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Uniformitarianism, in the philosophy of science, assumes that the same natural laws and processes that operate in the universe now, have always operated in the universe in the past and apply everywhere in the universe. Its methodology is frequently summarized as "the present is the key to the past," because it holds that all things continue as they were from the beginning of the world.

The concept of uniformity in geological processes can be traced back to the Persian geologist, Avicenna (Ibn Sina), in The Book of Healing, published in 1027. Modern uniformitarianism was formulated by Scottish naturalists in the late 18th century, starting with the work of the geologist, James Hutton, which was refined by John Playfair and popularised by Charles Lyell's Principles of Geology in 1830. The term uniformitarianism was coined by William Whewell, who also coined the term catastrophism for the idea that the Earth was shaped by a series of sudden, short-lived, violent events.

History of Uniformitarianism

The concept of uniformitarianism in geology was first proposed in the 11th century by the Persian geologist, Avicenna (Ibn Sina, 980-1037), who provided the first uniformitarian explanations for geological processes in The Book of Healing (1027). He observed that mountains were formed after a long sequence of events that predate human existence. While discussing the formation of mountains, he explained:

Later in the 11th century, the Chinese naturalist, Shen Kuo, also recognized the concept of 'deep time'. After The Book of Healing was translated into Latin in the 12th century, a few other scientists also reasoned in uniformitarian terms.

18th century

The earlier conceptions likely had little influence on 18th century European geological explanations for the formation of the Earth. Abraham Gottlob Werner proposed Neptunism where strata were deposits from shrinking seas precipitated onto primordial rocks such as granite. An opposing idea was set out in 1785 by James Hutton, who proposed a self-maintaining infinite cycle.

Hutton then sought evidence to support his idea that there must have been repeated cycles, each involving deposition on the seabed, uplift with tilting and erosion then undersea again for further layers to be deposited. At Glen Tiltmarker in the Cairngorm mountainsmarker he found granite penetrating metamorphic schists, in a way which indicated to him that the presumed primordial rock had been molten after the strata had formed. He had read about angular unconformities as interpreted by Neptunists, and found Hutton's Unconformity at Jedburghmarker where layers of greywacke in the lower layers of the cliff face have been tilted almost vertically before being eroded to form a level plane, under horizontal layers of Old Red Sandstone. In the Spring of 1788 he took a boat trip along the Berwickshiremarker coast with John Playfair and the geologist Sir James Hall, and found a dramatic unconformity showing the same sequence at Siccar Pointmarker. Playfair later recalled that "the mind seemed to grow giddy by looking so far into the abyss of time", and Hutton concluded a 1788 paper he presented at the Royal Society of Edinburgh, later rewritten as a book, with the phrase "we find no vestige of a beginning, no prospect of an end."

Both Playfair and Hall wrote their own books on the theory, and for decades there was a robust debate between Hutton's supporters and the Neptunists. Georges Cuvier's paleontological work in the 1790s, which established the reality of extinction, explained this by local catastrophes, after which other fixed species repopulated the affected areas. In Britain, geologists adapted this idea into "diluvial theory" which proposed repeated worldwide annihilation and creation of new fixed species adapted to a changed environment, initially identifying the most recent catastrophe as the biblical flood.

19th century

From 1830 to 1833 Charles Lyell's multi-volume Principles of Geology was published. The work's subtitle was "An attempt to explain the former changes of the Earth's surface by reference to causes now in operation". He drew his explanations from field studies conducted directly before he went to work on the founding geology text, and developed Hutton's idea that the earth was shaped entirely by slow-moving forces still in operation today, acting over a very long period of time. The terms uniformitarianism for this idea, and catastrophism for the opposing viewpoint, were coined by William Whewell in a review of Lyell's book. Principles of Geology was the most influential geological work in the middle of the 19th century, and did much to put geology on a modern footing.

