Homo naledi: The Date

Hawks, John.  “Finding ancient fire use in the Rising Star cave system.”  John Hawks, johnhawks.net.  Dec 7, 2022.  A blog post by a co-leader of the excavations, dated six days after Lee Berger announced the fire evidence in a public lecture on 1 December 2022.  It locates the hearths and explains why the team has not simply radiocarbon-dated the charcoal.

1. 1a.

   Paragraph 18:  “Data that we reported in our 2017 paper helps show why finding a few recent dates doesn't make things easy at all.  Two naledi bones yielded radiocarbon dates between 36,000 and 33,000 BP.  We very much considered whether these naledi bones may actually be this young, and today I still would not categorically rule this out.  However other methods including direct U-series-ESR ages on naledi teeth made the radiocarbon results stand out as inconsistent.  To explain the inconsistency, the team hypothesized that the radiocarbon results reflect contamination by carbon from outside the bones.” ↩ ↩ ↩

2. 1b.

   Paragraph 19:  “The point is, finding a young radiocarbon date may not clarify the situation very much.  Aside from the Dinaledi assemblage, the other naledi discoveries have no geological age estimate yet, including the Lesedi Chamber material.  We cannot assume they are all the same age, and some of them may surprise us.  I keep my mind open to the possibility that additional radiocarbon work may arrive at a young result.” ↩

Pettitt, Paul, and Bernard Wood.  “What we know and do not know after the first decade of Homo naledi.”  Nature Ecology & Evolution 8(9):1579–1583.  2024.  A ten-year review by the Durham archaeologist of burial and the senior hominin taxonomist at George Washington University.  Page numbers below are those of the accepted manuscript, which runs from 1 to 10 and is headed with a working title, "Making sense of the first decade of Homo naledi", and the authors in the other order.  Mirror:  Archive.org

1. 2a.

   Page 3 of the accepted manuscript:  “The minimum age for the capping flowstones is 242±5 ka BP (sample RS18), and the researchers’ best estimate of the age of H. naledi is the maximum US-ESR age, which is 253 +82/-70 ka (Dirks et al., 2017), with a more recent study suggesting the age of the H. naledi remains is between 335 ka and 241 ka (Robbins et al., 2021).  But many of these dates are minimum ages, both OSL and US-ESR can be unreliable, and dates for the formation of flowstones in the chamber suggest ages ranging from 500 ka BP to older than 780 ka.  This current imprecision seriously impedes understanding of the evolutionary position of H. naledi.” ↩ ↩

Dirks, Paul H. G. M. et al.  “The age of Homo naledi and associated sediments in the Rising Star Cave, South Africa.”  eLife 6:e24231.  2017.  The dating paper, twenty authors, six methods.  eLife publishes its decision letter and the authors' response with the paper, and several quotations here are from that exchange.  The paper has no page numbers;  places are its section headings.  Mirror:  PMC ↩

1. 3a.

   Section Abstract:  “By combining the US-ESR maximum age estimate obtained from the teeth, with the U-Th age for the oldest flowstone overlying Homo naledi fossils, we have constrained the depositional age of Homo naledi to a period between 236 ka and 335 ka.” ↩

2. 3b.

   Section Introduction, paragraph 2:  “Dates acquired via U-Th and ESR techniques were obtained using a double blind approach for each technique to ensure robust, reproducible results, with each laboratory using their own analytical and computational approach.” ↩

3. 3c.

   Section Results, U-Th dating of flowstones:  “Flowstone samples that overlie sub-unit 3b, which contains the H. naledi fossils, yield age estimates that fall within four distinct time periods: ~242 ka (RS18 = 242 ± 5 ka [JCU] and 242.9 ± 6.6 ka [UoM]) for Flowstone 1c; 88–106 ka (RS1, RS8, RS13-17); 50 ka (RS6); and 24–32 ka (RS10, RS19-21) for Flowstone Group 2 deposits.  The results for RS18 provide a minimum age for the H. naledi fossils in this part of the cave.”  The still-growing stalagmite RS11 gave 9.05 ± 0.06 ka at JCU and 9.95 ± 0.06 ka at UoM;  the oldest flowstone samples gave about 478 to 502 ka. ↩ ↩ ↩

4. 3d.

   Section Results, U-Th dating of flowstones:  “An actively forming (i.e., dripping) stalagmite of Flowstone Group 3 (RS11) on top of an older base of Flowstone Group 2 returned a younger age of 9–10 ka (RS11 = 9.05 ± 0.06 [JCU] and 9.95 ± 0.06 ka [UoM]).”  Section Methods, Flowstone samples for U-Th dating:  “RS11 was taken from the top 3 mm of this white flowstone (Figure 3f).” ↩

5. 3e.

   Table 1:  The summary table of uranium-thorium ages from both laboratories for the seventeen chamber samples and one surface sample, with each sample's flowstone group and the unit beneath it.  It labels RS13 "rim to RS18" and RS18 "core to RS13". ↩

6. 3f.

   Section Discussion, U-Th results:  “This is certainly the case here, where samples analysed in duplicate in independent laboratories (JCU and UoM) returned identical results within analytical uncertainties (Tables 1, 2 and 3).” ↩

7. 3g.

