Uniformitarianism, also known as theDoctrine of Uniformity or theUniformitarian Principle,[1] is the assumption that the same natural laws and processes that operate in our present-day scientific observations have always operated in the universe in the past and apply everywhere in the universe.[2][3] It refers toinvariance in themetaphysical principles underpinning science, such as the constancy ofcause and effect throughout space-time,[4] but has also been used to describe spatiotemporal invariance ofphysical laws.[5] Though an unprovablepostulate that cannot be verified using the scientific method,[6] some consider that uniformitarianism should be a requiredfirst principle in scientific research.[7]
Ingeology, uniformitarianism has included thegradualistic concept that "the present is the key to the past" and that geological events occur at the same rate now as they have always done, though many modern geologists no longer hold to a strict gradualism.[8] Coined byWilliam Whewell, uniformitarianism was originally proposed in contrast tocatastrophism[9] by Britishnaturalists in the late 18th century, starting with the work of thegeologistJames Hutton in his many books includingTheory of the Earth.[10] Hutton's work was later refined by scientistJohn Playfair and popularised by geologistCharles Lyell'sPrinciples of Geology in 1830.[11] Today, Earth's history is considered to have been a slow, gradual process, punctuated by occasional natural catastrophic events.
Abraham Gottlob Werner (1749–1817) proposedNeptunism, wherestrata represented deposits from shrinking seasprecipitated onto primordial rocks such asgranite. In 1785James Hutton proposed an opposing, self-maintaining infinite cycle based on natural history and not on theBiblical account.[12][13]
The solid parts of the present land appear in general, to have been composed of the productions of the sea, and of other materials similar to those now found upon the shores. Hence we find a reason to conclude:
- 1st, That the land on which we rest is not simple and original, but that it is a composition, and had been formed by the operation of second causes.
- 2nd, That before the present land was made, there had subsisted a world composed of sea and land, in which were tides and currents, with such operations at the bottom of the sea as now take place. And,
- Lastly, That while the present land was forming at the bottom of the ocean, the former land maintained plants and animals; at least the sea was then inhabited by animals, in a similar manner as it is at present.
Hence we are led to conclude, that the greater part of our land, if not the whole had been produced by operations natural to this globe; but that in order to make this land a permanent body, resisting the operations of the waters, two things had been required;
- 1st, The consolidation of masses formed by collections of loose or incoherent materials;
- 2ndly, The elevation of those consolidated masses from the bottom of the sea, the place where they were collected, to the stations in which they now remain above the level of the ocean.[14]
Hutton then sought evidence to support his idea that there must have been repeated cycles, each involvingdeposition on theseabed, uplift with tilting anderosion, and then moving undersea again for further layers to be deposited. AtGlen Tilt in theCairngorm mountains he found granite penetratingmetamorphicschists, in a way which indicated to him that the presumed primordial rock had beenmolten after the strata had formed.[15][16] He had read aboutangular unconformities as interpreted by Neptunists, and found anunconformity atJedburgh where layers ofgreywacke in the lower layers of the cliff face have been tilted almost vertically before being eroded to form a level plane, under horizontal layers ofOld Red Sandstone.[17] In the spring of 1788 he took a boat trip along theBerwickshire coast withJohn Playfair and the geologistSir James Hall, and found a dramatic unconformity showing the same sequence atSiccar Point.[18] Playfair later recalled that "the mind seemed to grow giddy by looking so far into the abyss of time",[19] and Hutton concluded a 1788 paper he presented at theRoyal Society of Edinburgh, later rewritten as a book, with the phrase "we find no vestige of a beginning, no prospect of an end".[20]
Both Playfair and Hall wrote their own books on the theory, and for decades robust debate continued between Hutton's supporters and the Neptunists.Georges Cuvier'spaleontological work in the 1790s, which established the reality ofextinction, 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 thebiblical flood.[21]
From 1830 to 1833Charles Lyell's multi-volumePrinciples 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,[22] 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 termsuniformitarianism for this idea, andcatastrophism for the opposing viewpoint, was coined byWilliam Whewell in a review of Lyell's book.Principles of Geology was the most influential geological work in the middle of the 19th century.
