Neutron Capture Enhances Dose and Reduces Cancer Cell Viability in and out of Beam During Helium and Carbon Ion Therapy.

PURPOSE: Neutron capture enhanced particle therapy (NCEPT) is a proposed augmentation of charged particle therapy that exploits thermal neutrons generated internally, within the treatment volume via nuclear fragmentation, to deliver a biochemically targeted radiation dose to cancer cells. This work is the first experimental demonstration of NCEPT, performed using both carbon and helium ion beams with 2 different targeted neutron capture agents (NCAs). METHODS AND MATERIALS: Human glioblastoma cells (T98G) were irradiated by carbon and helium ion beams in the presence of NCAs [10B]-BPA and [157Gd]-DOTA-TPP. Cells were positioned within a polymethyl methacrylate phantom either laterally adjacent to or within a 100 × 100 × 60 mm spread out Bragg peak (SOBP). The effect of NCAs and location relative to the SOBP on the cells was measured by cell growth and survival assays in 6 independent experiments. Neutron fluence within the phantom was characterized by quantifying the neutron activation of gold foil. RESULTS: Cells placed inside the treatment volume reached 10% survival by 2 Gy of carbon or 2 to 3 Gy of helium in the presence of NCAs compared with 5 Gy of carbon and 7 Gy of helium with no NCA. Cells placed adjacent to the treatment volume showed a dose-dependent decrease in cell growth when treated with NCAs, reaching 10% survival by 6 Gy of carbon or helium (to the treatment volume), compared with no detectable effect on cells without NCA. The mean thermal neutron fluence at the center of the SOBP was approximately 2.2 × 109 n/cm2/Gy (relative biological effectiveness) for the carbon beam and 5.8 × 109 n/cm2/Gy (relative biological effectiveness) for the helium beam and gradually decreased in all directions. CONCLUSIONS: The addition of NCAs to cancer cells during carbon and helium beam irradiation has a measurable effect on cell survival and growth in vitro. Through the capture of internally generated neutrons, NCEPT introduces the concept of a biochemically targeted radiation dose to charged particle therapy. NCEPT enables the established pharmaceuticals and concepts of neutron capture therapy to be applied to a wider range of deeply situated and diffuse tumors, by targeting this dose to microinfiltrates and cells outside of defined treatment regions. These results also demonstrate the potential for NCEPT to provide an increased dose to tumor tissue within the treatment volume, with a reduction in radiation doses to off-target tissue.

The demise of the giant ape Gigantopithecus blacki.

The largest ever primate and one of the largest of the southeast Asian megafauna, Gigantopithecus blacki1, persisted in China from about 2.0 million years until the late middle Pleistocene when it became extinct2-4. Its demise is enigmatic considering that it was one of the few Asian great apes to go extinct in the last 2.6 million years, whereas others, including orangutan, survived until the present5. The cause of the disappearance of G. blacki remains unresolved but could shed light on primate resilience and the fate of megafauna in this region6. Here we applied three multidisciplinary analyses-timing, past environments and behaviour-to 22 caves in southern China. We used 157 radiometric ages from six dating techniques to establish a timeline for the demise of G. blacki. We show that from 2.3 million years ago the environment was a mosaic of forests and grasses, providing ideal conditions for thriving G. blacki populations. However, just before and during the extinction window between 295,000 and 215,000 years ago there was enhanced environmental variability from increased seasonality, which caused changes in plant communities and an increase in open forest environments. Although its close relative Pongo weidenreichi managed to adapt its dietary preferences and behaviour to this variability, G. blacki showed signs of chronic stress and dwindling populations. Ultimately its struggle to adapt led to the extinction of the greatest primate to ever inhabit the Earth.

Reconstructing Pleistocene Australian herbivore megafauna diet using calcium and strontium isotopes.

Isotopes in fossil tooth enamel provide robust tools for reconstructing food webs, which have been understudied in Australian megafauna. To delineate the isotopic composition of primary consumers and understand dietary behaviour at the base of the food web, we investigate calcium (Ca) and strontium (Sr) isotope compositions of Pleistocene marsupial herbivores from Wellington Caves and Bingara (New South Wales, Australia). Sr isotopes suggest small home ranges across giant and smaller marsupial herbivores. Ca isotopes in Pleistocene marsupial herbivores cover the same range as those in modern wombats and placental herbivores. Early forming teeth are depleted in heavy Ca isotopes compared to late-forming teeth of a given individual, suggesting a weaning signal. Distinct Ca compositions between taxa can be interpreted as dietary niches. Some niches conform to previous dietary reconstructions of taxa, while others provide new insights into niche differentiation across Australian herbivores. Combined with the small roaming ranges suggested by Sr isotopes, the Ca isotope niche diversity suggests rich ecosystems, supporting a diversity of taxa with various diets in a small area.

Early presence of Homo sapiens in Southeast Asia by 86-68 kyr at Tam Pà Ling, Northern Laos.

The timing of the first arrival of Homo sapiens in East Asia from Africa and the degree to which they interbred with or replaced local archaic populations is controversial. Previous discoveries from Tam Pà Ling cave (Laos) identified H. sapiens in Southeast Asia by at least 46 kyr. We report on a recently discovered frontal bone (TPL 6) and tibial fragment (TPL 7) found in the deepest layers of TPL. Bayesian modeling of luminescence dating of sediments and U-series and combined U-series-ESR dating of mammalian teeth reveals a depositional sequence spanning ~86 kyr. TPL 6 confirms the presence of H. sapiens by 70 ± 3 kyr, and TPL 7 extends this range to 77 ± 9 kyr, supporting an early dispersal of H. sapiens into Southeast Asia. Geometric morphometric analyses of TPL 6 suggest descent from a gracile immigrant population rather than evolution from or admixture with local archaic populations.

