Starting from the 18th Century, scientist had been able to provide methods of knowing the world’s prehistory. One of this is the use of fossils to determine the relative age of strata. Fossils are the remains of living organisms that had lived long time ago while strata are the geological divisions each made out of contiguous layers that exhibits consistent characteristics. Comparing the sets of fossils that exist within different localities gives a hint for geologist whether the layers concerned are of the same strata or not.
The relative age of the localities could be based on the fossil’s relative age that is then determined through carbon dating. As scientist had established that fossils of a certain organism had lived within a certain span of time, it is then compared to other organism which would be also found out to have lived within that same time span. Their similarities would be drawn out that made possible the broader division of the Earth’s history into Eras namely the Cenozoic Era or the Age of Recent life, Mesozoic Era or the Age of the Medieval Life, and the Palaeozoic Era or the Age of the Ancient Life.
Each of them would be further divided into Periods, which is then based on the disturbances that had been theorized to shape the earth’s crust. The time span that is believed that no fossils can be found out is called the Precambrian Period. In analyzing figure 3. 6, we could tell that the three localities though bordered many kilometers apart, have fossil assemblages because almost all of them have Dictyoclostus americanus from the Pennsylvanian Period, Prolecanites gurleyi from Mississippian Period, Palmatolepus unicornis from Devonian Period and Bathyurus extans from Ordovian Period.
This states that the three localities had been for some time span or period had been part of the earth’s outer crust. Though locality 3 had Stratum D and Prolecanites gurleyi missing, this that not means that locality 3 does not exist as part of the earth’s crust because either stratum D was never deposited there or it may had been there but then removed through erosion. The boundary between C and E then would be a disconformity.
References Index Fossils. Retrieved June 6, 2008 from http://pubs. usgs. gov/gip/geotime/fossils. html