Lyell's uniformitarianism

According to Reijer Hooykaas (1963), Lyell's uniformitarianism is a family of four related propositions, not a single idea:
  • Uniformity of law – the laws of nature are constant.
  • Uniformity of methodology – the appropriate hypotheses for explaining the geological past are those with analogy today.
  • Uniformity of kind – past and present causes are all of the same kind, have the same energy, and produce the same effects.
  • Uniformity of degree – geological circumstances have not changed over time.

None of these connotations requires another, and they are not all equally inferred by uniformitarians.

Stephen Jay Gould's first scientific paper, Is uniformitarianism necessary? (1965), reduced these four interpretations to two, methodological and substantive uniformitarianism. He dismissed the first principle, which asserted spatial and temporal invariance of natural laws, as no longer an issue of debate. He rejected the second as an unjustified limitation on scientific inquiry, as it constrains past geologic rates and conditions to those of the present. Later, Gould expanded on these related propositions in Time's Arrow, Time's Cycle (1987), stating that Lyell conflated two different types of propositions: a pair of methodological assumptions with a pair of substantive hypotheses.

Methodological assumptions
The methodological assumptions are universally acclaimed by scientists, and embraced by all geologists. Gould further states that these philosophical propositions must be assumed before you can proceed as a scientist doing science. "You cannot go to a rocky outcrop and observe either the constancy of nature's laws or the working of unknown processes. It works the other way around." You first assume these propositions and "then you go to the out crop of rock."

  • Uniformity of law: Natural laws are constant across space and time.

The axiom of uniformity of law is necessary in order for scientists to extrapolate inductive inference into the unobservable past. As James Hutton wrote: “If the stone, for example, which fell today, were to rise again tomorrow, there would be an end of natural philosophy [i.e. science], our principles would fail, and we would no longer investigate the rules of nature from our observations.” In essence, the constancy of natural laws must be assumed in our study of the past, because if we do not, then we cannot meaningfully study the past. Making inferences about the past is wrapped up in the difference between studying the observable present and the unobservable past. In the observable present, induction can be regarded as self-corrective. That is to say, our erroneous beliefs about the observable world can be proven wrong and corrected by other observations. This is Popper's principle of falsifiability. However, past processes are not observable by their very nature. Therefore, in order to come to conclusions about the past, we must assume the invariance of nature's laws.

  • Uniformity of process: If a past phenomenon can be understood as the result of a process now acting in time and space, do not invent an extinct or unknown cause as its explanation.

“We should try to explain the past by causes now in operation without inventing extra, fancy, or unknown causes, however plausible in logic, if available processes suffice.” This is known as the scientific principle of parsimony or Occam's razor.

Substantive hypotheses
The substantive hypotheses were controversial and, in some cases, accepted by few. These hypotheses are judged true or false on empirical grounds through scientific observation and repeated experimental data. This is in contrast with the previous two philosophical assumptions that come before one can do science and so cannot be tested or falsified by science.

  • Uniformity of rate: Change is typically slow, steady, and gradual.

Gould explained that according to uniformity of rate mountain ranges or grand canyons are built by accumulation of near insensible changes added up through vast time. Some major events such as floods, earthquakes, and eruptions, do occur. But these catastrophes are strictly local. They neither occurred in the past, nor shall happen in the future, at any greater frequency or extent than they display at present. In particular, the whole earth is never convulsed at once.

  • Uniformity of state: Change is evenly distributed throughout space and time.

The uniformity of state hypothesis (i.e. steady-stateism) implies that throughout the history of our earth there is no progress in any inexorable direction. The planet has almost always looked and behaved as it does now. Change is continuous, but leads nowhere. The earth is in balance: a dynamic steady state.

