Some of the most useful fossils for dating purposes are very small ones.For example, microscopic dinoflagellates have been studied and dated in great detail around the world.Who's on First, University of California, Berkeley. This website is a book chapter about geologic time. This online version of their informative booklet contains short, content explanations about relative time, major geologic time divisions, index fossils for use in age dating, radiometric dating and the age of the earth. This 5-12-grade activity introduces students to the idea of sequencing information in overlapping data sets and the Principle of Superposition, which is a core concept in relative dating. Offers history of age dating, stratigraphic principles, rock correlation, fossil correlations, radiometric dating, and the geologic time scale. Short discussion of radioactive dating and stratigraphic principles. The oldest rocks contained no fossils, then came simple sea creatures, then more complex ones like fishes, then came life on land, then reptiles, then mammals, and finally humans.Since the half-life of 14C is relatively short (5,730 years there should be no detectable 14C left after about 100,000 years.Relative dating is used to arrange geological events, and the rocks they leave behind, in a sequence.The method of reading the order is called stratigraphy (layers of rock are called strata).
Fossils are important for working out the relative ages of sedimentary rocks.The site provides background information about stratigraphic principles and relative time, biostratigraphy (using fossils for relative dating), and radiometric dating. The site also provides fact sheets on the age of the Earth and isochron dating. Some fossils, called index fossils, are particularly useful in correlating rocks.For a fossil to be a good index fossil, it needs to have lived during one specific time period, be easy to identify and have been abundant and found in many places. If you find ammonites in a rock in the South Island and also in a rock in the North Island, you can say that both rocks are Mesozoic.