   Section Methods, Flowstone samples for U-Th dating:  “RS13 and RS18 are two samples taken from the same stalactite developed along the lip of an erosional remnant of Flowstone 1c near the entrance into the Dinaledi Chamber (Figure 1b).  In this location, Flowstone 1c covers the erosional remains of a mud clast breccia containing a long bone consistent with the H. naledi assemblage (Figure 3g), and interpreted as Unit 3.  The stalactite connects to part of the speleothem layers that cover the bone.”  “The sample has been affected by recrystallization resulting in the formation of radiating acicular crystals of calcite that grow from the core outward.”  The stalactite is 53 mm from core to rim:  an 8 mm core, a central zone of about 23 mm and an outer zone of about 22 mm.  RS18 was cut from a 3 mm horizon near the base of the central zone and RS13 from the outermost part of the outer zone, so the two are up to about 45 mm apart.  The rim gave about 88 ka and the inner sample about 242 ka. ↩ ↩

8. 3h.

   Section Discussion, U-Th results:  “In particular, the effects of possible post-depositional U uptake, which would result in apparent ages that are younger than the true age, can be assessed with textural analyses (e.g., Pickering et al., 2010), and the use of initial ^234U/238U ratios (Tables 2 and 3; Kronfeld et al., 1994).  Most of the analysed flowstones display similar initial ^234U/238U ratios (1.8 to 2.4), with two notable exceptions in samples RS18 (243 ± 7 ka) and RS5 (290 ± 6 ka) that record ^234U/238U ratios of 3 to 4.  These are two of the oldest samples analysed, and both display evidence for recrystallization and secondary dissolution.  Considering that the groundwater reservoir in the CoH has high (i.e., >7) initial ^234U/238U ratios (Kronfeld et al., 1994) it is likely that the elevated ^234U/238U ratios in samples RS5 and RS18 are due to U uptake during interaction with groundwater after flowstone deposition.  In this case, these two age results should be viewed as minimum age estimates for the flowstones.” ↩ ↩ ↩

9. 3i.

   Section Results, US-ESR dating:  “Together these results provide an age range of 139–335 ka for the H. naledi remains, although dating of flowstone encasing H. naledi bones helps to better constrain this range”. ↩

10. 3j.

    Section Discussion, Age estimates for H. naledi and implications for hominin evolution:  “The maximum age limit of 335 ka for the H. naledi fossils relies on 80% Rn loss throughout the burial history of the fossils and is probably an over-estimate.” ↩ ↩

11. 3k.

    Section Discussion, Age estimates for H. naledi and implications for hominin evolution:  “Considering the observed Rn loss in the cave sediments, the maximum age estimate is considered to be closer to the true age.” ↩

12. 3l.

    Section Discussion, Age estimates for H. naledi and implications for hominin evolution:  “The lower age limit of 139 ka must be disregarded and shifted to ~200 ka considering a U-Th minimum age estimate for parts of enamel on tooth sample 1810 (Table 5).  This minimum age limit can be constrained further to 236 ka based on U-Th age estimates for Flowstone 1c (242.0 ± 5.0 ka; 242.9 ± 6.6 ka; Table 1), which directly covers fossil material of H. naledi”. ↩ ↩

13. 3m.

    Section Results, OSL dating:  “The MAM calculations for the three samples yield maximum age estimates for the sediments of 231 ± 41 ka (OSL3), 241 ± 37 ka (OSL4), and 353 ± 61 ka (OSL5). … Note that if a Central Age Model (CAM) is applied to the OSL data, results are significantly older at 560 ± 102 ka (OSL3), 546 ± 79 ka (OSL4), and 849 ± 132 ka (OSL5), however, this model is considered unrealistic within a cave environment”. ↩ ↩

14. 3n.

    Section Results, OSL dating:  “Optically stimulated luminescence (OSL) dating of three samples of sediment from Unit 1 in the Dinaledi Chamber (samples OSL3 and OSL4 from sub-unit 1b, and sample OSL5 from sub-unit 1a; Figure 5) was performed at the University of the Witwatersrand (Wits).”  “Sample OSL5 was obtained from muddy sediment of sub-unit 1a, and yields an older age than the covering flowstones (RS5 and RS20).” ↩

15. 3o.

    Section Discussion, An updated stratigraphy for the Dinaledi Chamber:  “The oldest, phase A layer at the base of Flowstone 1a records reversed magnetic polarity indicating that it formed before 780 ka (Singer, 2014).”  Flowstone 1a overlies Unit 2, not the hominin-bearing sub-unit 3b. ↩

16. 3p.

    Section Discussion, Reliability of the age estimates:  “U-series analysis on carbonates, ^14C analysis of bone and palaeomagnetic analyses of flowstones … are well established dating techniques requiring few, if any, à priori assumptions.  In contrast, ESR and OSL results are strongly dependent on model assumptions for the environmental conditions that affected the locations from which the samples were taken.” ↩

17. 3q.

    Section Discussion, US-ESR and OSL results:  “To assure that all US-ESR results obtained by the different laboratories can be compared in an objective manner, we standardized the à priori model assumptions (Table 6), that is, the same analytical results for sediment chemistry, back ground radiation, water content, radon-loss and cosmogenic radiation, needed to calculate the environmental dose rate, were used by both laboratories.” ↩

18. 3r.

    Section Results, US-ESR dating:  “In obtaining the ages, each laboratory carried out independent sample preparation, and ESR and U-series analyses of the fossil teeth.  Estimates for the environmental dose rates used in the age calculations were standardized for both laboratories (Table 6) in order to produce comparable results”.  Section Discussion, US-ESR and OSL results:  “Therefore, any differences in age estimates relate to the measured equivalent dose (DE) and laboratory methodologies, and are not the result of model assumptions.” ↩

19. 3s.

