CompuServe Messages

Much of the dating is derived from analyzing the ratios of C12 and C14, carbon isotopes found in organic matter. Carbon14 has a 1/2-life of 5,600 years if memory serves. C14 is incorporated in the organism while it is living and once biological processes stop (death), no additional C14 is picked up. By measuring the amount of C12 and C14, it is possible to determine the age of the organic material. Then one has the age (roughly) of the soil laying on top of the fossil. It can be (and usually is) much more complicated to determine the age of a geological event such as glaciation. Often a variety of methods must be used to establish the chronology of climatic events. Glacial, and other, lakes often display a distinct layering of sediments called varves, in which an alternating pattern of light and dark layers are laid down. These layers represent seasonal patterns, essentially summer and winter. The layers can be extremely thin. You can envision them as similar to tree rings. If you can establish a geological time within the varves, by using an index fossil, carbon dating, or dating volcanic ash, then you can count the "rings" and determine the length of time the lake was in existence. This is only a very brief description of how some dating is done. I'll be glad to add more if you want. Michael