Uniformitarianism is the assumption 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. It has included the gradualistic concept that "the present is the key to the past" and is functioning at the same rates. Uniformitarianism has been a key principle of geology and virtually all fields of science...
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, 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.
By a metaphysical construct I mean any unproved or unprovable assumption that we all make and tend to take for granted. One example is the doctrine of uniformitarianism that asserts that the laws of nature ... have always been true in the past and will always be true in the future. It is the belief in that doctrine that permits scientists to demand repeatability in experiments. I like the word doctrine in this case because it makes clear that matters of faith are not restricted to creationists and that in the intellectual struggle for citizen enlightenment we need to be very clear just where the fundamental differences between science and theology lie. It is not, as many scientists would like to believe, in the absence of metaphysical underpinnings in science.
The principle of uniformity is not a law, not a rule established after comparison of facts, but a methodological principle, preceding the observation of facts ... It is the logical principle of parsimony of causes and of economy of scientific notions. By explaining past changes by analogy with present phenomena, a limit is set to conjecture, for there is only one way in which two things are equal, but there are an infinity of ways in which they could be supposed different.
The past history of our globe must be explained by what can be seen to be happening now. No powers are to be employed that are not natural to the globe, no action to be admitted except those of which we know the principle. ... But if the succession of worlds is established in the system of nature, it is in vain to look for any thing higher in the origin of the earth. The result, therefore, of our present enquiry is, that we find no vestige of a beginning,--no prospect of an end.
Lyell self-consciously aimed to present his brand of uniformitarianism as the scientific way of doing geology. But many of his opponents, including the so-called "catastrophists," were also reputable scientists: e.g., Cuvier, Whewell, Agassiz, Buckland, Sedgwick, Murchison. It is wrong to think that Lyell's critics were religious fundamentalists who believed that the earth was created in the very recent geological past, or that they relied on a Noachian deluge in their theories. ... Lyell was ... strongly committed to a steady-state, non-directional, non-progressive view of the earth.
One of the great advantages of his one-cycle theory of climate and life was that it could not be tested against any sort of evidence. ... Lyell's preoccupations led him to construct a theory of the earth out of distinctly fanciful speculations which were, of necessity, based upon no evidence at all. (Journal of the History of Biology, Vol. 10, No. 2, 1977, pp.317-339.)
Lyell relied heavily upon two bits of cunning to establish his uniformitarian views as the only true geology. First, he set up a straw man to demolish. ... The geologic record does seem to require catastrophes; rocks are fractured and contorted; whole faunas are wiped out. To circumvent this literal appearance, Lyell imposed his imagination upon the evidence. The geologic record, he argued, is extremely imperfect and we must interpolate into it what we can reasonably infer but cannot see. The catastrophists were the hard-nosed empiricists of their day, not the blinded theological apologists. Lyell's 'uniformity' is a hodgepodge of claims. One is a methodological statement that must be accepted by any scientist, catastrophist and uniformitarian alike. Other claims are substantive notions that have since been tested and abandoned. Lyell gave them a common name and pulled a consummate fast one: he tried to slip the substantive claim by with an argument that the methodological proposition had to be accepted... (Natural History, Vol. LXXX, No. 2, 1975.)
If you don't triumph over them, but compliment the liberality and candour of the present age, the bishops and enlightened saints will join us in despising both the ancient and modern physico-theologians. It is just the time to strike, so rejoice that, sinner as you are, the Q.R. is open to you. If I have said more than some will like, yet I give you my word that full half of my history and comments was cut out, and even as many facts; because I, or Stokes, or Broderip, felt that it was anticipating twenty or thirty years of the march of honest feeling to declare it undisguisedly. (Charles Lyell, K.M. Lyell, John Murray, London:1881. Vol.1, p.271.)
Catastrophism is the theory that the Earth has been affected in the past by sudden, short-lived, violent events, possibly worldwide in scope. ... Recently a more inclusive and integrated view of geologic events has developed, changing the scientific consensus [uniformitarianism] to accept some catastrophic events in the geologic past. This held that there have been violent and sudden natural catastrophes such as great floods and the rapid formation of major mountain chains.
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.
Paleoclimatology is the study of changes in climate taken on the scale of the entire history of Earth. ... Knowledge of precise climatic events decreases as the record goes further back in time.
Various mechanisms, involving changes in ocean circulation, changes in atmospheric concentrations of greenhouse gases or haze particles, and changes in snow and ice cover, have been invoked to explain these sudden regional and global transitions. ... All the evidence indicates that most long-term climate change occurs in sudden jumps rather than incremental changes.
There is still debate about the causes of all mass extinctions. In general, large extinctions may result when a biosphere under long-term stress undergoes a short-term shock.
The extinction of the dinosaurs was long thought to be a gradual process, but evidence collected since the late 1980s suggests it was abrupt, which is consistent with the idea that an asteroid impact caused it.
The Cretaceous–Paleogene (K–Pg) extinction event was a mass extinction of some three-quarters of plant and animal species on Earth, including all non-avian dinosaurs...
Geologist J Harlen Bretz conducted research and published many papers during the 1920s describing the Channeled Scablands. His theories of how they were formed required short but immense floods (500 cubic miles of water), for which Bretz had no explanation. Bretz's theories met with vehement opposition from geologists of the day, who tried to explain the features with uniformitarian theories. ... J.T. Pardee first suggested in 1925 to Bretz that the draining of a glacial lake could account for flows of the magnitude needed. Pardee continued his research over the next 30 years, collecting and analyzing evidence that eventually identified Lake Missoula as the source of the Missoula Floods and creator of the Channeled Scablands. ... Pardee's and Bretz's theories were accepted only after decades of painstaking work and fierce scientific debate. Research on open channel hydraulics in the 1970s put Bretz's theories on solid scientific ground. In 1979 Bretz received the highest medal of the Geological Society of America, the Penrose Medal, to recognize that he had developed one of the great ideas in the earth sciences.
After centuries of geological controversy it is now well established that the last major deglaciation of planet Earth involved huge fluxes of water from the wasting continental ice sheets, and that much of this water was delivered as floods of immense magnitude and relatively short duration.
Mount St. Helens
The observations at Mount St. Helens and elsewhere, however, show in miniature that adjustments toward the graded equilibrium condition can occur rapidly.