    Table 7:  Maximum-age scenario, ages in thousands of years:  tooth 1810 gave 284 ± 51 at Southern Cross University and 267 ± 68 at the Spanish laboratory;  tooth 1788 gave 247 ± 42 and 211 ± 28;  tooth 1767 gave 104 ± 29.  Internal dose rates in the same scenario, in micrograys a year:  1,142 for tooth 1767, 190 and 47 for 1788, 323 and 176 for 1810.  The table also lists each tooth's sediment beta, gamma-and-cosmic and total dose rates. ↩ ↩ ↩

20. 3t.

    Section Discussion, U-Th results:  “Since Th is immobile, each U uptake event that affects the tooth will shift pre-existing U-Th systematics to portray a younger age (Grün et al., 2014).  The variable U-Th disequilibrium ages are a clear indication that U uptake events took place, and provide a minimum age estimate for the true age of the teeth.” ↩

21. 3u.

    Section Author response, opening statement:  “For ESR we have now standardized the modelling input parameters for the ESR models.  Originally the results provided by the two labs varied significantly, largely because each lab had made different à priori model assumptions (as a result of this being a double blind experiment), which would have been hard to spot by any non-specialist.  To allow for more objective comparisons of the two different data sets, we have now based all ESR modelling on mutually agreed to in-put parameters for the environmental dose rates”. ↩ ↩

22. 3v.

    Section Decision letter, Reviewer #5:  “The external dose rate is as much as 80-90% of the total dose rate for the hominin teeth.”  “On the whole, there seems little leeway for significant changes in external dose rate.”  Written of the first submission.  The reviewer recommended only minor revision. ↩ ↩

23. 3w.

    Section Discussion, US-ESR and OSL results:  “their ages as obtained by SCU vary by a factor of >2 (scenario 1: 104 ± 29 vs 247 ± 42 ka; scenario 2: 87 ± 22 ka vs 194 ± 34 ka; Table 7).  The main difference between the two samples is that the internal dose rate of sample 1767 is ~20 times higher (Table 7), due to the high U concentration in the enamel (~2.5 ppm). … Given these factors, we do not trust the reliability of the age results for sample 1767 and have excluded this tooth from the final age estimates for the fossils.” ↩

24. 3x.

    Section Decision letter, Reviewer #4:  “It seems like interpretations are being changed to fit the dates as opposed to being based on the primary evidence/material (sedimentology, fossils) themselves.”  “The most important one is that sample RS18 is said to overly Unit 3 (hominin-bearing) in the text, but Unit 2 in the Table.  This is a key date they use for anchoring the hominin fossils.  Wondering if the change wasn't made in the table because they altered their unit assignments only after the dates were produced.”  “Perhaps it was Unit 2 until they decided to change it Unit 3 because of the age (i.e., changing based on age, not sedimentology).” ↩

25. 3y.

    Section Author response, Reviewer #4:  “In other words, the reassignment of lithological units to their appropriate chronostratigraphic position was firstly based on the new age results.”  “The reviewer is correct in assuming that we altered the unit assignment after the dates came in as is usual in the stratigraphic allocations of sediments to units when chronostratigraphic constraints are acquired (as explained above).  The real reason for the mix-up, however, is that an older version of the table was sent in by accident.”  “Corrected.  Also, getting an age to establish stratigraphy is a normal process in stratigraphy.” ↩ ↩ ↩

26. 3z.

    Section Discussion, An updated stratigraphy for the Dinaledi Chamber:  “Flowstone 1c returns an age of ~243 ka (Table 1), suggesting that the sediments below Flowstones 1b-e are significantly younger than Unit 2 sediments below Flowstone 1a … Therefore, we reinterpret the H. naledi-bearing sediments below Flowstones 1b-e as part of Unit 3 (sub-unit 3b)”. ↩

27. 3aa.

    Section Results, Radiocarbon dating:  “Three weathered bone fragments of H. naledi were analysed via radiocarbon dating at Beta Analytic Inc. (Florida, USA).  Analyses indicated that no collagen was present in any of the samples and that the bone appeared possibly cremated.  This was investigated with a bone carbonate extraction technique.  Tests did not support cremation and indicated that extensive secondary CaCO3 replacement had occurred, providing ages of 33.0 ± 0.2 ka and 35.50 ± 0.16 ka for two of the fragments.  We interpret these ages to relate to late calcite precipitation in the bones that may reflect a wet period in the cave.”  The three fragments were a tibia shaft, a femur shaft and a hand or foot bone shaft, collected from the surface of Unit 3 near the excavation pit. ↩ ↩ ↩ ↩ ↩

28. 3ab.

    Section Dating the H. naledi fossils:  “At the time these dating tests were done, it was already known from U-Th and OSL tests that the H. naledi fossils would be too old to be dated by ^14C.  Nevertheless, analyses were carried out as part of the due diligence process, and the results of these tests are presented here.  Following this initial work, no further radiocarbon studies were carried out.” ↩

29. 3ac.

