We consider one misconception of those who currently reject the general validity of radiocarbon (14C) age determinations older than, at most, 10,000 BP. There is an allegation that the presence of 14C reported by accelerator mass spectrometry (AMS) laboratories in their measurements of 14C infinite age (>100,000 years) organics used to define background levels, support their point of view. This article has been written for a general audience, primarily for those who have questions about the validity of these arguments. However, they may not be familiar with the literature relevant to providing a clear response to the claims of these individuals. We conclude that, in our view, of all of the possible explanations for the reports of the presence of 14C in these background samples, the least probable explanation has been advanced by those rejecting the validity of the 14C time scale in excess of, at most, 10,000 BP.

The Early Bronze Age (EBA) is associated with technological and cultural changes that may suggest the onset of a new culture. The question usually posed is whether the spread of the EBA culture is a matter of contemporary evolutionary practices or a matter of migration of peoples. We contribute to this discussion by tracing the appearance and spread of the EBA in the Aegean using an absolute time-frame provided by more than 200 radiocarbon (14C) dates from 25 different Aegean sites. These have been compiled and statistically treated, individually, and in geographical groups to allow temporal and spatial comparisons. A new model is constructed for the first time for northern Greece. The dates are compared between various settlements and areas in each of the traditional cultural divisions EBA I, EBA II, and EBA III and possible subdivisions. The statistical treatment and comparisons indicate that the EBA appeared slightly earlier, around 3300 BC, in northern Greece than in southern Greece, and the Cycladic Islands and also lasted longer in some areas in northern Greece, ending at around 1900 BC.

Organic carbon (OC) radiocarbon (14C) signatures in marine surface sediments are highly variable and the causes of this heterogeneity remain ambiguous. Here, we present results from a detailed 14C-based investigation of an Arabian Sea sediment, including measurements on organic matter (OM) in bulk sediment, specific grain size fractions, and OC decomposition products from ramped-pyrolysis-oxidation (RPO). Our results show that 14C ages of OM increase with increasing grain size, suggesting that grain size is an important factor controlling the 14C heterogeneity in marine sediments. Analysis of RPO decomposition products from different grain size fractions reveals an overall increase in age of corresponding thermal fractions from finer to coarser fractions. We suggest that hydrodynamic properties of sediment grains exert the important control on the 14C age distribution of OM among grain size fractions. We propose a conceptual model to account for this dimensionality in 14C variability that invokes two predominant modes of OM preservation within different grain size fractions of Arabian Sea sediment: finer (<63 µm) fractions are influenced by OM-mineral grain aggregation processes, giving rise to relatively uniform 14C ages, whereas OM preserved in coarser (>63 µm) fractions includes materials encapsulated within microfossils and/or entrained fossil (14C-depleted) OC hosted in detrital mineral grains. Our findings highlight the value of RPO for assessment of 14C age variability in sedimentary OC, and for assessing mechanisms of OM preservation in aquatic sediments.

Inland water bodies contain significant amounts of carbon in the form of dissolved inorganic carbon (DIC) derived from a mixture of modern atmospheric and pre-aged sources, which needs to be considered in radiocarbon-based dating and natural isotope tracer studies. While reservoir effects in hardwater lakes are generally considered to be constant through time, a comparison of recent and historical DI14C data from 2013 and 1969 for Lake Constance reveals that this is not a valid assumption. We hypothesize that changes in atmospheric carbon contributions to lake water DIC have taken place due to anthropogenically forced eutrophication in the 20th century. A return to more oligotrophic conditions in the lake led to reoxygenation and enhanced terrigenous organic matter remineralization, contributing to lake water DIC. Such comparisons using DI14C measurements from different points in time enable nonlinear changes in lake water DIC source and signature to be disentangled from concurrent anthropogenically induced changes in atmospheric 14C. In the future, coeval changes in lake dynamics due to climate change are expected to further perturb these balances. Depending on the scenario, Lake Constance DI14C is projected to decrease from the 2013 measured value of 0.856 Fm to 0.54–0.62 Fm by the end of the century.

The “governor’s residency” at Tel ‘Eton was destroyed in the late 8th century BCE in an Assyrian military campaign. While the numerous finds enable a detailed reconstruction of life on the eve of the destruction, this elite house was cleaned continuously, and since no floor raisings were identified, little was known of the building’s period of use. Radiocarbon (14C) samples taken from within a foundation deposit and from the floor make-up, however, indicate that the earliest phase of the residency was built in the late 11th–10th century BCE. This has bearings on the date in which social complexity evolved in Judah, on the debate regarding the historicity of the kingdom of David and Solomon, and it also provides the earliest date for the use of ashlar stones in Judah. Finally, the long life of the “governor’s residency” exemplifies a little addressed phenomenon—the old-house effect—in which buildings and settlements existed for a few centuries, but only left significant remains from their last phase. The earlier phases are hardly represented in the finds, barely studied, and rarely published. We suggest that the old-house effect influences archaeological interpretations world-wide, and is also responsible for recent attempts to down-date social complexity in Judah.

