No, this is not a theme of techniques to use in your social life. We'll venture into science, and look at some of the techniques scientists use to determine the ages of ancient objects. It's about time.
A web-writer comments, "Until recently, all dating was relative except where links with historical events could be proved. … Chronometric dating has developed in the last 30 years and has revolutionized archaeology."
relative dating – any dating method which sequences things or events relative to each other (earlier, later, or contemporary) but does not tie them to calendrically measured time. It does not give a date in terms of "___ years ago".
absolute dating; chronometric dating – any method to determine age with reference to a specific time scale, such as years before present. The date on a coin is an absolute date.
Absolute dating does not mean "precise dating". It usually has a margin of error (a standard deviation), but it has a relationship to the calendar, which relative dating lacks.
– Richard Dawkins, The Blind Watchmaker [etc.]
… if we are concerned to interpret Aristotle's philosophical views, then it may well be important to know whether the Eudemian Ethics was written before or after the Nichomachean Ethics, but it will be of far less interest to know that one was written in this year and the other in that. Now it may seem as if we possess a quantity of solid and objective evidence for the relative dating of Aristotle's works. For Aristotle quite often refers to his own writings – he will say, "I have already dealt with this point in such-and-such a place".
– Jonathan Barnes, The Cambridge Companion to Aristotle. (The author adds, in frustrated tone, "But the cross-references are a disappointment and a delusion. If we collect and compare them all, we shall find that they are inconsistent – they imply that A was written before A.")
biostratigraphy – the relative dating of layers of sedimentary rock (strata), based on the fossils each contains. (Our quote uses the term to mean, conversely, the dating of fossils based on rock layers.)
A higher stratum is newer than a lower one at the same site (being formed from sediment laid atop lower layers). It may contain fossils. If a stratum at another site has like fossils, then the two strata are contemporaneous, even if they differ in composition.
–New York Times, April 10, 1999
In 1912 British scientists reported finding the famous "missing link", a humanoid fossil from roughly half-a-million years ago. "While the skull is essentially human," they noted, "the mandible [lower jaw] appears to be that of an ape." In other words, human intelligence developed before human teeth, precisely as Darwin had predicted in his Descent of Man: "The early male forefathers of man were … probably furnished with great canine teeth; but as they gradually acquired the habit of using stones, clubs, or other weapons, for fighting with their enemies or rivals, they would use their jaws and teeth less and less." And how pleasant that these fossils (and similar ones in the next few years) came from East Sussex, thus showing that early man was an Englishman.
Such became the general belief for four decades, so this was an incredibly significant find. But oddly, additional fossils found over those decades were inconsistent with the Sussex fossils. Were there two separate lines of descent?
Finally, in 1953, the truth was uncovered. This Sussex man or "Piltdown Man" was a complete and elaborate forgery. We now know that the skull dates to medieval times; the jaw is orangutan and the teeth chimpanzee, filed to proper shape; all were stained to "age" them. It had fooled most of the scientific community.
The first crack in the case had come in 1949, when fluorine dating showed that the bones were far more recent than had been thought.
fluorine dating – relative dating of bones, based on their fluorine content
[A buried bone gradually absorbs, and combines chemically with, fluorine from groundwater. Hence higher fluorine content means greater age. Because the groundwater's fluorine-concentration (and hence, the absorption rate) varies from time to time and from place to place, this technique provides only relative dating, and only within a single site.]
The next time you come to England we'll drive over to Piltdown. It's not very far and there's a pretty good pub in the village. Then you'll be able to put some flesh on the Piltdown bones, as it were...