Absolute dating numerical age geology
This is not circularity, it is the normal scientific process of refining one's understanding with new data. It happens in all sciences. If an inconsistent data point is found, geologists ask the question: However, this statistical likelihood is not assumed, it is tested , usually by using other methods e. Geologists search for an explanation of the inconsistency, and will not arbitrarily decide that, "because it conflicts, the data must be wrong.
If it is a small but significant inconsistency, it could indicate that the geological time scale requires a small revision. The continued revision of the time scale as a result of new data demonstrates that geologists are willing to question it and change it. The geological time scale is far from dogma. If the new data have a large inconsistency by "large" I mean orders of magnitude , it is far more likely to be a problem with the new data, but geologists are not satisfied until a specific geological explanation is found and tested.
An inconsistency often means something geologically interesting is happening, and there is always a tiny possibility that it could be the tip of a revolution in understanding about geological history. Admittedly, this latter possibility is VERY unlikely. There is almost zero chance that the broad understanding of geological history e. The amount of data supporting that interpretation is immense, is derived from many fields and methods not only radiometric dating , and a discovery would have to be found that invalidated practically all previous data in order for the interpretation to change greatly.
So far, I know of no valid theory that explains how this could occur, let alone evidence in support of such a theory, although there have been highly fallacious attempts e.
It contains a mixture of minerals from a volcanic eruption and detrital mineral grains eroded from other, older rocks. If the age of this unit were not so crucial to important associated hominid fossils, it probably would not have been dated at all because of the potential problems. After some initial and prolonged troubles over many years, the bed was eventually dated successfully by careful sample preparation that eliminated the detrital minerals.
Lubenow's work is fairly unique in characterising the normal scientific process of refining a difficult date as an arbitrary and inappropriate "game", and documenting the history of the process in some detail, as if such problems were typical. Another example is "John Woodmorappe's" paper on radiometric dating , which adopts a "compilation" approach, and gives only superficial treatment to the individual dates. Among other problems documented in an FAQ by Steven Schimmrich , many of Woodmorappe's examples neglect the geological complexities that are expected to cause problems for some radiometrically-dated samples.
This section is important because it places a limit on the youngest age for a specific ammonite shell -- Baculites reesidei -- which is used as a zonal fossil in western North America. It consistently occurs below the first occurrence of Bacultes jenseni and above the occurrence of Baculites cuneatus within the upper part of the Campanian, the second to last "stage" of the Cretaceous Period in the global geological time scale.
The biostratigraphic situation can be summarized as a vertically-stacked sequence of "zones" defined by the first appearance of each ammonite species: About 40 of these ammonite zones are used to subdivide the upper part of the Cretaceous Period in this area. Dinosaurs and many other types of fossils are also found in this interval, and in broad context it occurs shortly before the extinction of the dinosaurs, and the extinction of all ammonites.
The Bearpaw Formation is a marine unit that occurs over much of Alberta and Saskatchewan, and it continues into Montana and North Dakota in the United States, although it adopts a different name in the U. The numbers above are just summary values. Other examples yield similar results - i. The results are therefore highly consistent given the analytical uncertainties in any measurement. Eberth and Braman described the vertebrate paleontology and sedimentology of the Judith River Formation, a dinosaur-bearing unit that occurs stratigraphically below the Baculites reesidei zone the Judith River Formation is below the Bearpaw Formation.
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It should therefore be older than the results from Baadsgaard et al. An ash bed near the top of the Judith River Fm. Again, this is compatible with the age determined for the Baculites reesidei zone and its relative stratigraphic position, and even with the relative position of the two samples within the same formation.
How do these dates compare to the then current geological time scale? Here are the numbers they applied to the geological boundaries in this interval, compared to the numbers in the newer studies:. As you can see, the numbers in the rightmost column are basically compatible. Skeptics of radiometric dating procedures sometimes claim these techniques should not work reliably, or only infrequently, but clearly the results are similar: Most of the time, the technique works exceedingly well to a first approximation.
