The spin axis of the Earth sweeps through one complete rotation in 26, years. So the position of the Celestial North Pole changes with time, and this is what Kate Spence tried to use, to work out when the pyramids were built. For a few hundred dollars, you can get a computer program that tells you the positions of the stars, at any point in time.
NOVA Online/Pyramids/How Old Are the Pyramids?
In the year BC when building pyramids was all the rage , two stars appeared to rotate around the Celestial North Pole. Back in BC, it would be quite easy to find True North. All you'd have to do would be to build some scaffolding, and hang a string with a heavy weight.
This would hang perfectly vertically, pointing to the centre of the Earth. You'd then wait until these two stars were vertically aligned exactly with your hanging string.
Then a line from you, to the hanging string, would point due north to the horizon. But Kate Spence also realised that this method of finding True North would work only in that year - because the spin axis of the Earth is slowly sweeping out a great circle over some 26, years.
Great Pyramid of Giza
If you use that method before BC, you'd be slightly to the west of True North and after that date you'd be to the east of True North. Spence looked at the Pyramids of Giza, she found exactly this relationship - the earlier ones were lined up slightly to the west, and the later ones slightly to the east.
It could be that this is just a coincidence - after all, she was looking at only half a dozen pyramids. That's a very small sample size. But if her method is correct, it means that we can calculate the dates when the pyramids were built to within five years or so - which is much better than the currently accepted hundred-year error. Perhaps the only real error the Egyptian pyramid builders made was forgetting to install some doors.
Use this form to email 'Dating the pyramids' to someone you know: By clicking 'Send to a friend' you agree ABC Online is not responsible for the content contained in your email message. Skip to navigation Skip to content. This site is being redeveloped. So there's no one easy way that we know what the date of the pyramids happens to be.
It's mostly by context. The pyramids are surrounded by cemeteries of other tombs. In these tombs we find bodies. Sometimes we find organic materials, like fragments of reed, and wood, wooden coffins. We find the bones of the people who lived and were buried in these tombs. All that can be radiocarbon dated, for example. But primarily we date the pyramids by their position in the development of Egyptian architecture and material culture over the broad sweep of 3, years.
So we're not dealing with any one foothold of factual knowledge at Giza itself. We're dealing with basically the entirety of Egyptology and Egyptian archaeology. Can you give us an example of a single aspect of material culture, from ancient Egypt that you might use as a starting point for dating the pyramids? The pottery, for example. All the pottery you find at Giza looks like the pottery of the time of Khufu, Khafre, and Menkaure, the kings who built these pyramids in what we call the Fourth Dynasty, the Old Kingdom.
We study the pottery and how it changes over the broad sweep, some 3, years. There are people who are experts in all these different periods of pottery or Egyptian ceramics. So to bring it down to a level that almost anybody can understand, if, for example, you were digging around the base of the Empire State Building, assuming that it was a ruin and the streets around it in Manhattan were filled with dirt, and you started finding ceramics that were characteristic of the Elizabethan era or say the Colonial period here in the United States, that would be one thing.
But if you started finding the Styrofoam cups and the plastic utensils of the nearby delicatessen, then you would know by virtue of their position in the overall material culture of the 20th century that that's probably a good date for the Empire State Building. Of course then you'd look at the Empire State Building's style and you'd compare it to the Chrysler Building, and you'd compare it to the Citicorp Building, which is considerably different.
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And you'd work out the different styles in the evolution of Manhattan itself. But by and large, you would, in the broad scope, be able to put the Empire State Building and Manhattan in an overall context of development here in the United States and in the modern 19th and 20th centuries. And you would know that it didn't date, for example, to the colonial period of George Washington and Thomas Jefferson, because nothing you'd find in the Empire State Building ruins, around it, in the dirt surrounding it—maybe it's a stump sticking up above the sloping ruins of Manhattan—nothing really looks like the flowing blue china, or the other kinds of utensils and material culture that they used in the time of the American Revolution.
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. When it comes to carbon dating, do you need organic material? There has been radiocarbon dating, or carbon dating done in Egypt obviously before we did our studies, and it's been done on some material from Giza.
The Age Of The Great Pyramid Of Giza
For example, the great boat that was found just south of the Great Pyramid, which we think belongs to Khufu, that was radiocarbon dated—coming out about 2, B. But how do you carbon date the pyramids themselves when they're made out of stone, an inorganic material? We had the idea some years back to radiocarbon date the pyramids directly. And as you say, you need organic material in order to do carbon dating, because all living creatures, every living thing takes in carbon during its lifetime, and stops taking in carbon when it dies. And then the carbon starts breaking down at a regular rate.
So in effect, you're counting the carbon in an organic specimen. And by virtue of the rate of disintegration of carbon atoms and the amount of carbon in a sample, you can know how old it is. So how do you date the pyramids, because they're made out of stone and mortar? Well, in the s when I was crawling around on the pyramids, as I used to like to do and still do, I noticed that contrary to what many guides tell people, even the stones of the Great Pyramid of Khufu are put together with great quantities of mortar. We're looking, you see, at the core.
A pyramid is basically, most basically, two separate constructions: Since most of the outer casing is missing what you see now is the step-like structure of the core. The core was made with a substantial slop factor, as my friend who is a mechanic likes to say about certain automobiles. First, there are significant discrepancies between the and dates for Khufu and Khafre, but not for Djoser and Menkaure. Second, the dates vary widely even for a single monument.
We have fair agreement for the 1st Dynasty tombs at North Saqqara between our historical dates, previous radiocarbon dates, and our radiocarbon dates on reed material.
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We also have fair agreement between our radiocarbon dates and historical dates for the Middle Kingdom. Eight calibrated dates on straw from the pyramid of Senwosret II BC ranged from years older to 78 years younger than the historical dates for his reign. Four of the Senwosret II dates were only off by 30, 24, 14, and three years. It is likely that, by the pyramid age, the Egyptians had been intensively exploiting wood for fuel for a long time.
Because of the scarcity and expense of wood, the Egyptians would reuse pieces of wood as much as possible. Some of this recycled wood was burned, for example, in mortar preparation. If a piece of wood was already centuries old when it was burned, radiocarbon dates of the resulting charcoal would be centuries older than the mortar for which it was burned. We thought that it was unlikely that the pyramid builders consistently used centuries-old wood as fuel in preparing mortar.
The results left us with too little data to conclude that the historical chronology of the Old Kingdom was wrong by nearly years, but we considered this at least a possibility. Alternatively, if our radiocarbon estimations were in error for some reason, we had to assume that many other dates obtained from Egyptian materials were also suspect. This prompted the second, larger, study. If the Middle Kingdom radiocarbon dates are good, why are the Old Kingdom radiocarbon dates from pyramids so problematic?
The pyramid builders often reused old cultural material, possibly out of expedience or to make a conscious connection between their pharaoh and his predecessors. Beneath the 3rd Dynasty pyramid of pharaoh Djoser, early explorers found more than 40, stone vessels. Did Djoser gather and reuse vases that were already years old from tombs at North Saqqara?
He took pieces of Old Kingdom tomb chapels and pyramid temples including those of the Giza Pyramids and dumped them into the core of his pyramid at Lisht.
Test results from 5th Dynasty pyramid Sahure.