    Section Dating the H. naledi fossils:  “Tests with radiocarbon (^14C) dating were undertaken through a commercial facility (Beta Analytic Inc. in Florida), to ensure a fast turn-around time for results.”  Section Methods, Methodology for radiocarbon dating:  “Two bone fragments collected along the floor of the Dinaledi Chamber near the top of sub-unit 3b were sent to Beta Analytic Inc. in Miami, Florida.”  “Samples were then ground to a powder and pre-treated with 1N acetic acid for 24 hr, rinsed, dried and weighed.”  “Ages are calculated using BetaCal 3.17 provided by Beta Analytic following procedures outlined in Bronk Ramsey (2009) and using the SHCAL13 database (Hogg et al., 2013).  Dates are reported as radiocarbon years before present (‘BP’ with ‘present’ taken as AD 1950).” ↩ ↩

30. 3ad.

    Section Decision letter, Reviewer #2:  “Why wasn't radiocarbon dating pursued in the same manner, using established research labs rather than a commercial lab?  Why no details of the procedures: e.g., was ultrafiltration attempted?” ↩

31. 3ae.

    Section Author response, Reviewer #2:  “As explained in the text carbon dating was done “as due diligence to obtain an indication if carbon dating should be further pursued”.”  “The initial results from the commercial lab indicated that carbon dating was not going to work.  Subsequent U-Th and ESR work made it clear that carbon dating should not be further pursued, and attempting blind dates at research labs would be pointless as far as the purpose of this study is concerned, and we did not want to unnecessarily impose on people’s time and expenses.  We are only reporting the carbon dates here for completeness sake, and the fact that it corroborates flowstone formation around 30ka.” ↩

32. 3af.

    Section Decision letter, second round:  “I have no problem with the authors saying those 3 particular fossils have a best fit of 236-335 ka, but does anything preclude the other hominid specimens from being associated with older or younger parts of upper unit 3 with the potential to span approximately 90ka (min of above RS1/15 above U3) to 414 ka (max of OSL5)?” ↩

33. 3ag.

    Section Decision letter:  “The reviewers were in agreement that the paper’s base is strong, with separate, generally consistent results obtained by the two excellent labs.”  The reviewing editor's summary of the first round of five reviews. ↩

34. 3ah.

    Section Results, US-ESR dating:  “Combined US-ESR ages for the baboon tooth (sample 1841) determined by SCU using scenario 1 and 2 conditions are 723 ± 181 ka and 635 ± 148 ka respectively.”  “The age results provide an upper age limit for the deposition of the H. naledi bearing layer”.  Section Methods, Tooth samples for ESR dating:  “The specimen was recovered from a sediment sample taken at a depth of 55–60 cm below the original ground surface of the cave floor near the base of the sondage dug in the centre of the excavation pit (Figures 1b, 2d and 4).  This tooth occurs in sub-unit 3a, ~40 cm below the stratigraphically lowest occurrence of partly articulated remains of H. naledi, and represents the only non-hominin macrofossil recovered from Unit 3.”  Table 4:  The mean uranium-thorium age of the tooth's enamel is 115.6 ± 3.8 ka. ↩

Count and comparison for this article, from Table 1 of Dirks et al. 2017.³  The seventeen chamber samples come from twelve deposits, because five pairs share one:  RS1 and RS15, blind duplicates;  RS11 and RS21, top and base;  RS13 and RS18, rim and inner part of one stalactite;  RS16 and RS17, top and base;  RS22 and RS23, top and base.  Eleven samples have an age from both laboratories.  In thousands of years, James Cook University first and the University of Melbourne second:  RS19 24.7 ± 0.2 and 24.53 ± 0.43;  RS11 9.05 ± 0.06 and 9.946 ± 0.063;  RS21 28.4 ± 0.4 and 28.62 ± 0.29;  RS20 30.4 ± 0.2 and 32.12 ± 0.38;  RS6 49.8 ± 0.3 and 50.82 ± 0.43;  RS15 92.6 ± 1.0 and 91.40 ± 0.65;  RS8 95.0 ± 1.0 and 96.29 ± 0.69;  RS14 100.1 ± 1.2 and 96.20 ± 0.36;  RS17 102.6 ± 0.8 and 98.6 ± 1.4;  RS16 104.0 ± 1.9 and 99.1 ± 1.4;  RS18 242 ± 5 and 242.9 ± 6.6.  The differences run from 0.4 percent at RS18 to 9.9 percent at RS11.  Adding each pair's two stated two-sigma errors in quadrature, six pairs differ by more than their combined error, by factors of 2 to 10:  RS11, RS20, RS6, RS14, RS17 and RS16.  Two sit at its edge, RS15 and RS8.  Three are well inside it:  RS19, RS21 and RS18. ↩ ↩ ↩

Arithmetic for this article, from Table 7 of Dirks et al. 2017.³  The dose a tooth received from outside itself is the sediment beta dose plus the gamma and cosmic dose, and both laboratories were given the same sediment chemistry, water content, radon loss and cosmic rate from which those are computed.  As a share of the total dose rate in the maximum-age scenario:  tooth 1788, (105 + 549)/935 = 70 percent at Southern Cross University and (86 + 549)/754 = 84 percent at the Spanish laboratory;  tooth 1810, (95 + 549)/1042 = 62 percent and (86 + 549)/870 = 73 percent.  In the minimum-age scenario:  (134 + 739)/1191 = 73 percent and (111 + 739)/978 = 87 percent for tooth 1788;  (126 + 739)/1287 = 67 percent and (112 + 739)/1102 = 77 percent for tooth 1810.  The reviewer's "as much as 80-90%" was written of the first submission, whose table is not public. ↩

Dirks, Paul H. G. M. et al.  “Geological and taphonomic context for the new hominin species Homo naledi from the Dinaledi Chamber, South Africa.”  eLife 4:e09561.  2015.  The excavating team's first account of the chamber, its access route, its sediments and the bone surfaces, and the origin of the "deliberate body disposal" reading.  It placed the hominin bones in two of its three stratigraphic units, Units 2 and 3;  the 2017 dating paper moved the loose, bone-bearing sediment under Flowstones 1b to 1e from Unit 2 to Unit 3, which put all the hominin bones in one sub-unit.  Mirror:  PMC

1. 6a.

