Bimini Road - Age of The Bimini Road

Age of The Bimini Road

Attempts have been made to determine the age of the Bimini Road using different techniques. These include direct radiocarbon dating of the stones composing the Bimini Road and Uranium-thorium dating of the marine limestone on which the Bimini Road lies.

In 1978, the radiocarbon laboratory operated by the Department of Geology at the University of Miami dated samples from a core collected by E. A. Shinn in 1977 from the Bimini Road. In 1979, Calvert and others reported dates of 2780±70 (UM-1359), 3500±80 (UM-1360), and 3350±90 (UM-1361) from whole-rock samples; a date of 3510±70 (UM-1362), from shells extracted from the beachrock core; and dates of 2770±80 (UM-1364) and 2840±70 (UM-1365) from carbonate cementing the beachrock core. These dates are temporally consistent in that the shells composing the beachrock core from the Bimini Road dated older than the cement holding them together as beachrock. These dates can be interpreted as indicating that the shells composing the Bimini Road are, uncorrected for temporal and environmental variations in radiocarbon, about 3,500 years old. Because of time-averaging and other taphonomic factors, a random collection of shells likely would yield a radiocarbon date that is a few hundred years earlier than when the final accumulation of shells, which were cemented to form beachrock, actually occurred. The radiocarbon dates from the cement demonstrate that the beachrock composing the Bimini Road formed about 2,800 radiocarbon years ago by the cementation of pre-existing sediments that accumulated about 1,300 years earlier. Compared to the dates from the shells and the cement, it appears that the whole-rock dates reflect samples containing varying proportions of shell and cement without any significant contamination by younger radiocarbon. Both these dates and interpretation are consistent with the detailed research by Davaud and Strasser that concluded that the layer of beachrock composing the Bimini Road formed beneath the surface of North Bimini Island and was only exposed by coastal erosion about 1,900 to 2,000 years ago.

Proponents of the Bimini Road being a manmade feature argue that these radiocarbon dates are invalid because they were obtained entirely from whole-rock samples and subject to contamination from younger carbon. The background data reported by Calvert and others concerning the radiocarbon dates from the Bimini Road demonstrate that not all of these dates come entirely from whole-rock samples. That the dates from the shells and the clearly younger cement holding them together as beachrock are temporally consistent argues against any signification alteration of their radiocarbon content. In addition, other studies using radiocarbon dating to study sea level and the age of sediment and beachrock within the Bahamas have not reported any significant problems with contamination by younger radiocarbon. In their detailed research, Davaud and Strasser accepted the radiocarbon dates obtained from the beachrock composing the Bimini Road from the radiocarbon laboratory at the University of Miami as valid indicators of its age.

Gifford and Ball attempted to establish a minimum age using uranium-thorium dating for the Bimini Road by dating a whole-rock sample of the marine limestone (biopelsparite) that underlies the beachrock that composes the Bimini Road. They described this sample as being "Whole rock marine limestone under beachrock off Paradise Point, North Bimini; some recrystallization." This sample yielded a uranium-thorium date of 14,992±258 BP (7132-19/2). Supporters of the idea that the Bimini Road is a man-made structure frequently cite this date in support of it being artificial.

The uranium-thorium date published by Gifford and Ball is regarded as an invalid and meaningless date for two reasons. First, the sample being partially recrystallized means that this limestone was not a closed system as required for a meaningful uranium-thorium date. As a result, this specific date is only an apparent date that completely lacks any scientific value for interpreting the age of marine limestone underlying the Bimini Road. Currently, specific species of corals and mollusks that can be demonstrated to lack any recrystallization using petrographic and X-ray diffraction techniques are the preferred samples for dating. Any limestone sample that shows the least amount of recrystallization is now regarded as incapable of yielding a scientifically valid date and not even worth an attempt at dating. Finally, it is well documented that about 15,000 calendar years ago, sea level in this region was between 95 and 100 meters (312 and 330 feet) below present sea level. As a result, the location from where Gifford and Ball collected the sample of limestone was between 90 and 95 meters (295 and 312 feet) above sea level at the time indicated by the uranium-thorium date of 14,992±258 BP (7132-19/2). Therefore, it is physically impossible for the marine limestone underlying the Bimini Road to have accumulated around 15,000 BP. Thus, this uranium-thorium date is a meaningless, invalid date lacking any scientific significance. Because this date clearly lacks any scientific meaning, geologists and archaeologists rarely mention it in their discussions of the Bimini Road. The marine limestone underlying the Bimini Road dates to the Sangamonian Stage, the last interglacial, when sea level was last high enough for the marine sediments, now lithified into limestone, to have accumulated.