20th Century

Uniformitarianism is a basic principle of modern geology. It was originally proposed in contrast to catastrophism, which states that the distant past "consisted of epochs of paroxysmal and catastrophic action interposed between periods of comparative tranquility" Especially in the late 19th and early 20th centuries, most geologists took this interpretation to mean that catastrophic events are not important in geologic time; one example of this is the debate of the formation of the Channeled Scablandsmarker due to the catastrophic Missoula glacial outburst floods. An important result of this debate and others was the re-clarification that, while the same principles operate in geologic time, catastrophic events that are infrequent on human time-scales can have important consequences in geologic history.
“Geologists do not deny uniformitarianism in its true sense, that is to say, of interpreting the past by means of the processes that are seen going on at the present day, so long as we remember that the periodic catastrophe is one of those processes.
Those periodic catastrophes make more showing in the stratigraphical record than we have hitherto assumed.”
Even Charles Lyell thought that ordinary geological processes would cause Niagara Fallsmarker to move upstream to Lake Eriemarker within 10,000 years, leading to catastrophic flooding of a large part of North America.

Unlike Lyell, modern geologists do not apply uniformitarianism in the same way. They question if rates of processes were uniform through time and only those values measured during the history of geology are to be accepted. The present may not be a long enough key to penetrate the deep lock of the past. Geologic processes may have been active at different rates in the past that humans have not witnessed. “By force of popularity, uniformity of rate has persisted to our present day. For more than a century, Lyell’s rhetoric conflating axiom with hypotheses has descended in unmodified form. Many geologists have been stifled by the belief that proper methodology includes an a priori commitment to gradual change, and by a preference for explaining large-scale phenomena as the concatenation of innumerable tiny changes.”

Thus the current scientific consensus is that Earth's history is a slow, gradual process punctuated by occasional natural catastrophic events that have affected Earth and its inhabitants. In practice it is reduced from Lyell's conflation to simply the two philosophical assumptions. This is also known as the principle of actualism , which states that all past geological action was like all present geological action. The principle of actualism is the cornerstone of paleoecology.

See also


  1. Uniformitarianism: World of Earth Science
  2. Concept of Uniformitarianism
  3. Stephen Toulmin and June Goodfield (1965), The Ancestry of Science: The Discovery of Time, p. 64, University of Chicago Press (cf. The Contribution of Ibn Sina to the development of Earth sciences)
  4. Scottish Geology - Glen Tilt
  5. Hutton's Unconformity
  6. Wilson, Leonard G. "Charles Lyell" Dictionary of Scientific Biography. Ed. Charles Coulston Gillispie. Vol. VIII. Pennsylvania, Charles Scribner's Sons, 1973
  7. Reijer Hooykaas, Natural Law and Divine Miracle: The Principle of Uniformity in Geology, Biology, and Theology, Leiden: EJ Brill, 1963.
  8. David Cahan, 2003, From Natural Philosophy to the Sciences, p 95 ISBN 9780226089287.
  9. Gould, S. J. 1965. Is uniformitarianism necessary? American Journal of Science 263: pp. 223–228.
  10. William J. Whewell, Principles of Geology, Charles Leyell, vol. II, London, 1832: Quart. Rev., v. 47, p. 103-123.
  11. Allen, E. A., et. al, 1986, Cataclysms on the Columbia, Timber Press, Portland, OR. * "Bretz knew that the very idea of catastrophic flooding would threaten and anger the geological community. And here's why: among geologists in the 1920's, catastrophic explanations for geological events (other than volcanos or earthquakes) were considered wrong minded to the point of heresy." p. 42. * "Consider, then, what Bretz was up against. The very word 'Catastrophism' was heinous in the ears of geologists. ... It was a step backwards, a betrayal of all that geological science had fought to gain. It was heresy of the worst order." p. 44 * "It was inevitable that sooner or later the gological community would rise up and attempt to defeat Bretz's 'outrageous hypothesis.'" p 49 * "Nearly 50 years had passed since Bretz first proposed the idea of catastorphic flooding, and now in 1971 his arguments had become a standard of geological thinking." p. 71
  12. The Columbia Encyclopedia Sixth Edition, uniformitarianism © 2007 Columbia University Press.


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