   Section Abstract:  “Preliminary evidence is consistent with deliberate body disposal in a single location, by a hominin species other than Homo sapiens, at an as-yet unknown date.” ↩

2. 6b.

   Section Results, Stratigraphic units in the Dinaledi Chamber, Unit 2:  “In contrast, erosion remnants of Unit 2 that are preserved underneath aprons of Flowstones 1b–e (Figure 4C), are mostly unconsolidated and have a rubbly appearance.”  “This includes the shafts of a juvenile hominin ulna and radius contained in a collapsed portion of unconsolidated Unit 2 sediment derived from below Flowstone 1b, which are consistent with the remains of H. naledi.” ↩

3. 6c.

   Section Results, Flowstones in the Dinaledi Chamber:  “These formed at separate times, and help demarcate stratigraphic units.  Each type of flowstone is described below starting with the oldest.”  “Deposits of Flowstone 2 partly cover remains of Flowstone 1a–e, and portions of the floor of the cave.”  “Deposits of Flowstone 3 are currently active flowstone formations in the Dinaledi Chamber”. ↩

Cherkinsky, Alexander.  “Can We Get a Good Radiocarbon Age from "Bad Bone"?  Determining the Reliability of Radiocarbon Age from Bioapatite.”  Radiocarbon 51(2):647–655.  2009.  A methods paper from the University of Georgia's Center for Applied Isotope Studies on dating the carbonate fraction of bone and tooth when little or no collagen survives, tested against paired collagen and charcoal dates from a few hundred to more than 40,000 radiocarbon years.

1. 7a.

   Page 649, section Chemical Cleaning:  “The carbonates in fossil bone may be contaminated by secondary carbonates, precipitated in the process of burial either as pore-filling cements or as bicarbonates absorbed to the surface of crystals.  To remove these diagenetic carbon compounds, the bone is soaked overnight in 1N acetic acid.” ↩

2. 7b.

   Page 653, section Conclusion:  “In the case of samples derived from carbonate environments, the possibility of isotope exchange is increased, especially in changing conditions of wet and dry seasons.  Thus, reactions of dissolution and precipitation occur and affect the carbon isotope composition by rejuvenation of the ^14C age.  On the other hand, if old carbonate material is present it could be leached from the deposits and the ^14C age of the samples may seem older as a result of exchange with old, “dead” carbonates.” ↩

Arithmetic for this article.  A conventional radiocarbon age t is defined from the measured fraction F of modern carbon-14 by t = −8033 ln F, so F = exp(−t/8033).²³  For 33,000 years F = 1.64 percent;  for 35,500 years F = 1.20 percent;  for 24,000 years F = 5.04 percent;  for 30,000 years F = 2.39 percent;  for 32,000 years F = 1.86 percent.  The paper's methods say that dates are reported as radiocarbon years before present and also describe a calibration step.³  The two ages are read here as conventional ages.  If they are calibrated ages instead, the conventional ages are a few thousand years younger, the fractions somewhat higher and the shares below somewhat lower.  Old bone plus later calcite.  Bone carbonate older than about 50,000 years holds no measurable carbon-14, so a mixture reading 1.20 to 1.64 percent must contain a share of later calcite equal to that reading divided by the calcite's own fraction:  24 to 33 percent if the calcite reads 24,000 radiocarbon years, 50 to 69 percent at 30,000, and 65 to 88 percent at 32,000.  The range of 24 to 32 thousand years is the uranium-thorium age of the chamber's late flowstones, in calendar years.³  A radiocarbon age on the same calcite would be somewhat younger than its calendar age and somewhat older for any carbon it took from dissolved dolomite, which is dead.  The two corrections pull opposite ways, so the shares are a guide and not a measurement.  If the contamination were modern carbon at 100 percent, only 1.2 to 1.6 percent of it would be needed, which is the reading Rupe and Sanford's page 227 attributes to the paper and the paper does not make.²⁰  A young bone.  Real decay runs on the 5,730 year half-life, so carbon 4,500 years old keeps exp(−4500/8267) = 58 percent of what it started with.  No young-earth model claims the air then held today's ratio.  For scale only:  if it had, a 4,500 year old bone would need 97 to 98 percent of its carbonate replaced by dead carbon to read 1.20 to 1.64 percent.  On the RATE model, in which the ratio was still rising from a low value after the Flood,¹⁰ the same bone reads as measured with no contamination if it formed at 1.20/0.58 = 2.1 to 1.64/0.58 = 2.8 percent of today's ratio.  That starting ratio is this article's arithmetic, not a figure any young-earth source has published for these bones. ↩ ↩ ↩

Thomas, Brian.  “Cherry-Picked Age for Key Evolutionary Fossil.”  Institute for Creation Research, Creation Science Update.  Jun 8, 2017.  ICR's answer to the 2017 dating paper, published a month after it.

1. 9a.

