Index Fossils 1
In the early 1800s, some observers in Western Europe noticed that certain fossils are usually preserved in sedimentary rock layers that, when traced laterally, typically lie above other types of fossils. Decades later, after the theory of evolution was proposed, many concluded that the lower organism must have evolved before the upper organism. These early geologists did not realize that a hydrodynamic mechanism, liquefaction, helped sort organisms in that order during the flood. [For an explanation, see pages http://www.creationscience.com/onlinebook/Liquefaction2.html#wp1100074 > 186-197 ]
Geologic ages were then associated with each of these “index fossils.” Those ages were extended to other animals and plants buried in the same layer as the index fossil. For example, a coelacanth fossil, an index fossil, dates its layer at 70,000,000 to 400,000,000 years old. [See http://www.creationscience.com/onlinebook/AstroPhysicalSciences27.html#wp4416259>Figure 28 ] Today, geologic formations are almost always dated by their fossil content (a), which, as stated above, assumes evolution.
a. “Ever since William Smith [the founder of the index fossil technique] at the beginning of the 19th century, fossils have been and still are the best and most accurate method of dating and correlating the rocks in which they occur. ... Apart from very ‘modern’ examples, which are really archaeology, I can think of no cases of radioactive decay being used to date fossils.” Derek V. Ager, “Fossil Frustrations,” New Scientist, Vol. 100, 10 November 1983, p. 425
[http://www.creationscience.com/onlinebook/AstroPhysicalSciences27.html#wp1655298>From “In the Beginning” by Walt Brown ]