However, there are some smaller differences. The date for the Baculites reesidei zone is at least 0. Well, standard scientific procedure is to collect more data to test the possible explanations -- is it the time scale or the data that are incorrect? Obradovich has measured a large number of high-quality radiometric dates from the Cretaceous Period, and has revised the geological time scale for this interval. Specifically, he proposes an age of This is completely compatible with the data in Baadsgaard et al.
Skeptics of conventional geology might think scientists would expect, or at least prefer, every date to be perfectly consistent with the current geological time scale, but realistically, this is not how science works. The age of a particular sample, and a particular geological time scale, only represents the current understanding, and science is a process of refinement of that understanding.
In support of this pattern, there is an unmistakable trend of smaller and smaller revisions of the time scale as the dataset gets larger and more precise Harland et al. If something were seriously wrong with the current geologic time scale, one would expect inconsistencies to grow in number and severity, but they do not. The same trend can be observed for other time periods. Palmer and Harland et al.
The latter includes an excellent diagram summarizing comparisons between earlier time scales Harland et al. Since , there have been still more revisions by other authors, such as Obradovich for the Cretaceous Period, and Gradstein et al. As another example, Rogers et al. This is not uncommon. Besides the papers mentioned here, there are hundreds, if not thousands, of similar papers providing bracketing ranges for fossil occurrences.
The synthesis of work like this by thousands of international researchers over many decades is what defines geological time scales in the first place refer to Harland et al. Although geologists can and do legitimately quibble over the exact age of a particular fossil or formation e. The data do not support such an interpretation. The methods work too well most of the time.
Geologic Time Scale
In addition, evidence from other aspects of geology e. Prior to the availability of radiometric dating, and even prior to evolutionary theory, the Earth was estimated to be at least hundreds of millions of years old see above. Radiometric dating has simply made the estimates more precise, and extended it into rocks barren of fossils and other stratigraphic tools. The geological time scale and the techniques used to define it are not circular. They rely on the same scientific principles as are used to refine any scientific concept: There are innumerable independent tests that can identify and resolve inconsistencies in the data.
This makes the geological time scale no different from other aspects of scientific study. Refuting the conventional geological time scale is not an exercise in collecting examples of the worst samples possible. A critique of conventional geologic time scale should address the best and most consistent data available, and explain it with an alternative interpretation, because that is the data that actually matters to the current understanding of geologic time. Multimethod radiometric age for a bentonite near the top of the Baculites reesidei Zone of southwestern Saskatchewan Campanian-Maastrichtian stage boundary?
Canadian Journal of Earth Sciences, v. Stratigraphy, sedimentology, and vertebrate paleontology of the Judith River Formation Campanian near Muddy Lake, west-central Saskatchewan. Bulletin of Canadian Petroleum Geology, v. A Triassic, Jurassic and Cretaceous time scale. A Geologic Time Scale: A Geologic Time Scale, edition. Relative age inference in paleontology. A Creationist Assessment of Human Fossils. A Cretaceous time scale. Evolution of the Western Interior Basin. Geological Association of Canada, Special Paper 39, p. See archived copy instead.
Encyclopaedia Britannica 10, p. Creation Research Society Quarterly, v. This document discusses the way radiometric dating is used in geology rather than the details of how radiometric techniques work. It therefore assumes the reader has some familiarity with radiometric dating. For a technical introduction to the methods, I highly recommend these two books:. The Age of the Earth. Principles of Isotope Geology, 2nd.
John Wiley and Sons: An excellent source about the integration of radiometric dating, biostratigraphy the study of fossil succession and general stratigraphic principles is:. Principles of Stratigraphic Analysis. Growth of a Prehistoric Time Scale. A profusion of terms is applied to the different concepts, and, confusingly to the uninitiated, to the names applied to subdivisions of them e.