   “Dating methods should reveal their reliability by independently giving very similar ages for the same sample and its surroundings.  But these six results landed all over the place, leaving an 800,000 year gap between the youngest and oldest dates.”  “Last, C-14 results for associated bones ranged from 33,000 to about 35,500 carbon years.”  The second sentence is the youngest result the article lists;  the oldest is the 849,000 year figure. ↩ ↩

2. 9b.

   “U-Th on the flowstone FS1b showed an age of about 290,000 uranium years, but OSL (CAM) results ranged from 546,000 to 560,000 years.  OSL (MAM) on flowstone FS1a showed 353,000 years, but OSL (CAM) gave approximately 849,000!”  “Will the real flowstone age please stand up?” ↩

3. 9c.

   “They did not even explain why they rejected the U-Th result from three different Homo naledi teeth”.  “At least they offered some reasoning when they cited contamination from calcite precipitation as affecting the C-14 results.  But what direct observation of contamination led them to this speculation?  They gave none.” ↩ ↩ ↩ ↩

4. 9d.

   “Anatomically modern human remains already occur in Middle Pleistocene sediments, which in a biblical timeline were deposited during the post-Flood Ice Age”. ↩

Baumgardner, John R.  “^14C Evidence for a Recent Global Flood and a Young Earth.”  Radioisotopes and the Age of the Earth, volume II, chapter 8, 587–630.  Institute for Creation Research and Creation Research Society.  2005.  The radiocarbon chapter of the final report of the RATE project, by a geophysicist who worked at Los Alamos National Laboratory.  It is the fullest statement of the young-earth model of carbon-14:  a biosphere before the Flood with far more carbon and a far lower carbon-14 ratio than today's.

1. 10a.

   Page 617:  “With a date for the Biblical Flood derived from the Masoretic Hebrew text of only about 4500 years ago, which is less than the ^14C half-life, one would expect that ^14C in plants and animals buried in this cataclysm to be detectable today.” ↩

2. 10b.

   Page 619:  “implies a pre-Flood ^14C/C ratio of about 0.2 pMC.  Again, we emphasize this estimate is very soft.”  “it is necessary for the ^14C/C ratio to have increased dramatically and rapidly, by a factor on the order of 500, to reach its present value after the cataclysm.  The means by which this could have occurred has long been a difficulty for the young-earth Creation/global Flood framework.”  pMC is percent of the modern carbon-14 ratio. ↩ ↩ ↩

Ambler, Marc, and Joel Tay.  “What to make of Homo naledi?”  Creation Ministries International, creation.com.  Sep 13, 2015.  The 2015 article in which CMI publicly offered to fund radiocarbon dating of the bones, with an update of 12 December 2025 by Joel Tay on the 2017 radiocarbon result.

1. 11a.

   Section Update, 12 December 2025:  “Naledi bones contain radiocarbon, so they cannot possibly be as old as evolutionists claim.  Furthermore, modern radiocarbon laboratories go to great lengths to account for contamination.  For example, these laboratories don’t just test for ^14C and ^12C, they also test for ^13C.  This allows them to account for modern contamination in their samples.”  “This yielded a radiocarbon date of 33,000—35,000 years old, one tenth of their accepted date, and one hundredth of their original date for H. naledi.”  “The dates were deemed to be too young, and so they were rejected, with contamination suggested as the reason.” ↩ ↩ ↩

2. 11b.

   Section Update, 12 December 2025:  “A baboon tooth just a few centimeters under H. naledi gave an ESR date of 721,000 years.  This same tooth gave a date of 115,000 years old using U-Th.”  “You would think that these two methods should agree, but they didn’t, so both were rejected.”  “A flowstone (one of several types of cave formation) a few centimeters away gave a date of 88,000 and 242,000 years.  However, using U-Th, they got an age that ranged from 9,000–500,000 years!  Comparing all the results from the oldest to youngest, there was a difference of 840,000 years!” ↩ ↩

3. 11c.

   Section Update, 12 December 2025:  “Homo Naledi was initially believed to be 2.5–2.8 million years old (2015).  This was before the researchers carried out any radiometric tests.” ↩

Robbins, Jessie L. et al.  “Providing context to the Homo naledi fossils:  Constraints from flowstones on the age of sediment deposits in Rising Star Cave, South Africa.”  Chemical Geology 567:120108.  Apr 20, 2021.  The excavating team's second dating paper:  29 new flowstone dates from the chambers along the route to the Dinaledi Chamber, and the source of the 241 thousand year floor.  The quotations here are from its abstract.  A 2022 erratum in the same journal replaced its Table 2.  Mirror:  Researchonline.jcu.edu.au

1. 12a.

   Section Abstract:  “The new ages further constrain the minimum age of H. naledi to ~241 ka.  Thus, H. naledi entered the cave between 241 ka and 335 ka, during a glacial period, at which time clastic sediments inside the cave were undergoing erosion.” ↩

2. 12b.

   Section Abstract:  “H. naledi would probably have entered the cave through an access point in the roof of the Postbox Chamber and made its way along a SW trending fracture towards the Dragon's Back and Dinaledi Chambers.” ↩

Berger, Lee R. et al.  “Evidence for deliberate burial of the dead by Homo naledi.”  eLife 12:RP89106.  Sep 1, 2025.  The version of record of the burial paper, about 50,000 words with appendices, revised after the 2023 reviews.  Reviewed preprint 12 July 2023;  revised 28 March 2025;  version of record 1 September 2025.  Places are its section and appendix headings.