Geoscientists support diverse systems of Earth history, the nature of which rests on a certain mixture of views about the process, control, rate, and state which are preferred. Because geologists andgeomorphologists tend to adopt opposite views over process, rate, and state in the inorganic world, there are eight different systems of beliefs in the development of the terrestrial sphere.[23] All geoscientists stand by the principle of uniformity of law. Most, but not all, are directed by the principle of simplicity. All make definite assertions about the quality of rate and state in the inorganic realm.[24]
| Methodological assumption concerning kind of process | Substantive claim concerning state | Substantive claim Concerning rate | System of Inorganic Earth history | Promoters[25] |
|---|---|---|---|---|
| Same Kind of processes that exist today Actualism | Steady State Non-directionalism | Constant Rate Gradualism | Actualistic Non-directional Gradualism | Most of Hutton, Playfair, Lyell |
| Changing Rate Catastrophism | Actualistic Non-directional Catastrophism | Hall | ||
| Changing State Directionalism | Constant Rate Gradualism | Actualistic Directional Gradualism | Small part of Hutton, Cotta, Darwin | |
| Changing Rate Catastrophism | Actualistic Directional Catastrophism | Hooke, Steno, Lehmann, Pallas, de Saussure, Werner, and geognosists, Elis de Beaumont and followers | ||
| Different Kind of processes than exist today Non-Actualism | Steady State Non-directionalism | Constant Rate Gradualism | Non-Actualistic Non-directional Gradualism | Carpenter |
| Changing Rate Catastrophism | Non-Actualistic Non-directional Catastrophism | Bonnet, Cuvier | ||
| Changing State Directionalism | Constant Rate Gradualism | Non-Actualistic directional Gradualism | De Mallet, Buffon | |
| Changing Rate Catastrophism | Non-Actualistic Directional Catastrophism | Restoration cosmogonists, English diluvialists, Scriptural geologists |
Lyell's uniformitarianism is a family of four related propositions, not a single idea:[26]
None of these connotations requires another, and they are not all equally inferred by uniformitarians.[27]
Gould explained Lyell's propositions inTime's Arrow, Time's Cycle (1987), stating that Lyell conflated two different types of propositions: a pair ofmethodological assumptions with a pair ofsubstantive hypotheses. The four together make up Lyell's uniformitarianism.[28]
The two methodological assumptions below are accepted to be true by the majority of scientists and geologists. Gould claims 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 outcrop."[29]
The substantive hypotheses were controversial and, in some cases, accepted by few.[28] 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[29] that come before one can do science and so cannot be tested or falsified by science.
Stephen Jay Gould's first scientific paper, "Is uniformitarianism necessary?" (1965), reduced these four assumptions to two.[38] He dismissed the first principle, which asserted spatial and temporal invariance of natural laws, as no longer an issue of debate. He rejected the third (uniformity of rate) as an unjustified limitation on scientific inquiry, as it constrains past geologic rates and conditions to those of the present. So, Lyell's uniformitarianism was deemed unnecessary.
Uniformitarianism was proposed in contrast tocatastrophism, which states that the distant past "consisted of epochs of paroxysmal and catastrophic action interposed between periods of comparative tranquility"[39] 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 theChanneled Scablands due to the catastrophicMissoula 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.[40]Derek Ager has noted that "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."[41]
Modern geologists do not apply uniformitarianism in the same way as Lyell. They question if rates of processes were uniform through time and only those values measured during thehistory of geology are to be accepted.[42] The present may not be a long enough key to penetrating the deep lock of the past.[43] Geologic processes may have been active at different rates in the past that humans have not observed. "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."[44]
The current consensus is thatEarth's history is a slow, gradual process punctuated by occasional natural catastrophic events that have affected Earth and its inhabitants.[45] In practice it is reduced from Lyell's conflation, or blending, to simply the two philosophical assumptions. This is also known as the principle of geological actualism, which states that all past geological action was like all present geological action. The principle ofactualism is the cornerstone ofpaleoecology.[46]
Uniformitarianism has also been applied inhistorical linguistics, where it is considered a foundational principle of the field.[47][48] LinguistDonald Ringe gives the following definition:[47]
If language was normally acquired in the past in the same way as it is today – usually by native acquisition in early childhood – andif it was used in the same ways – to transmit information, to express solidarity with family, friends, and neighbors, to mark one's social position, etc. –then it must have had the samegeneral structure and organization in the past as it does today, and it must have changed in the same ways as it does today.
The principle is known in linguistics, afterWilliam Labov and associates, as theUniformitarian Principle or Unifomitarian Hypothesis.[49]
Asit is not in human record, but in natural history, that we are to look for the means of ascertaining what has already been, it is here proposed to examine the appearances of the earth, in order to be informed of operations which have been transacted in time past. It is thus that, from principles of natural philosophy,we may arrive at some knowledge of order and system in the economy of this globe, and mayform a rational opinion with regard to the course of nature, or to events which are in time to happen.
Hutton possessed an instinctive ability to reverse physical processes – to read landscapes backwards, as it were. Fingering the white quartz which seamed the grey granite boulders in a Scottish glen, for instance, he understood the confrontation that had once occurred between the two types of rock, and he perceived how, under fantastic pressure, the molten quartz had forced its way into the weaknesses in the mother granite.Review of Repcheck'sThe Man Who Found Time
Whilst visiting Allar's Mill on the Jed Water, Hutton was delighted to see horizontal bands of red sandstone lying 'unconformably' on top of near vertical and folded bands of rock.
It is ironic that Hutton, the man whose prose style is usually dismissed as unreadable, should have coined one of the most memorable, and indeed lyrical, sentences in all science: "(in geology) we find no vestige of a beginning,—no prospect of an end". In those simple words, Hutton framed a concept that no one had previously contemplated, that the rocks making up the earth today have not, after all, been here since Creation.
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.
