Dating Kabwe 1, the Broken Hill skull from Zambia
Why is Homo heidelbergensis so much younger than previously thought?
Christopher G. asked about a revised date published in April 2020 for the Broken Hill Skull found in Zambia in 1921. He referred to a report from Gizmodo magazine “Humanity’s Origin Story Just Got More Complicated”,1 and included the following extracts from the article:
“In a new Nature paper co-authored by Chris Stringer from the Natural History Museum in London and Rainer Grün from Griffith University in Australia, a hominin skull found buried in a Zambian cave back in 1921 has been re-analyzed and given a new age of 299,000 years old, give or take about 25,000 years. Known as the Broken Hill skull, it’s about 200,000 years younger than the previous best estimate.”
“Scientists had struggled to date the Broken Hill skull owing to the absence of sedimentary material from the original site in Zambia, which was eventually destroyed and turned into a quarry. The researchers used direct uranium series dating on the skull to come up with the revised date. They also analyzed material that had been scraped off the skull years ago and promptly misplaced. Stringer said this ‘thin mineral coating’ was only recently discovered in the London Natural History Museum’s mineralogy collection, not in his department’s collection ‘where we had been looking for years,’ he told Gizmodo.”
Christopher’s question was, “Why does an archaeological sample provide different dates through uranium dating. And why was the ‘thin mineral coating’, briefly mentioned in the article, responsible for a such a revised date?” Please help.
CMI’s geologist Dr Tasman Walker responded (edited for the web):
Thank you for your email and your question to CMI.
Principles of dating
The issue of dating is confusing to many people because they do not appreciate that researchers can essentially get any ‘date’ they like depending on what sort of date they are looking for. The dates they obtain depend on the samples they select, the sort of sample processing they undertake, the dating methods they use, and the way they interpret the results. And of course, that is all very much driven by their belief system, or worldview.
It is important to appreciate the basic principles of dating, which are not complicated. Creation.com has many helpful articles on this topic (see the articles linked below).
The article The fatal flaw with radioactive dating methods illustrates very simply using a wristwatch why it is impossible to measure a date in the past, when we can only make observations in the present. The precision and sophistication of the measuring instrument is irrelevant because we cannot go back in time to make the needed measurements in the past.
Another article that illustrates the same point using a dripping tap is How dating methods work. This article also includes a real-life example of how evolutionary scientists kept changing the ‘date’ of a skull from Africa until it agreed with what everyone thought was acceptable.
Another important article, Radioactive dating methods: Ways they make conflicting results tell the same story, explains that all ‘dates’ are interpreted. It is a mandatory part of the process. This is where the scientist invents a story about the date such that it gives the impression that, even when the ‘dates’ are vastly different, they appear to be in agreement.
And for a summary of a few dating methods used for archaeology and the problems with them see The dating game. In addition to those in this article there are dozens and dozens of different methods that are used, many of which are discussed on creation.com. However, they all have the same fatal flaws described in the above dating articles.
Answers change as thinking changes
So, why does uranium dating provide different dates? Basically, it comes back to what date the researchers were looking for. This does not imply conspiracy or fraud. Rather, based on their worldview, their research network, and the latest thinking on the subject, the researchers have a view on what sort of dates to expect. And so, they plan and organise their research along those lines.
The article The dating game shows how the acceptable date for a human skeleton at Lake Mungo, Australia, gradually increased over the years. The changes were gradual because researchers in the area of human evolution all over the world needed to adapt in their thinking, which is why it took many decades.
So, how were the different dates for ‘Mungo Man’ obtained? As thinking changed, researchers decided to use different samples, different preparation methods, and different dating systems, which gave different dates. In every case they would explain why the earlier estimates needed to be revised. However, no-one knows without question how the different elements and isotopes were incorporated into a sample. Dating calculations are based on models which assume how all this happens. And so, whenever a sample is tested, the researchers are quite excited to see what the result will be. Then they must decide whether they can develop a plausible story about it, and if it will be sufficiently robust for them to publish it.
