Carbon dating so frequently used archaeology
It isn't possible to investigate all of a junkyard, so we'll pick a representative sample of the deposit.We take our samples back to the laboratory, and count the kinds of artifacts in them, and discover that each of the junkyards have broken pieces of musical recording methods in them--old broken records, pieces of stereo equipment, 8-track cassette tapes.Absolute dating techniques were not available to him (radiocarbon dating wasn't invented until the 1940s); and since they were separately excavated graves, stratigraphy was no use either.Petrie knew that styles of pottery seemed to come and go over time--in his case, he noted that some ceramic urns from the graves had handles and others had just stylized ridges in the same location on similarly shaped urns.One early recording method consisted of large plastic disks which could only be played on a huge device called a gramophone.
Petrie's notions about Egyptology, and archaeology in general, were revolutionary.The gramophone sat in your parlor and certainly couldn't be carried along with you and your earbobs. When 78 rpm records first appeared on the market, they were very rare.When they became popularly available, you could find them everywhere; but then the technology changed and they became rare again. Archaeologists investigate trash, not shop window displays, so we measure things when they are discarded; in this example, we're going to use junkyards.Next, we break apart the bars and align them so that all of the same colored bars are positioned vertically next to the others.Horizontally, the bars still represent the percentages of musical recording types in each of the junkyards.
The same is true for 45s, and 8-tracks, and cassette tapes, and LPs, and CDs, and DVDs, and mp3 players (and really, any kind of artifact).