GEOL 104 Lecture : GEOL 104 Lect13
17 Feb 2012
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Index fossils - represent best fossils for correlation; they are widespread geographically and are limited to a short time span. Assembledge of fossils with overlapping time ranges may be useful if no index fossils are present. People have used various methods to uess the age of the earth such as. The speed at which rivers brought salt to the sea. Becqueral found photographic plates darkened by uranium salts, and this property was termed radioactivity. It was then discovered that radioactivity gives off heat. Boltwood used this process to date rocks - but he did not know all of the complications associated with radiometric dating. The parent atom, p, decays into daughter atom, d. The radioactive decay rate is an exponential constant. By measuring the amounts of p and d at the present time, rock"s age can be determined. Decay rate must be constant throughout time and in variable conditions. No daughter atoms present at the time of formation.