This article is a critical review of published data from the earliest evidence of pressure knapped microblade technology from various regions in Northeast Asia (Siberia, Korea, China, Mongolia, Japan, Sakhalin, and Russian Far East), including discussions not only on published dates, but also on published artifacts (drawings and photos) relating to these assemblages. The issue concerning the geographical and chronological origin of microblade technology in Northeast Asia remains a widely debated concern, not only as new data emerge, but also due to researchers having different definitions of the term “microblade” and “microblade core”. In this case, by microblade technology, I refer to the systematic production of microblades using the pressure knapping technique. I therefore review the data in light of this defining feature and conclude that, based on the present state of research, pressure knapping microblade technology probably emerged in the Far East (China, Korea, or Japan) around 30,000–25,000 cal BP, in spite of most authors considering that microblade technology emerged in southern Siberia 40,000–35,000 years ago. In the discussion section, I argue about the potential role of obsidian in the emergence of pressure knapped microblade technology.

During the Last Glacial Maximum (LGM) the Tagliamento glacier delivered large amounts of sediment to the Cormor alluvial megafan on the southern Alpine foreland basin. To build a chronology of Late Pleistocene glacier fluctuations and assess the timing of the transition from interstadial to glacial conditions, we have performed radiocarbon (14C) dating on peat and macrofossil samples obtained from a drilling core from the distal Cormor megafan. Our chronology records fluvial and glaciofluvial aggradation from the end of MIS 3 until the end of the LGM. It shows a rapid transmission of signals of environmental change along the Cormor megafan, so that changes in the activity of the Tagliamento glacier directly affect glaciofluvial sedimentation. Our data demonstrate that the intrinsic heterogeneity of peat is most critical for the reliability and reproducibility of the obtained 14C ages. Macrofossil subsamples give evidence for significant mixing of organic components of different ages within single peat samples. Sample heterogeneity is also underlined by the results obtained from testing of different laboratory precleaning methods. Our results suggest that a rigorous ABA pretreatment is sufficient for peat cleaning. In contrast, the chemically stronger ABOX methods appear to rapidly degrade the peat, particularly destroying older organic components.

Lime lumps and bulk mortars show different 14C contamination when analyzed in several CO2 fractions isolated from the effervescence of an ongoing hydrolysis reaction. Age profiles of both materials are therefore highly complementary and together they can provide a reliable date. Furthermore, they can also reveal the complexity of the radiocarbon (14C) distribution within the mortar and thus prevent over-interpretation of the data. The lime lump versus bulk mortar dating data presented here has been collected over 22 years, with only a small fraction of the results so far published internationally. Since there has been an increasing interest in mortar dating over recent years with a special focus on lime lumps, and since many laboratories have just begun mortar dating experiments, we wish to present some of the extensive data that already exist. Previously published data from 15 lime lumps (including 34 14C measurements from sequential dissolution) and 43 new 14C measurements from 17 lime lumps are presented here. The samples are from medieval Finland and Sweden, classical Rome and medieval Italy, and the Roman Jerash (Gerasa), Jordan.

Radiocarbon dates from recent excavations of a range of Angkorian Khmer (~9th–14th CE) stoneware kiln complexes provide a new and independent perspective on the timing and geography of Khmer ceramic production. These data demonstrate a clear two-phase sequence. The first, in the late 9th to late 12th centuries CE, marks a period of intensive production located both to the east of Angkor and to the south at Cheung Ek, south of Phnom Penh. A second shorter phase of production occurred in the late 13th to late 14th CE at more distant provincial settings following the collapse of the Angkorian state.

Because the 14C calibration curves IntCal and SHCal are based on data from temperate latitudes, it remains unclear which curve is more suitable for archaeological and paleoenvironmental records from tropical South America. A review of climate dynamics reveals a significant influx of Northern Hemisphere air masses and moisture over a substantial part of the continent during the South American Summer Monsoon (SASM). Areas affected by the SASM receive unknown amounts of input from both hemispheres, where an argument could be made for either curve. Until localized tree-ring data can resolve this, we suggest using a mixed calibration curve, which accounts for inputs from both hemispheres, as a third calibration option. We present a calibration example from a crucial period of environmental and cultural change in the southern Lake Titicaca. Given our current lack of data on past ∆14C variation in South America, our calibrations and chronologies will likely change in the future. We hope this paper spurs new research into this topic and encourages researchers to make an informed and explicit choice of which curve to use, which is particularly relevant in research on past human–environmental relationships.