You inquired as to why the ‘thin mineral coating’ mentioned in the article was responsible for such a revised date? I have not read the papers associated with this latest report, and so I am not familiar with the details of the dating process they used. The coating would have been deposited on the skull long after death. Since the skull was discovered in an ore pocket in the lead and zinc mine, it is not surprising that it had a mineral coating. And the presence of lead would have affected the isotopic composition of the coating, affecting the calculated ‘date’. Further, it is common for different parts of a sample (e.g. of a skull) to give different results, even with the same dating method. For example, different parts of the bone sample (e.g. hard parts, porous parts, mineral coatings) will usually give different ‘dates’. When the bone is treated to remove, for example, some of the material that has been absorbed into it or deposited onto it, it will give a different result. This affects the sort of sample that is selected, and the pre-processing that the researchers apply. And it affects how they will interpret the result and the conclusions they will develop. Usually, this is meticulously recorded in their paper.
Like you, the researchers will ask themselves the same question, “Why are the results different?” This will lead them to develop plausible explanations, which they will publish in their paper with their results. Perhaps the bone was buried, and minerals were absorbed into it, or certain elements were leached out of it, or the cave was flooded, or a certain coating was deposited on it. The researchers must decide which minerals, which elements, and which isotopes were moved out of the sample, which ones move in, and which ones stayed in place. And they will seek to explain why. Remember, the researchers were not present to see these events and processes happen, or to make measurements. All these explanations are called hypotheses, or guesses. And this is part of the subjective process of obtaining a ‘date’.
Reason for the difference?
The new date published was 299,000 years. Media reports said the “previous best estimate” was 500,000 years, making the new date 200,000 years younger, which is an enormous difference. However, the Nature paper2 did not say “previous best estimate” but that the skull was “often estimated to be around 500 thousand years old,” which is a curious way of putting it. That implies that different ‘dates’ were often estimated for the skull, which reveals the subjective nature of the dating game.
In 2019, before this latest date was published, the Smithsonian website said the skull was between 300,000 and 125,000 years.3 Now the Smithsonian website has the new Nature dates, saying the skull is “between 324,000 and 274,000 years old.”4 Encyclopedia Britannica reports that prior to the 1970s, the skull was said to be only 30–40,000 years old,5 which looks to me like the usual upper limit for carbon dating. The same article says, “The age of the remains is difficult to establish, but animal fossils also found at the site imply a date of 500,000 to 300,000 years ago.”4 In 1974, Bada et al. in their words “tentatively assigned an age of about 110,000 years” to the skull based on aspartic acid racemisation.6 Clearly, there have been lots of different dates put forward for this skull. I have not read the recent Nature paper, but I would expect they would include an explanation as to why they think the previous dates were so different from their estimate, and why their date should be accepted.
We recall Proverbs 18:17 which says, “The one who states his case first seems right, until the other comes and examines him.” In other words, to properly understand the reasons for these differences, it would be necessary to understand how each date was decided, including the methods and assumptions. This would require digging out the relevant scientific papers and supporting documents for all the different estimates. I expect that some researchers will do that, and it would be nice if some creationist researchers would check it too.
Behind all this is a human/political motivation, which means there may also be personal reasons behind this that are not obvious on the surface. Why was it decided to spend the time, effort, and money redating a skull which was discovered some 100 years ago? Is there an agenda involved? Was the older date causing problems with a favoured scheme of evolution, such that it was no longer fitting the narrative? One report I saw by HeritageDaily said, “The research also suggests that human evolution in Africa around 300,000 years ago was a much more complex process, with the co-existence of different human lineages.”7 In recent decades the prevailing “Out of Africa” paradigm has been losing popularity while a global multiregional paradigm has been gaining (see ‘Out of Africa’ on the ropes: The favoured story of evolution is now struggling). Is this dating work part of a thrust to advance a new paradigm? Or, are the researchers simply content with the publicity from reporting such a different ‘date’?
