.

As for the mass extinctions, I've always thought it was weird when people try to look for one cause. Each time it involved different taxa in different environments and the amount of taxa that went extinct varies greatly. Why should one thing always be responsible for this?

Well said Melanie.

When one appreciates deep time they realize how common large-magnitude/episodic events (catastrophes?) are. In fact, the occurrence of such events at long time scales (>10^6 yrs) is inevitable. There's a great paper by Gretener (1969) called "The significance of the rare event in geology" where he goes through a bunch of probabilistic scenarios showing how frequent (and inevitable) such large-magnitude/episodic events (catastrophes) are.

Over the course of my own training and research I've sort of melded this dichotomy together. That is, the significance of these events is everywhere in the geologic record. The evidence is everywhere! Meaning...how can we call these catastrophes when they happen all the time? Which is why I, personally, do not like the phrase "the present is the key to past". Attached to this is a view that the snapshot-in-time that is the present is representative. Not so much in conditions or processes, but in a temporal sense.

Rather, I view the occurrence of catastrophes within the context of uniformitarianism. Catastrophes are just another process in that sense. The problem, as always, comes back to our ridiculously short duration relative to Earth history introducing the temporal bias.

I'm kinda rambling...hope that gets across.

Rather, I view the occurrence of catastrophes within the context of uniformitarianism. Catastrophes are just another process in that sense. The problem, as always, comes back to our ridiculously short duration relative to Earth history introducing the temporal bias.

That's my take too: what happens on this planet is the sum of many different processes, and whilst the nature of the processes themselves has not changed much over time, their relative contributions, rates, and hence their geological expression, have.

I have to say that Gould's piece has always rubbed me up the wrong way slightly - to a certain extent I feel he set up a false dichotomy just so he could take potshots at biologists who didn't agree with him about punctuated equilibrium.