Carbon-14 Dating: an Invaluable Yardstick in the Chronology of Humans
Archeologists use many methods to analyze data from the past. One scientific tool they use is to analyze the radioactive decay of chemical elements found in plant and animal remains, pottery, and even in rocks. Radiocarbon dating, also known as carbon-14 dating, has been one of the most important radioisotope dating methods used. This scientific tool, which was first developed by Willard F. Libby in the late 1940s, has significantly improved the accuracy of assigning dates to past events and artifacts as far back as 70,000 years. It is helping archaeologists, geologists, and anthropologists reconstruct the world’s history by filling in some of the many blank dates in the chronology of the history of our human world and by substantiating and revising other dates. In 1941, the radioactive atom, carbon-14, was isolated and discovered. Utilizing this discovery of the unstable radioactive isotope of carbon, Libby formulated an idea for using the decay rate of this radioactive form of carbon to date the remains of once-living plants and animals such as charcoal, wood, bone, shells, and fossils. In 1948, while at the University of Chicago, he and his colleagues started experimenting with carbon-14 as a means for dating the past. The scientists proved that carbon-14, which is present in our atmosphere as carbon dioxide, is absorbed by plants, animals, and human beings at a constant rate, and that the amount of carbon-14 is stabilized at a specific amount. A living organism can only intake a finite amount of carbon-14. Then, at the moment the living organism dies, it stops taking in any carbon-14, and the carbon-14 remaining in the organism starts to disintegrate at the half-life rate of 5,568 years (Poole 1961:27). (Today, based on refined calculations/techniques the half-life rate of carbon-14 is generally considered to be 5,730 years) (Wheatley 2004:98; DeYoung 2005:46). From the experimental results, Libby devised an apparatus to measure the amount of carbon-14 that had been lost and the amount that still remained in the substance. He planned to calculate the age of an object from the amount of carbon-14 left inside it after death. To test the validity of his carbon-14 counting device and subsequent calculations, Libby tested many items that archaeologists had previously dated. Some of the items he tested included: acacia wood from the first stepped pyramid tomb of Egyptian ruler Zoser (established rate: 2700 B.C.; Libby date: 3979±350 years), cypress wood from the tomb of Sneferu in Egypt (established date: 4,575 B.P.; Libby date: 4802±210 years), cedar wood from the Egyptian pharaoh Sesostris’s funeral boat (established date: 3750 B.P.; Libby 3621±180 years), wood from a mummy coffin from the Ptolemaic period in Egypt (established date: 2280; Libby 2190±450 years), wheat and barley seeds (established date: 5000 years old; Libby date 5256±230 years), and lastly, Libby dated charcoal from Iraq at 6596± 360 years which coincided with the known approximate date (Poole 1961:28-32, Libby 1952:70). Except for the Zoser sample date, which dated too far back in history, his experimental dates were accurate within an acceptable margin of error. These sample tests, along with many others, confirmed that his carbon-14 test dating method was scientifically dependable within an acceptable margin of error for objects already dated. Libby then continued his work on dating objects for which no dates had been established. Scientists and scholars began to send him samples from all over the world to radiocarbon date. This included dating artifacts from the Dead Sea Scrolls, Pompeii, Stonehenge, and New Mexico. One of his most significant results occurred when his colleagues dated glacial debris near Two Creeks, Wisconsin. His scientific work provided strong evidence that the last Ice Age in North America had covered the land as recently as 11,000 BCE years...
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