I noticed that in the interstices between the stones and in this mortar was embedded organic material, like charcoal, probably from the fire that they used to heat the gypsum in order to make the mortar.You have to heat raw gypsum in order to dehydrate it, and then you rehydrate it in order to make the mortar, like with modern cement. And it involved us climbing all over the Old Kingdom pyramids, including the ones at Giza, taking as much in the way of organic samples as we could.We study the pottery and how it changes over the broad sweep, some 3,000 years.There are people who are experts in all these different periods of pottery or Egyptian ceramics.So in effect, you're counting the carbon-14 in an organic specimen.And by virtue of the rate of disintegration of carbon-14 atoms and the amount of carbon-14 in a sample, you can know how old it is.So it's hard to give a succinct answer to that question, because we date things in archaeology on the basis of its context and a broad mass of information and material culture—things that were used by people, styles, and so on.
These were chisels and hammers and you know, people who were really out there.So it occurred to me that if we could take these small samples, we could radiocarbon date them, not with conventional radiocarbon dating so much, but recently there's been a development in carbon-14 dating where they use atomic accelerators to count the disintegration rate of the carbon-14 atoms, atom by atom. We weren't damaging the pyramids, because these are tiny little flecks and it's a very strange experience to be crawling over a monument as big as Khufu's, looking for a bit of charcoal that might be as big as the fingernail on your small finger.We noted, not only the samples of charcoal, sometimes there was reed.We find the bones of the people who lived and were buried in these tombs. But primarily we date the pyramids by their position in the development of Egyptian architecture and material culture over the broad sweep of 3,000 years.So we're not dealing with any one foothold of factual knowledge at Giza itself.