1. 13a.

   Section Appendix 2.1, Entrances to the cave system:  “Present evidence shows that some H. naledi remains entered the Dinaledi Subsystem between 335,000 and 241,000 years ago (Dirks et al., 2017; Robbins et al., 2021).  No geochronological estimate yet exists for the Lesedi Chamber material, and the Dinaledi Subsystem results do not exclude the possibility that some individuals may represent a broader time range.” ↩ ↩

2. 13b.

   Section Introduction, The Rising Star cave system and Homo naledi localities:  “A comprehensive uranium-thorium (U/Th) dating of flowstone units in the subsystem was carried out, resulting in a chronology for flowstone formation; the most informative sample was a flowstone unit directly encasing bone.  The U/Th age of 244±3 ka for this flowstone (RS18, RS68) is inferred to be a minimum age for the osteological specimen embedded within it, which has been suggested as the minimum age constraint for H. naledi skeletal material in the subsystem (Dirks et al., 2017; Robbins et al., 2021).” ↩

Madupe, Palesa P. et al.  “Proteomic analysis of dental enamel from 20 Homo naledi individuals shows no male markers.”  Cell 189(14):4415–4424.e11.  Jun 24, 2026.  Enamel proteins recovered from 23 teeth of at least 20 naledi individuals from several parts of the cave system, including the Lesedi skeleton.  The author list ends with John Hawks, Lee Berger and Enrico Cappellini, so it is the excavating team's own result.  Mirror:  PMC

1. 14a.

   Section Introduction:  “Some of these remains have been dated to 335–236 ka … although the estimated range for some specimens may be a wider interval (±70 ka).” ↩

2. 14b.

   Section Results, paragraph 1:  “The extent of racemization of free and total hydrolyzable amino acids (FAA and THAA, respectively) indicates that the enamel from all four H. naledi specimens behaved as a closed system retaining endogenous peptides”.  “The lower level of amino acid degradation, compared with the published samples from the nearby fossil hominin site of Swartkrans, is consistent with their younger geological age.”  Degradation was assessed from amino-acid composition, the free fraction and the ratio of right-handed to left-handed forms, on the enamel of four teeth.  The enamel racemisation method the paper follows is that of Dickinson, Lister and Penkman 2019. ↩

Hawks, John et al.  “New fossil remains of Homo naledi from the Lesedi Chamber, South Africa.”  eLife 6:e24232.  2017.  Describes the second naledi site, 131 hominin specimens from at least three individuals, including the partial skeleton with a nearly complete skull that was nicknamed "Neo", and its access route.  Mirror:  PMC

1. 15a.

   Section eLife digest:  “the material from the Lesedi Chamber is undated”. ↩

2. 15b.

   Section Results, Location of the Lesedi Chamber:  “There are currently four access routes from the surface to the Lesedi Chamber.  The most accessible of these currently follows an 86 m downward-sloping path with several narrow passages and short climbs, but only one squeeze and no significant crawls.  This has been the main access route for excavators.  The other three routes are each substantially more challenging.” ↩

Wise, Kurt P.  “Paleontological Note on Homo naledi.”  Journal of Creation Theology and Science Series B: Life Sciences 6:9–13.  2016.  The most careful young-earth reading of the 2015 taphonomy paper, by a Harvard-trained palaeontologist.  Written before any date existed.  Mirror:  Archive.org

1. 16a.

   Page 13:  “Although H. naledi has not yet been dated, it is found in a cave system that dates from the uppermost Pliocene and younger (Dirks et al. 2015). … All hominins, then, date from centuries after the Flood and most – and probably all – date from post-Babel times (Wise 1994).” ↩

Clarey, Timothy L.  “Disposal of Homo naledi in a possible deathtrap or mass mortality scenario.”  Journal of Creation 31(2):61–70.  2017.  The Institute for Creation Research geologist's model:  the bones were floated into the chambers by post-Flood flash floods, and naledi was an ape.

1. 17a.

   Page 67:  “Both of these bone chamber deposits likely occurred in the Ice Age, a time when the climate was likely experiencing more rainfall from the effects of the recent global Flood.  It is therefore possible that flash-flooding of the Dragon’s Back Chamber transported either previously deceased or H. naledi taking refuge in the cave entrance, ultimately dismembering the bodies and floating the partial remains to the Dinaledi and Lesedi Chambers of the cave system”. ↩

Hardy, Chris, and Robert Carter.  “The biblical minimum and maximum age of the earth.”  Journal of Creation 28(2):89–96.  2014.  A young-earth paper in Creation Ministries International's journal that works out the earliest and latest dates the biblical numbers allow for creation and the Flood, across the Masoretic, Samaritan and Septuagint texts and a long or short sojourn in Egypt.

1. 18a.

   Page 96:  “The Flood probably occurred between 2600 bc and 2300 bc, but certainly between 3386 bc and 2256 bc (table 5).” ↩ ↩

Arithmetic for this article.  Hardy and Carter's Flood dates¹⁸ in years before 2026:  3386 BC is 5,411 years ago, 2600 BC is 4,625, 2300 BC is 4,325 and 2256 BC is 4,281.  Dividing 33,000 by these gives 6.1, 7.1, 7.6 and 7.7.  Dividing 241,000 by them gives 45, 52, 56 and 56.  A young-earth model puts the bones after the Flood, so each ratio is a minimum.  The 33,000 is a radiocarbon age and the 241,000 a uranium-thorium age;  a young-earth reading takes neither as a calendar date, and the ratios are given to show scale. ↩

Rupe, Christopher, and John Sanford.  Contested Bones.  FMS Publications.  2017.  A young-earth survey of the hominin fossils.  Chapter 10 treats naledi as an inbred human population and the chamber as a ritual burial place;  a section of chapter 12 answers the 2017 date.  Page numbers are those of the 2017 first edition;  the 2019 printing is paginated differently.

