Forbidden Archeology_ The Full Unabridged Edition - Michael A. Cremo [409]
In 1983, the original paleomagnetic dating of 1.7 million years for the Yuanmou site, reported by Li Pu and his associates in 1976 and reconfirmed in 1977 by Cheng and his associates, was challenged by Liu Dongsheng and Ding Menglin (Wu, X. and Wang, L. 1985, p. 35). They proposed a different explanation of the magnetostratigraphic sequence at Yuanmou.
According to Wu Xinzhi and Wang Linghong: “Liu and Ding prefer to correlate the normal polarity member at Yuanmou with the Brunhes Epoch rather than with an event of normal polarity within the Matuyama. Furthermore, they have concluded that the layer yielding the fossils of H. erectus is situated at the base of the Brunhes Normal Epoch strata [Figure 9.8] and therefore might not be older than 0.73 million years b.p., and possibly only 0.5–0.6 million years old” (Wu, X. and Wang, L. 1985, pp. 35–36).
Figure 9.8. Cheng et al. (1977) and Li et al. (1976) established a correlation between the polarity sequence at Yuanmou (center) and the standard polarity sequence (left) that gave the hominid-bearing stratum an age of about 1.7 million years. But in 1983, Liu and Ding established a correlation between Yuanmou and the standard sequence (right) that gave the hominid-bearing stratum an age of approximately .73 million years (Wu, R. and Wang, L. 1985, p. 36).
Paleomagnetic dating is based on the assumption that the earth’s magnetic field undergoes shifts in polarity, which are recorded in the magnetic properties of the strata at a site. Upon conducting the required measurements on the strata, one obtains a sequence of normal and reversed polarities, which are grouped into various epochs, such as those named in the above passage (Brunhes Normal, Matuyama Reversed, etc.). The sequence of polarities is typically displayed in a column, with periods of normal polarity shown in black and reversed polarity in white. As can be seen, in Figure 9.8, there may be brief episodes of normal polarity in a reversed epoch and vice versa. One thus obtains a column of many black and white bars, of various thickness, representing the time of each polarity period. One may then compare the polarity sequence from a particular site, which may be quite complex, with the standard polarity sequence and its known chronometric dates. When the site polarity sequence is properly aligned with the standard sequence, one can then assign dates to the various strata at the site by comparison with the standard sequence. The problem is this: matching the polarity sequence obtained at a particular site with the standard sequence is not always easy—there is much room for interpretation, as we can see from the conflicting interpretations of the polarity sequence at Yuanmou.
In 1979, Chinese scientists using amino acid racemization methods dated animal fossils from Yuanmou to 0.80 million years. But Wu and Wang warned: “Fluctuations in average temperature on the enclosing sediments during burial may have had a significant influence on these determinations, and, as such fluctuations are not at present quantifiable, the resulting chronometric dates must be viewed with caution” ( Wu, X. and Wang, L. 1985, pp. 36–37). The inventor of amino acid racemization dating, Bada, admitted that in certain cases the technique did not give reliable dates (Appendix 1.3.5). Wu and Wang stated that the fauna at the hominid site is Early Pleistocene, supporting the paleomagnetic date of 1.7 million years. They thus differed from Aigner, who said the fauna favored an early Middle Pleistocene