Lab 8: geologic time (part 2): relative & absolute dating name: section: fossil succession the principle of faunal/fossil succession began with william smith, an english geologist. he stated that the fossils were arranged in a consistent and reliable order in the sedimentary rocks that can be identified around the world. for example, the trilobite paradoxides pinus, which lived during the cambrian, will never be in the same strata as the bothyurus extons, which lived during the ordovician (see figure below). this principle allows for rocks to be dated using the fossils contained within. today, we understand this as the result of evolution; however, this concept was understood in the late 1700's, over 50 years before darwin published his ideas. based on the fossil relationships, you can tell the relative age of the rocks and correlate, or match up, one layer to another across the world. the first, or oldest, strata in which a fossil is found in is called the first occurrence. the last strata, or youngest, that the fossil is found in is called the last occurrence. the sequence of strata in which a particular organism is found, between the first and last occurrences, is called the range zone. this represents a distinct time zone in which the organism lived. for example, the trilobite order harpetida has a first occurrence during the cambrian and a last occurrence at the end of the devonian. therefore, anywhere we find a fossil from this order of trilobites, we know the strata are cambrian to devonian in age. fossils that have a limited range zone, were widely distributed during that time period, and are easily recognizable are called an index fossil or guide fossil. we can use the index fossils to identify the time period that the rocks are from. 01 bas