Dating Methods Essay -- essays papers

General Differances Between Relative and Absolute Dating Methods Getting dates for fossils that are found in sites being excavated by anthropologist is very important. Dates show the evolution from early hominid specimens to our own species, Homo homo sapiens. There are many methods that can be used to acquire these dates, but all of these methods fall into one of two catorgories. They can either give a absolute date or a relative date. An absolute date is one in which you get an actual date in years. Also known as chronometric methods. Relative dates do not give an actual date in terms of years, but they tell you if one fossil is older or younger than another fossil. Ushally relative dates are given in terms of the column of earth they are found in. This is called striatigraphy. In sites like Olduvai gorge their are geological layers of vocanic ash and sediment. When a anthropologist finds a fossil in a undistirbed layer of gray ash, you know that it is younger than the fossil in the layer of red ash below, and that fossil is younger than the fossil in the layer of brown ash below it.(Johanson 65) The basic theory here is that a certian site cantians a geolgical column key that is made up of differant strata layers, the fossils get older as they move down the key, and are found in differant layers of strata..(Scully 2) Relative dates have a couple of major problems. One is that the earth moves in many ways and this can distrube the layers of sediment putting younger fossils below older ones. Another is that you can not tell exactly how much younger or older something is from somethinng else and you can not date differant fossils from differant sites with thes relative dating methods. Absolute dating, unlike realative dating, gives the anthropologist an exact date in terms of calander years. These dating methods are much more reliable and can be used in many differant sites with many differant fossils. Absolute dating bases it’s dates on the natural radioactivity of differant elements found in the world.(Johnston 216) There are certian elements that occur in differant forms, these elements are called isotopes. Each one of these isotopes has a differant atomic mass than others. Some of thes isotopes are radioactive, meaning that they give of radiation in either alpha or beta form, as they de... ... has a half-life. C14 is the radioactive isotope of rearular carbon, c12. The cocentration of C14 in the body is one billionth of a gram in the body to one gram of C12. This C14 is contantly decaying, but through animals and plants breathing it is replenashed when an organism is alive. When the animal dies the C14 intake stops and a decay that is not replenashed.(Comas 456) During life an organism have a specific activity of 15.6 disintigrations per minuate per gram of regular carbon in thier body.(Comas 456) â€Å"After life and C14 intake cease and the equilibrium is halted, radioactive disintigration of C14 occurs, and after 5,700 years this activity will have decreased to 7.8 disintigratuions per minuate per gram of carbon in the body.’(Comas 457) This means that the ratio of C14 to C12 left in the fossil when it is found can give a date in years. Carbon-14 dating has a half-life of 5,700 years, with the lower limit of 1,000 years. The upper limit used to be about 30,000 years because after that the ratio was too small to analis. Recently reaserch by Haring and deVires has let scientist put the upper limit at 100,000 years old.(Comas 457)