Excerpt from Paul LaViolette's 1983 Ph.D. dissertation
"Galactic Explosions, Cosmic Dust Invasions, and Climatic Change"
. . .In the remainder of this section it will be argued that the majority of the extinctions actually took place in a short space of time about 12,000 C-14 years BP (~14,000 calendar years B.P.),* and that the apparent temporal dispersion of the dates may be due to a number of causes. For example, excessively old dates may be due to contamination of the remains with old carbon or to the alluvial reworking of older fossils from preexisting deposits. Excessively young dates may be due to contamination with young carbon or may reflect an unusually high C-14 content in the remains associated with a brief episode of intense cosmic ray bombardment. Martin (1967), for example, argues that many radiocarbon dates assigned to the remains of Pleistocene megafauna should not be trusted. He cites the problematically young date of 2,040±90 C-14 years BP found for the terminal Pleistocene deposits in St. Petersburg, Florida and also questions the youth of several mastodon remains found in Michigan and dated at around 6000 C-14 years BP. Because of these few dates, which are in obvious error, he warns that all C-14 dates of mastodon remains may be in error to some degree. He states (p. 98):
Is it possible that all postglacial dates on mastodons are overshots? No skeptical archaeologist would consider accepting a radiocarbon date of 6,000 to 8,000 years on an alleged Clovis site before subjecting it to the most minute excavation and examination, without demanding an effort at replication of the date on the critical beds, without considering carefully all the possibilities of intrusion, and without a field demonstration of the evidence to equally critical colleagues.
Variability in radiocarbon dates is also encountered in remains unearthed from the permafrost muck layer in Alaska and Siberia. In Alaska, dates on remains from essentially the same muck layer have been found to range from less than 200 C-14 years BP for mammoth-bearing deposits from Sullivan Creek (Martin, 1967, p. 93) to greater than 30,000 C-14 years BP for similar deposits near Fairbanks (Broecker, Kulp, and Tucek, 1956). In Siberia, dates on wood and animal remains from the mammoth horizon have ranged from 11,500 C-14 years BP (Taimyr Peninsula) to 30,000 C-14 years BP (Lena River); see Martin (1967). However, it would be incorrect to interpret this wide range of dates as being indicative of the span of time during which this silt layer was being deposited. As was pointed out in Section 10.2, there is substantial evidence to indicate that the mammoth horizon in Northern Siberia and the Late Wisconsin Goldstream Formation in Alaska were deposited in a short space of time by a flood (or by floods) of water.
Usually young radiocarbon dates may be accounted for within the context of the Galactic Explosion Hypothesis [dissertation's hypothesis]. For example, in Chapter 7, Section 7.2 (p. 392) it is suggested that a period of unusually intense solar flare activity (or a T Tauri-like solar outburst) may have been involved in simultaneously producing the Gothenburg-Erieau-Laschamp (G/E/L) geomagnetic excursion and in clearing out dust from the inner portion of the Solar System; also recall Figure 4.5 (Chapter 4, p. 277). If so, such an event could temporarily have produced very high solar cosmic ray intensities which in turn would have produced abnormally high levels of C-14 in the atmosphere. Also, excess C-14 may also have been produced within the animal remains through the capture of secondary neutrons by nitrogen nuclei present in protein tissue such as collagen. Future measurements of C-14 and Be-10 in glacial ice dating from this period should help to determine if such an event actually occurred. If it did, then C-14 dates on organic matter deposited at this time should be mistrusted.
Schove (1977) warns, in agreement with the above conclusion, that C-14 dates from the mid-Bölling/Agård Interstadial (12,400±100 varve years BP) may be abnormally young. He notes that a geomagnetic excursion occurred about this time (i.e., the G/E/L Excursion) and that during this time the Earth's magnetic field may have been abnormally weak allowing greater penetration of C-14 producing cosmic rays. So some way other than C-14 dating should be found to date organic remains associated with the Terminal Pleistocene Extinction.
* Since the time of this writing, I have adopted the date 12,700 calendar years B.P. (11,000 C-14 years B.P.) as the climax of this megafaunal extinction. PAL 1/18/99
Broecker, W. S., Kulp, J. L., and Tucek, C. S. "Lamont Natural Radiocarbon Measurements III." Science 124 (1956):154.
Martin, P. S. "Prehistoric Overkill." In Pleistocene Extinctions: The Search for a Cause, edited by P. S. Martin and H. E. Wright, Jr. New Haven: Yale University Press, 1967.
Schove, D. J. (Discussion to paper by N. J. Schackleton) Philosophical Transactions Royal Society of London B 280 (1977):181.