We evaluated the spatial heterogeneity of historical carbon accumulation rates in a forested, ombrotrophic bog in Minnesota to aid understanding of responses to an ongoing decade-long warming manipulation. Eighteen peat cores indicated that the bog has been accumulating carbon for over 11,000 years, to yield 176±40 kg C m−2 to 225±58 cm of peat depth. Estimated peat basal ages ranged from 5100 to 11,100 cal BP. The long-term apparent rate of carbon accumulation over the entire peat profile was 22±2 g C m−2 yr−1. Plot location within the study area did not affect carbon accumulation rates, but estimated basal ages were younger in profiles from plots closer to the bog lagg and farther from the bog outlet. In addition, carbon accumulation varied considerably over time. Early Holocene net carbon accumulation rates were 30±6 g C m−2 yr−1. Around 3300 calendar BP, net carbon accumulation rates dropped to 15±8 g C m−2 yr−1 until the last century when net accumulation rates increased again to 74±57 g C m−2 yr−1. During this period of low accumulation, regional droughts may have lowered the water table, allowing for enhanced aerobic decomposition and making the bog more susceptible to fire. These results suggest that experimental warming treatments, as well as a future warmer climate may reduce net carbon accumulation in peat in this and other southern boreal peatlands. Furthermore, our we caution against historical interpretations extrapolated from one or a few peat cores.

This paper examines the marine reservoir effect for Tomales Bay, a 25.5-km-long tidal estuary along the northern coast of California. We determined the regional ∆R through radiocarbon (14C) measurements of pre-1950 shells from a museum collection as well as archaeologically recovered shell samples from a historical railroad grade of known construction date. These results are compared against four sets of paired shell and bone samples from two local archaeological sites. Our results indicate little spatial variation along the inner bay, but the proposed ∆R value is lower than those previously reported for nearby areas along the Pacific Coast. We also note potential variability in regional ∆R of approximately 200 14C years for the late Holocene, and comparison with an older paired bone and shell sample points toward more significant temporal variation earlier in time.

A large collection of maize macro-specimens has been gathered from archaeological sites across the American continent, but only a few have been directly dated by accelerator mass spectrometry (AMS). We recently conducted two new excavations in several rock shelters of Tehuacán valley (San Marcos, Coxcatlán, and Purrón) and uncovered 132 non-manipulated macro-specimens of maize suitable for morphological and paleogenomic analysis, including many complete cobs, stalks, internodes, and leaves. Direct AMS dates for 43 samples found in San Marcos or Coxcatlán confirm the previously reported chronologies for these sites. By contrast, a cob found in Purrón was dated to 3060±30 before present (3360–3180 cal BP) (2σ), demonstrating that maize was present at that site at least 1500 calendar years earlier than previously expected, and suggesting that other specimens of similar age are still likely to be found in the southeastern region of the Tehuacán valley. A global comparison of macro-specimen chronology across the continent shows that the current archaebotanical record does not yet reflect the chronology of dispersal from central Mexico to northern or southern regions, opening the possibility for finding the missing links in subsequent expeditions within Mexico and Central America.

We applied the high temperature pyrolysis-combustion technique to partition the total soil organic carbon (SOC) into labile and inert carbon pools for accelerator mass spectrometry radiocarbon (AMS 14C) dating and stable carbon isotope (δ13C), SOC, and carbonate carbon (CC) content analyses to examine SOC variability at a Critical Zone Observatory site in Illinois, USA. The AMS 14C dates of labile and inert carbon in the top 1.55 m overlap except in the Bt horizon. Below 1.55 m the labile carbon is younger by 8000–14,800 years. The SOC content decreases from 3.61% to 0.12% and CC content increases from 0% to 19.16% at this depth. Results indicate that SOC production exceeds its loss in the weathering zone causing a continuous turnover of both SOC pools. A small amount of modern SOC infiltrates into deeper sediment below 1.55 m, making the labile carbon pool much younger. Their difference of AMS 14C contents, ΔF14C, reveals 3−5% more modern carbon in the labile SOC pools except in the Bt horizon, further quantifying that <3−5% modern carbon with potential pollutants is translocated into the unweathered sediments. The δ13C reveals the sources for SOC cycling dynamics in both carbon pools at this site.

We implement a Bayesian statistical analysis of the chronology of Canímar Abajo in Cuba in order to estimate two episodes of burial activity and the period of time corresponding to the hiatus between them. We show that by using simple Bayesian modeling, conclusions can easily be reached by the analysis of the marginal posterior distribution of each parameter of the model. However, we also suggest and describe new statistical tools that exploit the joint posterior distribution of collections of dates. These new tools give complementary information regarding the chronology of human activity.

This sixth date list for the prehistoric site of El Mirón Cave (Cantabria, Spain) reports on new age determinations for the earliest and last Solutrean occupations (20.4 and 18.0 14C kyr BP) and for a Lower/Initial Magdalenian level with a possible rock wall (16.75 14C kyr BP). The site has now been dated by 92 radiocarbon (14C) assays. In addition, to help resolve inconsistencies in the 14C chronology of La Riera Cave (Asturias)—the first Paleolithic site in Spain to be extensively 14C-dated back in the 1970s—two AMS assays were done on bones from the Lower and Upper Magdalenian collections (15.1 and 13.5 14C kyr BP).