|Distant spiral galaxy NGC4603 [Courtesy NASA]||Ceiling of central rotunda, National Museum of Art of Catalunya|
The term "uniformitarianism" actually arose in the 19th century, when Charles Lyell published his multi-volume treatise Principles of Geology. The subtitle of this work was "An attempt to explain the former changes of the Earth's surface by reference to causes now in operation." The terms "uniformitarianism" and "catastrophism" were actually coined by William Whewell in a review of Lyell's book.
However, modern geology and biology have long since moved beyond these simple concepts, recognizing that while the earth's history is a slow process of gradual change, this process has been punctuated by periodic natural catastrophic events. For example, in the late twentieth century, J. Harlan Bretz demonstrated that the Scablands in eastern Washington state were formed from a large flood, which in turn resulted when a glacial lake broke through an ice dam. Similarly, in 1980, Luis Alvarez proposed that an asteroid impact was responsible for the extinction of dinosaurs 65 million years ago. Modern scientists are more apt to use the term "actualism" to refer to this combination of slow processes and catastrophic events [Isaak2007, pg. 161].
In articles on geologic ages (see Ages) we presented a chart with the various geologic eras and their ages. In the articles on radiometric dating (see Radiometric dating) and radiocarbon dating (see Radiocarbon dating), we briefly described how these dates are calculated using radiometric dating techniques. As we pointed out in those articles, these ages are based on known rates of radioactivity, a phenomenon that is rooted in fundamental laws of physics and follows simple mathematical formulas. In a related article on the reliability of radiometric dating (see Reliability), we discussed in detail how these methods have been tested and refined over the years, and why they deserve the trust that scientists place in them.
As another item of evidence, researchers studying a natural nuclear reactor in Africa have concluded that the fine structure constant ("alpha"), which is a key parameter in analysis of radioactive decay, has not changed measurably in hundreds of millions of years [Barrow2007, pg. 124-128].
Perhaps the most dramatic confirmation that the constants of physics have not changed significantly over cosmic time was announced in March 2016. Researchers in the Netherlands and Australia announced that by careful analysis of astronomical spectra in a galaxies up to 12.4 billion light-years away (which means that the reactions they studied occurred 12.4 billion years ago), they were able to conclude that the proton-to-electron mass ratio (approximately 1836.1526) has not changed by more than 0.0005 percent from its present value over this period of time [Srinivasan2016].
Thus scientists are on very solid ground in asserting that rates of radioactivity have been constant over geologic time, and that the consensus dates of the geologic ages are reliable.
In addition to the references mentioned above, useful information is available in online articles by Roger Wiens [Wiens2002] and Brent Dalrymple [Dalrymple2006]. For additional discussion, see