An Interpretation and Critique of the Radiocarbon Database for Tiahuanaco
By Sean Hancock
"If a C-14 date supports our theories, we put it in the main text. If it does not entirely contradict them, we put it in the footnote. And if it is completely 'out of date', we just drop it."
"Since its development as a dating tool, archaeologists have struggled with the interpretation of radiocarbon data due to its limitations in accuracy and precision"
Alan Kolata, a major authority on Tiahuanaco, rubbishes all arguments that attribute the construction of the site to some forgotten episode and people. For him, along with his distinguished colleagues, such claims simply do not stand up to the rules of evidence. They brand such accounts as myth, racist propaganda and story telling, not grounding for dating stone.
Archaeologists draw their conclusions about ancient sites from the evidence they accrue from controlled excavations. From this evidence they seek to answer a series of questions of which the most important is, when was this site built?
Since the 1950s the radiocarbon dating technique has been incorporated into the archaeologist's arsenal. Radiocarbon dates stand as a scientific endorsement for the official dating of ancient sites and are celebrated by archaeologists as irrefutable dating evidence. And why shouldn't they - who wants to argue with science?
In an earlier article for this Forum What is Radiocarbon Dating and is it a reliable method of dating archaeological sites? I discuss the scientific theory of radiocarbon dating and illustrate how it is a fallible scientific process, ridden with problems. Lets take the discussion to the next level.
An Archaeological Perspective
In the early 1990s Marius S Ziolkowski, a Professor in Archaeology at Warsaw University, set out to bring together and catalogue a Radiocarbon Database for Bolivia Ecuador and Peru. In 1994 he and his colleagues published a 604-page document listing and discussing their results. Today it is very hard book to track down which is a shame as it is a first class piece of scholarly work and remains the authoritative publication in this area.
To complete this work Ziolokowski et al had to wade their way painstakingly through numerous scientific and archaeological publications spanning four decades. They comment:
"In some papers the radiocarbon dates are quoted without laboratory codes and dating errors and a common practice, especially in older papers, is to quote the dates as calibrated dates without indicating the calibration method and specific calibration curve used" 
This is not science. A result is scientific when the procedure is scientific in that it is consistent and clear. A scientific result is also a testable one. How can you test a result when you are at a loss as to how that result came about? Ziolokowski et al wanted to make this clear - they were not happy with the quality of the data they were working with.
Of the two thousand eight hundred dates listed for Bolivia, Ecuador and Peru only twenty-nine of them derive from samples excavated from Tiahuanaco. The standard of the documentation method employed to record the radiocarbon dates from Tiahuanaco by the various laboratories involved, did not live up to my expectations. Sometimes the nature of the sample is given sometimes it is not; sometimes the depth at which the sample was excavated is given sometimes it is not; sometimes the sample is put into an archaeological context, sometimes it is not. It is very difficult data to interpret as you might imagine. It seems that communications between archaeologists and scientists in these instances were not good.
For a radiocarbon date to be taken into archaeological consideration all of the above must be clear. Ziolokowski et al point out that the nature of a sample must be defined so that it can be put in its cultural context - its association with the prehistory of the site must be quantifiable . For about a third of the radiocarbon dates for Tiahuanaco it is not clear what depth the samples were excavated. Why?
For example, the oldest radiocarbon date arrived at for Tiahuanaco is dated to 3530 BP , or 1530 BC. This sample was taken from the Kalasasaya region of Tiahuanaco. The archaeological comment that accompanies this sample reads:
"layer 6.Unexpectedly old compared with Gak-52" .
Gak-52 refers to another sample tested by the laboratory from the same cultural strata. Sample Gak-52 was dated to 240 BC. Unfortunately no archaeological comment accompanies this sample so we must assume that this is the accepted date of occupation for this archaeological stratum. It would seem that the former sample is "archaeologically unacceptable'. If you look at the date lists published in the journal Radiocarbon you will find that this kind of rejection of dates is commonplace. If the dates don't fit the archaeological hypothesis they are simply ignored. Sheridan Bowman, the author of Radiocarbon Dating - Interpreting The Past, argues:
"These 'unacceptable' results perhaps more than any others, need careful consideration" 
Why no explanations for the discrepancy of 1340 years, and why comment on one date and not the other? An explanation for the discrepancy can be postulated. Dating errors aside what if this cultural layer (and possibly others) at Tiahuanaco has been contaminated by the organic composite of other layers? Ziolkowski et al state:
"Admixture of material of different ages may result from activity of small animals, which may transport organic matter between cultural layers or form channels or holes, which are then filled by foreign organic matter of different age" 
They go on to explain that the only way for archaeologists to avoid dating foreign material is for them to recognize such patterns of contamination in the field. The two samples in question were excavated in the late 1950s and no debate about the archaeological significance of mixed cultural layers accompanies them. This represents shabby work. Indeed, Philip Barker in his book Techniques of Archaeological Excavation states:
"It must be established that the object (sample) is not intrusive, that it has not been taken down an animal hole, or slipped down the interstices between the stones of a wall. If there is any doubt about this the object should be rejected for dating purposes". 
