Other archeologists are beginning to recognize the importance of the eggshells, Miller said. They are now beginning to study owl eggs, which are found at many archeological sites in Northern Europe. Moreover, the research team has found that every other type of bird egg they have studied gives similar results, so those types of shells can be used as well. He found that the eggshells from the site were about 77,000 years old, providing strong additional evidence that modern humans originated in Africa, not on some other continent as some researchers believe.Īlthough ostriches are most common in Africa, ostrich eggs have also been found in China and Mongolia and would be useful for dating there. Miller of the University of Colorado in Boulder, who is also a member of the team, has been studying the remains of unquestionably modern humans taken from the Border Cave on the east coast of South Africa. Dating of eggshells found with them, however, shows that the bones are at least 25,000 years old.Īnthropologist Gifford H. At Ashango in Zaire, for example, researchers have excavated skeletal fragments “which are essentially similar to skeletons of modern East Africans, so they were thought to be fairly recent,” Brooks said. The team has already been using the technique at African sites. In cooler climates, such as China, it can be used on objects 1 million years old. ![]() In the tropics, Brooks and Hare report, the technique can be used to date objects as old as 200,000 years. They found that this racemization reaction proceeds at a steady, predictable rate that can be used for dating as long as it is compared to materials of known age at a given site. #Its shell does not crack crossword series#Hare and his colleagues have done a series of tests with contemporary ostrich eggshells, heating them in the absence of water and determining the rate at which one amino acid, called L-isoleucine, is converted into its D analog. The chief advantage of the eggshells is that the protein they contained is locked into position by the mineral portion of the shell, so it does not easily leach out and contaminants do not easily get in. The Science paper thus represents a rebirth of sorts for the technique. Hence, the technique produces unreliable dates and it has been largely discredited. Indigenous amino acids are readily leached out of the bones by water, and the bones are easily contaminated by amino acids from other sources. Researchers such as Jeffrey Bada of the Scripps Oceanographic Institution in La Jolla originally tried to use this technique to date human and animal bones, but they encountered great difficulties. The rate of this change is constant at any temperature, so by measuring the ratio of D and L amino acids, researchers can determine how long ago the organism died. In nature, virtually all amino acids are present in only one of two possible spatial configurations, called D and L, that have a three-dimensional relationship to each other, similar to the relationship of the right hand to the left.Īfter an animal’s death, the L amino acids will slowly undergo a chemical change to the D-form until a 50-50 mixture of the two forms is present. ![]() ![]() Amino acids are the individual molecules from which proteins are formed. “That is one of the things I am most excited about,” Brooks said.Įggshell dating relies on a physical process called amino acid racemization. ![]() One particular advantage of the new technique is that it is inexpensive, so that a large number of objects at a site can be dated to determine if artifacts from different time periods have been jumbled together by weather, flooding or excavations-a problem that occurs frequently.
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