Saturday, June 28, 2008

The Principle of Uniformitariansim


The principle of uniformitarianism is one of the earliest formed principles of geology. It is a principle, not a theory.

The principle of uniformitarianism is stated simply as "the processes affecting Earth today are the same ones that affected it in the past" - as quoted from What Stories do Rocks Tell, at ClassZone. Besides describing the principle of uniformitarianism, the website goes on to outline the other principals of geology:

The principle of uniformitarianism is fundamental to understanding geology and working out what actually happened in the past, during the long history of the earth, during the eons of geologic time. This main principle is sometimes stated as "the present is the key to the past."

If geologists could not use what they see around them now, by studying geologic processes and relationships occurring and in place today, it would be difficult if not impossible to determine what had happened in the past. Any ideas, concepts, or hypotheses that a geologist might form about the past - anywhere or anywhen on earth - would be useless without the principle of uniformitarianism, simply because one could not go to the geologic record - which is also a record of events and processes that include the chemistry of the past, the physics of the past, the biology of the past, the hydrology of the past, the geochemistry of the past, the geophysics of the past, and the bio-geology of the past - and do any meaningful interpretation at all.

If, for example, sedimentary rock layers of the past were laid down sideways or vertical instead of in horizontal fashion as we see them being laid down today - say, because the gravity on earth worked very differently in the past - then any interpretation of what happened to older rock layers that are now folded, faulted, and otherwise deformed, would be incorrect. Another way of looking at this would be as described at MSN Encarta:

The principle of uniformitarianism depends on the 'uniformity of laws,' which assumes that the laws of physics and chemistry have remained constant. To test uniformity of laws, geologists can examine preserved one-billion-year-old ripples that look very much like ripples on the beach today. If gravity had changed, water and sand would have interacted differently in the past, and the ripple evidence would be different.

In other words, ripple marks today indicate that water has flowed or wind has blown1 (because we also see ripple marks created in areas of blowing sand), and therefore ripple marks in rock formations of the past also indicate the same thing. By measuring and comparing ripple marks formed today under different circumstances of water or wind formation, different speeds of water current or air movement, and different environments, a geologist can then apply the data collected today to the ripple marks of the past and hypothesize an environment in which those ancient ripple marks formed.

Geologists at first sometimes took the principle of uniformitarianism to such an extreme that catastrophic events of certain kinds were almost completely ruled out, perhaps because the principle was partly formulated as a tenet opposite to the then prevailing doctrine of catastrophism. The two major types of events somewhat ruled out by geologists of the past were huge, giant floods and huge, giant volcanic eruptions. The reason for these things being ruled out or overlooked while using the principle of uniformitariansim, is that these things - huge catastrophic floods, and huge catastrophic volcanic eruptions - are not seen happening on earth today. The discovery and recognition by J. Harlan Bretz of the very large series of floods that formed the Channeled Scablands of Washington state, eventually was accepted as something that 1) really happened and 2) could happen again if circumstances similar to those that caused the floods occurred again. It's interesting to note that it was in part the identification of huge ripple marks that clinched the acceptance of the way-larger-than-usual floods. In a way, then, the principle of uniformitarianism helped confirm Harlan Bretz's ideas - if you look at the size of ripples in rivers today and compare them to the size of the ripples formed by these past floods in the Channeled Scablands, you would have to conclude that an immense volume of water was required to form them.

Likewise, the recognition of the very large volcanic calderas of Tertiary age in central Nevada and of Quaternary age in Yellowstone Park, Wyoming made geologists realize that large, "catastrophic" volcanic eruptions are part of the earth's history and therefore could happen today/soon, or sometime in the near to far future. The relative size of the eruptions at Yellowstone (Yellowstone Park and environs actually contains several - at least three - calderas) compared to that of many volcanic eruptions that we, as people, think of as large or "catastrophic" is discussed at Yellowstone Caldera. It can be good to remember that events that are considered catastrophic are on the large end of a continuum of smaller to larger events, and that the large events are often considered catastrophic only because of the effect they could have on humans. We are the ones defining normal earth processes as catastrophic.

Anyone attempting to do geology without using the principle of uniformitarianism as described above, is really not doing geology at all.

1. I am reminded of the movie Little Big Man, in which Pawnee chief, Old Lodge Skins, says "...as long as grass grow, and wind blow, and the sky is blue." One of my favorite quotes, for some reason.

UPDATE 23Jun2010: Also see Rapid Canyon Formation and Uniformitarianism at Clastic Detritus and Of Catastrophic Floods and Canyons at 4.5 Billion Years of Wonder.

5 comments:

BrianR said...

Nice post ... if you haven't read it already, I recommend Stephen J. Gould's 1965 paper called "Is Uniformitarianism Necessary?" in which he breaks the principle into two concepts, one which is very old and not useful, and one which is what we mean when we speak about it today - that being the invariance of natural laws (which is part of science in general). You can get it here

It's a great essay. Psuedo- and anti-science types use the principle of uniformitarianism as one of their key "straw men" - they like to tear it down as if doing so somehow proves whatever they are pushing. Creationists do it with evolution and now, apparently, abiotic "enthusiasts" are attempting to apply it (not very well) for proving their odd and spectacularly inconsistent ideas.

Silver Fox said...

Thanks, Brian, for the compliment about the post, and for the link and reference. I felt inspired after certain recent discussions (could you guess?). Perhaps one needs a little uniformitarianism to be consistent! :D

Anonymous said...

This Uniformitarianism thing can explain certain events that happened in the past by referring to the events happened today. But the limitation of the same is that it cannot explain extinction events like that of the KT and the end-permian, well we don't have giant asteriods falling down every week...

But when come to reconstruct what happen during the Triassic cimmerian orogenic event, one can visit north India or the Himalayan region to get an idea of the real aftermath of an orogenic event as the cimmerian event happened about 200ma ago, there is hardly anything obvious left to be studied.

Silver Fox said...

What I wrote above in no way negated large-scale events such as giant, caldera-forming eruptions (sometimes colloquially called "supervolcanoes"). I wrote merely to explain the principle of uniformitarianism, not particularly to say that things that we see as catastrophic, or events that we see as unusual because they haven't happened within recorded history, didn't or can't happen. Those events, however, are largely studied in comparison to similar, smaller-scale events that have happened recently or are happening today.

Meteors hit the earth regularly; they are studied profusely partly so people can better understand what has happened in the past, and also to understand what might happen in the future.

We may have a large extinction in progress right now, according to some scientists. Only time will tell, of course. In this case, scientists are studying the past extinction events in order to understand the present.

I'll have to take your word on the latter, as I have not been to northern India or into the Himalayas. Hopefully some information can be found. It is kind of hard to study things for which no data exists!

Silver Fox said...

NOTE: I found Gould's Is Uniformitarianism Necessary? posted online.