In 1769 in a little town in Oxfordshire,England, a childwith the very ordinary name of William Smith was born into thepoor family of avillage blacksmith. He received rudimentary village schooling,but mostly heroamed his uncle's farm collecting the fossils that were soabundant in therocks of the Cotswold hills. When he grew older, William Smithtaught himselfsurveying from books he bought with his small savings, and at theage ofeighteen he was apprenticed to a surveyor of the local parish. Hethenproceeded to teach himself geology, and when he was twenty-four, he wenttowork for the company that was excavating the Somerset Coal Canal in the southofEngland.
This was before the steam locomotive, andcanal building wasat its height. The companies building the canals to transportcoal neededsurveyors to help them find the coal deposits worth mining as wellas todetermine the best courses for the canals. This job gave Smith anopportunityto study the fresh rock outcrops created by the newly dug canal. Helaterworked on similar jobs across the length and breadth of England, all thewhilestudying the newly revealed strata and collecting all the fossils hecouldfind. Smith used mail coaches to travel as much as 10,000 miles per year.In1815 he published the first modern geological map, “A Map of the StrataofEngland and Wales with a Part of Scotland,” a map so meticulouslyresearchedthat it can still be used today.
In 1831 when Smith was finally recognizedby the GeologicalSociety of London as the “father of English geology,” it wasnot only for hismaps but also for something even more important. Ever sincepeople had begun tocatalog the strata in particular outcrops, there had beenthe hope that thesecould somehow be used to calculate geological time. But asmore and moreaccumulations of strata were cataloged in more and more places, itbecame clearthat the sequences of rocks sometimes differed from region to regionand thatno rock type was ever going to become a reliable time marker throughoutthe world. Even without the problem of regional differences, rocks presentadifficulty as unique time markers. Quartz is quartz—a silicon ion surroundedbyfour oxygen ions—there’s no difference at all betweentwo-million-year-oldPleistocene quartz and Cambrian quartz created over 500million years ago.
As he collected fossils from stratathroughout England,Smith began to see that the fossils told a different storyfrom the rocks.Particularly in the younger strata, the rocks were often sosimilar that he hadtrouble distinguishing the strata, but he never had troubletelling the fossilsapart. While rock between two consistent strata might in oneplace be shale andin another sandstone, the fossils in that shale or sandstonewere always thesame. Some fossils endured through so many millions of yearsthat they appearin many strata, but others occur only in a few strata, and afew species hadtheir births and extinctions within one particular stratum.Fossils are thusidentifying markers for particular periods in Earth's history.
Not only could Smith identify rock strataby the fossils they contained, he could also see a pattern emerging: certainfossils always appear in more ancient sediments, while others begin to be seenas the strata become more recent. Byfollowing the fossils, Smith was able toput all the strata of England's earthinto relative temporal sequence. About thesame time, Georges Cuvier made thesame discovery while studying the rocksaround Paris.
Soonit was realizedthat this principle of faunal (animal) succession was valid notonly in Englandor France but virtually everywhere. It was actually a principleof floralsuccession as well, because plants showed the same transformationthrough timeas did fauna. Limestone may be found in the Cambrian or—300 millionyearslater—in the Jurassic strata, but a trilobite—the ubiquitous marinearthropodthat had its birth in the Cambrian—will never be found in Jurassicstrata, nora dinosaur in the Cambrian.