Therefore, when analysing radiocarbon dates for ancient sites it is important to scrutinise the collection procedure for the samples. Trenches are dug and samples are collected from different archaeological layers but can we be sure that these layers have not been mixed? Archaeologists would of course argue yes! They say that radiocarbon dates are analysed in their archaeological context. What do they mean exactly by "their archaeological context'?
Garret Fagan in his public attack on Graham Hancock's treatment of radiocarbon evidence for Tiahuanaco states:
"Archaeological context is usually sealed strata of occupation, layer upon layer from the bottom (oldest) levels of a site to the upper (most recent) strata" 
The presence of neat archaeological layers (a requirement for sample association) is not always the case at Tiahuanaco. Above we saw how two samples from the same cultural strata differed in age by 1340 years. The archaeological comment that accompanies another sample tagged P-146 reads:
"A mixed surface level, with classic Decadent, and later pottery" 
So the situation is this: the samples used to date Tiahuanaco have been inconsistently recorded, anonymously calibrated and come from a site that exhibits evidence of mixed cultural layers. And yet they are cited as a solid basis for dating the planning and construction of Tiahuanaco to around the time of Christ . Is it "scientific" to form such bold and certain deductions from such uncertain and unstable evidence?
Looking at the other side of the coin there are instances when the radiocarbon dates for Tiahuanaco are internally consistent. We do not want to be accused of ignoring this fact. Sample Hv-17 was taken from a depth of 50cm under or beside (this is not made clear) the ceremonial platform of Kalasasaya. It was dated to AD 1710. Sample Hv-19 was excavated from the same pit but from a depth of 180cm. Hv-19 was dated to AD 305. Therefore, parts of Tiahuanaco do seem to qualify for radiocarbon analysis - the archaeological conditions are right and there is a satisfactory graduation between the deeper (older) sample and the shallower (more recent) sample.
But these two samples indicate something interesting. If they were excavated from below the ceremonial platform (this must be inferred if they are to be regarded as evidence for dating its construction) then why does one of them date to AD 1710? Nobody would accept this as the date for the construction of the ceremonial platform. Therefore, if it was indeed found under the platform then the 1710 sample is evidence for later alteration of the site, probably by human intervention (18th century treasure seekers?). With this in mind one must ask the question, could the radiocarbon database for Tiahuanaco be as much evidence for alterations made at the site as it is for the absolute age of the site?
Is there any other scrutiny we can apply to the radiocarbon database for Tiahuanaco? I believe so. Since the radiocarbon samples were collected and analysed in the context of the archaeological layers they were taken from, the catalogue of dates reflects the extent and depth of the archaeological excavations carried out at the site. The simple question, therefore, is were the excavations thorough enough to exclude any possibility of an earlier layer of occupation? In short did they dig deep enough? Lets see.
Sample P-123 represents one of the deepest excavated samples from Tiahuanaco. It was found 3.75 metres under ground (at Lat 16 33' S, Long 68 48'W] and it dates to around AD 133 . The archaeological comment for this sample reads:
"Excavation continued to 4.75m with no pottery below 4m" 
So they excavated a further 75cm of soil without finding anything - big deal! Is it so absurd or unscientific to be open minded to the possibility, however remote, that a yet-to-be identified cultural layer exists at Tiahuanaco?
Lets speculate for a moment. If Tiahuanaco is in fact the vestige of a forgotten people then at least a trace of their activities should exist in the archaeological record. No such evidence has been unearthed. However, if that forgotten civilisation was wiped out by some ancient cataclysmic event in the Andes isn't it possible that the site might have remained uninhabited for a period of time, maybe even for thousands of years? During this interval a build up of archaeologically sterile soil would have formed, smothering all evidence of previous human activity. This is the argument put forward by Oswaldo Rivera, former Director of Archaeology of Bolivia, quoted in the Introduction to Graham Hancock's 1998 book Heaven's Mirror:
"We are thinking that Tiahuanaco is so much earlier than has been realised before. After 21 years of making excavations and studies in Tiahuanaco I can tell you we are all the days with out mouths open, because Tiahuanaco is incredible, including for the archaeologists working in Tiahuanaco. We are all the days discovering different things and I am sure we are going to discover the inner part of Tiahuanaco a sunken Tiahuanaco, underneath the existing one I think 12 or 21 metres down we have another Tiahuanaco, and it's the sacred Tiahuanaco, the original. I can't tell how old it is. It's a new chapter in the study of Tiahuanaco. We are going to open a new book'
This essentially is the main problem I have with the radiocarbon database for Tiahuanaco. You could debate infinitely about the problems that archaeologists and scientists encounter in the collection and dating of samples and how these problems can lead to imprecise dates. However, this would be futile. The fact that certain dates may be out by fifty a hundred or even 200 years is not relevant. There are twenty-nine official radiocarbon dates for Tiahuanaco and none of them indicate the existence of human activity beyond 1500BC.
The question we have to ask is whether or not these radiocarbon dates are archaeologically representative? I believe the answer to that question is no. What is called for is a more thorough excavation programme at Tiahuanaco that would once and for all close this case.
Scattered throughout the literature are tight guidelines to achieve the "perfect' radiocarbon motivated archaeological operation.  The excavations at Tiahuanaco and the radiocarbon dates that are their result do not live up to these models and must be viewed with caution as a result.