1. 20a.

   Page 227:  “Naledi's age was tested using carbon-14 analysis. … Nevertheless, carbon-14 was surprisingly detected, suggesting an age for Naledi of about 30,000 years old.  However, this “anomalously” young age was promptly rejected by Dirks et al., who claimed that the samples must have been contaminated with modern carbon.  No further samples were subjected to carbon-14 analysis.”  Page 303:  “Carbon-14 dating was used to date the fossil material, yet those results gave an age for Naledi that was too young (33,000 and 35,500 years old for two of the dated bones), and so these dates were rejected on the basis of presumed contamination.”  The book's footnote 140 to the second passage gives the paper's own reason, quoting its words on extensive secondary calcium carbonate replacement. ↩ ↩ ↩

2. 20b.

   Page 302:  “At the end of their analysis they had to reinterpret the stratigraphy to agree with ages obtained from the dating methods.  This introduces a dilemma: does the stratigraphy give meaning to the age estimates (as they stated in the paper) or do the age estimates give meaning to the stratigraphy (as their reevaluation assumed)?  Expect the stratigraphy of the cave and the age of Naledi to be revised in upcoming papers”. ↩

3. 20c.

   Page 303:  “For instance, the baboon tooth found just centimeters below the Naledi remains gave an ESR age of 721,000 years, yet its U-Th age was 115,000 years.  Obviously both ages cannot be correct.”  “All of the three Naledi teeth that were U-Th dated were rejected, apparently because the age estimates were too young (43,000-146,000 years).”  Page 303, footnote 143:  “Dirks et al. insist that the U-Th dates for the teeth are “minimum age estimates” and not the depositional age of the fossils.  It was assumed that the young ages represented uranium uptake events during wet periods in the chamber.” ↩ ↩

4. 20d.

   Pages 303–304:  “Different parts of the same flowstone sample, separated by just a few centimeters, gave widely differing ages (88,000 and 242,000 years).” ↩

5. 20e.

   Page 304:  “Indeed, the U-Th method yielded a very wide scatter of ages (9,000 to 500,000 years)—a clear indicator that this widely-used dating method is subject to open system behavior, and is therefore unreliable.” ↩ ↩

6. 20f.

   Page 304:  “The many dating methods employed by Berger et al. gave an incredible spectrum of ages (an 840,000 year gap between the youngest and oldest dates). … It seems quite clear that the true age of Naledi is still unknown.” ↩

Line, Peter.  “Den of ape-men or chambers of the sickly?  An update of Homo naledi.”  Creation Ministries International, creation.com.  May 23, 2017.  Line's response to the 2017 dating and Lesedi papers.

1. 21a.

   “I do not accept the above-mentioned age dates, as radiometric dating is based on unverifiable and problematic assumptions.”  “The much younger radiocarbon dates are explained away by the statement: “We interpret these ages to relate to late calcite precipitation in the bones that may reflect a wet period in the cave.”” ↩ ↩

O'Micks, J.  “Further Evidence That Homo naledi Is Not a Member of the Human Holobaramin Based on Measurements of Vertebrae and Ribs.”  Answers Research Journal 10:103–113.  2017.  The fourth of O'Micks's five papers arguing that naledi is not human, on the vertebrae and ribs, with a closing section on the 2017 date.

1. 22a.

   Page 111:  “A recent dating of the H. naledi fossils, flowstones, and sediments from the DiNaledi chamber have put the depositional evolutionary age of H. naledi at between 236–335 ka. … Such a young date for H. naledi obviously contradicts the overarching evolutionary narrative that H. naledi is basal to the genus Homo, preceding all other species from within that genus.” ↩

Stuiver, Minze, and Henry A. Polach.  “Discussion:  Reporting of ^14C Data.”  Radiocarbon 19(3):355–363.  1977.  The paper that fixed how radiocarbon laboratories calculate and report an age, including the definition of a conventional radiocarbon age.

1. 23a.

   Page 356, section 3, Radiocarbon age calculation:  “are called conventional radiocarbon ages (years BP).  This term implies:  A. the use of the 5568 yr half-life (mean life 8033 y)”. ↩

2. 23b.

   Page 357:  “A conventional radiocarbon age, as defined in section 3, does take into account ^13C fractionation but not differences in ^14C specific activity of reservoirs which arise from effects other than isotopic fractionation.” ↩

The Associated Press.  “Introducing ‘Homo Naledi’, Our Ancient Human Relative.”  The Quint.  Sep 10, 2015.  The wire report of the announcement of Homo naledi, as carried by an Indian news site.  Rupe and Sanford and Joel Tay both cite this copy for the 2.5 to 2.8 million year figure.

1. 24a.

   “Lee Berger, a professor at the University of the Witwatersrand in Johannesburg who led the work, said naledi’s anatomy suggest that it arose at or near the root of the Homo group, which would make the species some 2.5 million to 2.8 million years old.  The discovered bones themselves may be younger, he said.” ↩