Petrie was a scientific archaeologist, probably close to our first example.The seriation method works because object styles change over time; they always have and always will.Petrie's problem was that he had discovered several predynastic cemeteries along the Nile River in Egypt that seemed to be from the same period, but he needed a way to put them in chronological order.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.By 2100, a dead plant could be almost identical to the Dead Sea scrolls, which are more than 2,000 years old.These well-known “aging” properties of atmospheric carbon were pinpointed for different emissions scenarios in a paper published in the yesterday.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.

A T-shirt made in 2050 could look exactly like one worn by William the Conqueror a thousand years earlier to someone using radiocarbon dating if emissions continue under a business-as-usual scenario.

That is what is happening with the burning of fossil fuels, which are so old they do not contain any carbon-14.

Nonradioactive carbon is now flooding the atmosphere, which creates a dilution effect.

A good example of a change in artifact type is the development of hand-held PDAs from those first enormous cell phones. As an example of how change through time works, consider the different music recording methods that were used in the 20th century.

Scientists use a technique called radiometric dating to estimate the ages of rocks, fossils, and the earth.