Forbidden Archeology: The Hidden History of the Human Race

In 1969, Richard Leakey sent samples of the KBS tuff to England for potassiumargon testing. According to E. T. Hall (1974, p. 15), the age obtained was a seemingly impossible 220 million years.

In 1970, F. T. Fitch and J. A. Miller, having received new samples, ran more potassium-argon tests and decided that the KBS Tuff was 2.6 million years old.

In 1972, Richard Leakey discovered the ER 1470 Homo habilis skull. Because the skull came from well below the KBS Tuff, he assigned it an age of 2.9 million years. This was controversial, because it made Homo as old as the oldest Australopithecus.

Results of paleomagnetic studies by Dr. A. Brock of the University of Nairobi confirmed the potassium-argon date given by Fitch and Miller for the KBS Tuff. ( For an explanation of the paleomagnetic dating method, see Section 9.2.10.)

Brock found that samples in and near the KBS Tuff were of normal polarity (Brock and Isaac 1974, p. 346). This was consistent with the potassium-argon date of 2.6 million years obtained by Fitch and Miller, which, if correct, falls in the upper part of the Gauss Normal Epoch (Figure 11.8). Below the KBS Tuff, the samples were predominantly of normal polarity. But Brock also found in this region two short intervals of reversed polarity, which he identified with the Kaena and Mammoth Events (Brock and Isaac 1974, p. 346). This tended to confirm that the KBS Tuff was in the Gauss Normal Epoch and was somewhere between 2.5 and 2.9 million years old.

Figure 11.8. This is the standard paleomagnetic polarity scale (after Wu, X. and Wang, L. 1985, p. 36). Brock and Isaac (1974) believed the polarity sequence at Koobi Fora supported an age of 2.6 million years, in the Gauss Normal Epoch, for the KBS Tuff.

Brock stated that skull ER 1470 came from “a level equivalent to that in which the Kaena and Mammoth events have been identified” (Brock and Isaac 1974, p. 347). He added: “An age of 2.7 to 3.0 Myr . . . is strongly indicated” (Brock and Isaac 1974, p. 347). Referring to the potassium-argon dates by Fitch and Miller, Brock concluded that “in every case the isotopic and paleomagnetic dates are consistent” (Brock and Isaac 1974, p. 347). Brock also found his version consistent with the faunal chronology prepared by Vincent J. Maglio.

Maglio identified marker fossils in the hominid-bearing sediments of the Lake Turkana sites. Skull ER 1470 was found in the zone containing Mesochoerus limnetes, an extinct pig. Maglio compared the pig teeth found at Lake Turkana with those found at the Shungura site in Ethiopia, where it had been demonstrated that the pig teeth increased in size with the passage of time. At Shungura, teeth of the size found at Lake Turkana fell in a time period extending from 1.8 million to 2.7 million years ago.

Maglio (1972, p. 383) noted: “The indicated age range includes the K /Ar date of 2.6 m.y. for the KBS tuff located within the sedimentary unit containing this fauna.” Richard Leakey believed that Maglio’s report supported his position on the ages of the KBS Tuff and the important ER 1470 skull.

But other scientists, who had different ideas about the relative antiquity of Australopithecus and Homo, were not happy about the potassium-argon age of 2.6 million years for the KBS Tuff (Johanson and Edey 1981). They pointed to new faunal studies that seemed to make the KBS Tuff much younger.

Basil Cooke (1976), for example, said the size range of pig teeth from below the KBS Tuff matched that of Ethiopian pig teeth with an age of 2 million years. If this correlation were accepted, the KBS Tuff would have to be less than 2 million years old.

Richard Leakey proposed differential rates of evolution as a possible explanation. Perhaps the pigs at Lake Turkana and their teeth got bigger earlier than those in Ethiopia because of a more favorable environment.

The dispute over the pig teeth and the KBS Tuff was a major topic at a February 1975 conference in London. Fitch and Miller presented the results of new potassium-argon tests, which yielded an age for the KBS tuff of 2.4 million rather than 2.6 million years (R. Leakey 1984, p. 167).

Another group of scientists showed uranium fission track evidence confirming the new potassium-argon date of 2.4 million years (R. Leakey 1984, p. 168). When uranium 238, a radioactive element, decays into lead, particles released during fission leave tracks in zircon crystals. By measuring the amount of uranium and counting the tracks in the crystals, one can estimate the crystals’ age.