Most people who see the latest media report with its date for the skull will just assume the date is true. They will be unaware of the debate about the date that has been going back and forth for 100 years. They will not know that there have been all sorts of different dates published as the latest ‘absolute truth’, only to be tossed aside. Based on this history of fossil dating, this latest number is unlikely to be the end of the story for the evolutionary establishment.
A biblical perspective
All the above has viewed the situation from an evolutionary, long-age perspective. Let us now begin with the true history of the world and look briefly at this skull from a biblical angle. As you would be aware from the reports, the ‘Broken Hill skull’, which is classified as Homo heidelbergensis, was found in limestone caves at Kabwe, Zambia. Caves generally formed very late in Noah’s Flood (see e.g. The age of the Jenolan Caves, Australia), which ended in real time about 4,500 years ago. This date has been well established by eyewitness reports contained in the Bible (e.g. Genesis 5). Documented reports from eyewitnesses are the most reliable way of knowing what happened in the past, and when.
Creation scientist Peter Line in his article Paleoanthropology in Australia—Homo erectus and modern human origins says most creationist models acknowledge Homo erectus as definitely human. Peter suggests that ‘robust’ humans such as Homo erectus, Homo heidelbergensis and Neanderthals were different from modern humans (particularly in the skull) because they developed differently in the early post-Flood period, which may have been linked to their living longer.
So, we would interpret this skull as that of a human descended from the eight people that came off Noah’s Ark (Genesis 8:18–19). Over hundreds of years, as the population grew after the Flood, some people would have migrated to the area in Zambia (Genesis 10:32). In fact, migration likely occurred after the dispersion at the Tower of Babel (Genesis 11:1–11). This person may have died outside the cave and been buried there after death, although there would be other possible scenarios that could be explored.
So, you can see that there is a lot involved with the ‘scientific’ dating process. It is not a straightforward, objective, value-free measurement. Because ‘dates’ are not objective facts but selected and assigned by the researcher, they are driven by the researcher’s beliefs, goals, and knowledge. As we have seen, the dates keep changing, and they will keep changing as old researchers retire and new researchers come on-line, bringing different beliefs, goals, and knowledge to the enterprise.
Scientist who hold to the history of the earth as revealed in the Bible have a different worldview. They develop a different narrative to explain the evidence, as I have illustrated for the Kabwe 1 skull found in Zambia. Biblical history provides a coherent big-picture framework that allows scientific scenarios to be developed. These scenarios enable research projects to be undertaken to investigate the world and make sense of it, all based on its true history.
Thanks for your question. I hope this response has been helpful.
Dr Tasman Walker
Scientist, Writer, Speaker
Creation Ministries International (Australia)
References and notes
- Dorvsky, D., Humanity’s Origin Story Just Got More Complicated, Gizmodo, 2 April 2020, gizmodo.com.au. Return to text.
- Grün, R., et al., Dating the skull from Broken Hill, Zambia, and its position in human evolution, Nature 580: pp. 372–375, 2020, published online 1 April 2020, https://www.nature.com/articles/s41586-020-2165-4, doi: 10.1038/s41586-020-2165-4. Return to text.
- Kabwe1, Smithsonian National Museum of Natural History, Internet Archive, 9 October 2019, https://web.archive.org/web/20191009122649/http://humanorigins.si.edu/evidence/human-fossils/fossils/kabwe-1. Return to text.
- Kabwe1, Smithsonian National Museum of Natural History, accessed 20 April 2020, http://humanorigins.si.edu/evidence/human-fossils/fossils/kabwe-1. Return to text.
- Kabwe cranium, Encyclopedia Britannica, accesses 20 April 2020, https://www.britannica.com/topic/Kabwe-cranium Return to text.
- Bada, J,L., and three others, Concordance of Collagen-Based Radiocarbon and Aspartic-Acid Racemization Ages, PNAS 71(3):914–917, 1 March 1974; https://doi.org/10.1073/pnas.71.3.914. Return to text.
- Dating of Broken Hill skull leads to questions over modern human ancestry, Heritage Daily, >https://www.heritagedaily.com/2020/04/dating-of-broken-hill-skull-leads-to-questions-over-modern-human-ancestry/127136. Return to text.