After death, radiocarbon disappears at a rate of speed that can be measured. This rate may seem strange to most laymen. It is based on what physicists call “half-lives.” The half-life of radiocarbon is 5,568 years, give or take a few. This means that after 5,568 years, half the radiocarbon is gone. If the material weighed a pound at the death of the plant or animal, only half a pound would be left. After another half-life of the same length, only a quarter of a pound would remain. And so on and so on. With highly refined techniques, what is left of this radioactive substance can be detected in matter 60,000 to 70,000 years old,[20] and it can be measured and its age determined, with a few percentage points of error, up to at least 50,000 years ago. The scientist must be sure, however, that the material—such as wood, charcoal, peat, antler, shell, bone, or hair—has not been exposed to contamination that would add radiocarbon. This method of dating, developed by Willard F. Libby in the late forties, supplied archaeologists with fairly close estimates of the age of sites containing wood, charcoal, shell, or bone. Neanderthal is the first of our early men to have lived within the range of radiocarbon dating. To be more precise, his Mousterian culture has left traces that can be measured. We have several radiocarbon measurements that tell us how recently Neanderthal was around; his oldest cultural materials are beyond the present range of radiocarbon measurement. At Godarville, Belgium, Mousterian artifacts were found underlying an accumulation of peat that dated from more than 36,000 years ago. Since the stone tools were deposited before the peat, they must be at least as old. Charcoal from an ancient hearth in a Libyan cave at Haua Fteah, associated with Levalloiso-Mousterian materials and about three feet or so above a Neanderthaloid jaw, was dated at 34,000 years, or possibly older. The archaeology of this cave suggests that the Neanderthal survived in North Africa until about 30,000 years ago. In Israel, south of Haifa in the Mount Carmel range, at a site called Mugharet-el-Kebara, a very small sample of charcoal, thought to correlate with a nearby Levalloiso-Mousterian deposit, furnished a date of more than 30,000 years.