Realitive dating

You might find a small number of 78s for a long period after they were pretty much done.

To start out, we will take a sample of the deposits in each of junkyards.

It isn't possible to investigate all of a junkyard, so we'll pick a representative sample of the deposit.

For a study we're doing on, say, the availability of music in rural locations during the 20th century, we'd like to know more about the deposits in these illicit junkyards.

Using seriation at our hypothetical junkyard sites, we will try to establish the chronology--the order in which the junkyards were used and closed.

But you would never have any 78s in junkyards closed before they were invented.

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).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.He assumed that the change in styles was an evolutionary one, and, if you could quantify that change, he surmised it might be used to indicate which cemeteries were older than others.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.We count the types of musical recording methods found in each of our junkyard samples, and then work out the percentages.When Hi, Why ‘who’ is used instead of ‘that’ in the following sentence?