Calcium isotopes as a biomarker for vascular calcification in chronic kidney disease.

Calcium balance is abnormal in adults with chronic kidney disease (CKD) and is associated with the development of vascular calcification. It is currently not routine to screen for vascular calcification in CKD patients. In this cross-sectional study, we investigate whether the ratio of naturally occurring calcium (Ca) isotopes, 44Ca and 42Ca, in serum could be used as a noninvasive marker of vascular calcification in CKD. We recruited 78 participants from a tertiary hospital renal center: 28 controls, 9 subjects with mild-moderate CKD, 22 undertaking dialysis and 19 who received a kidney transplant. For each participant, systolic blood pressure, ankle brachial index, pulse wave velocity, and estimated glomerular filtration rate were measured, along with serum markers. Calcium concentrations and isotope ratios were measured in urine and serum. While we found no significant association between urine Ca isotope composition (noted δ44/42Ca) between the different groups, δ44/42Ca values in serum were significantly different between healthy controls, subjects with mild-moderate CKD and those undertaking dialysis (P < 0.01). Receiver operative characteristic curve analysis shows that the diagnostic utility of serum δ44/42Ca for detecting medial artery calcification is very good (AUC = 0.818, sensitivity 81.8% and specificity 77.3%, P < 0.01), and performs better than existing biomarkers. Although our results will need to be verified in prospective studies across different institutions, serum δ44/42Ca has the potential to be used as an early screening test for vascular calcification.

Thresholds for the presence of glacial megafauna in central Europe during the last 60,000 years.

Lake sediment records from Holzmaar and the infilled maar of Auel (Eifel, Germany) are used to reconstruct landscape changes and megafauna abundances. Our data document a forested landscape from 60,000 to 48,000 yr b2k and a stepwise vegetation change towards a glacial desert after 26,000 yr b2k. The Eifel landscape was continuously inhabited from 48,000 to 9000 yr b2k by large mammals, documented by the presence of spores of coprophilous fungi from Sordaria and Sporormiella fungi that grow on fecal remains of the megafauna. Megafauna reached higher numbers during cold stadial climates but was present also during the warmer interstadials. Highest abundance was at 56,500/48,500/38,500/33,000/27,000/21,000/16,200/14,000 yr b2k, i.e. under different climate regimes. Some of these dates were associated with clear human presence, which indicates that megafauna was not overkilled by humans. In contrast, human presence could quite likely have been stimulated by the abundant food supply. Megafauna presence decreased significantly when tree abundance increased during interstadials. The Megafauna disappeared finally at 11,400 yr b2k with the development of the early Holocene forest cover, which appears to be the most important threshold for megafauna presence.

Response to Comment on "A global environmental crisis 42,000 years ago".

Our study on the exact timing and the potential climatic, environmental, and evolutionary consequences of the Laschamps Geomagnetic Excursion has generated the hypothesis that geomagnetism represents an unrecognized driver in environmental and evolutionary change. It is important for this hypothesis to be tested with new data, and encouragingly, none of the studies presented by Picin et al. undermine our model.

Response to Comment on "A global environmental crisis 42,000 years ago".

Our paper about the impacts of the Laschamps Geomagnetic Excursion 42,000 years ago has provoked considerable scientific and public interest, particularly in the so-called Adams Event associated with the initial transition of the magnetic poles. Although we welcome the opportunity to discuss our new ideas, Hawks' assertions of misrepresentation are especially disappointing given his limited examination of the material.

A global environmental crisis 42,000 years ago.

Geological archives record multiple reversals of Earth's magnetic poles, but the global impacts of these events, if any, remain unclear. Uncertain radiocarbon calibration has limited investigation of the potential effects of the last major magnetic inversion, known as the Laschamps Excursion [41 to 42 thousand years ago (ka)]. We use ancient New Zealand kauri trees (Agathis australis) to develop a detailed record of atmospheric radiocarbon levels across the Laschamps Excursion. We precisely characterize the geomagnetic reversal and perform global chemistry-climate modeling and detailed radiocarbon dating of paleoenvironmental records to investigate impacts. We find that geomagnetic field minima ~42 ka, in combination with Grand Solar Minima, caused substantial changes in atmospheric ozone concentration and circulation, driving synchronous global climate shifts that caused major environmental changes, extinction events, and transformations in the archaeological record.

Determination of magnesium isotopic ratios of biological reference materials via multi-collector inductively coupled plasma mass spectrometry.

RATIONALE: Despite a wide range of potential applications, magnesium (Mg) isotope composition has been so far sparsely measured in reference materials with a biological matrix, which is important for the quality control of the results. We describe a method enabling the chemical separation of Mg in geological and biological materials and the determination of its stable isotope composition. METHODS: Different geological (BHVO-1, BHVO-2, BCR-1, and IAPSO) and biological (SRM-1577c, BCR-383, BCR380R, ERM-CE464, DORM-2, DORM-4, TORT-3, and FBS) reference materials were used to test the performance of a new sample preparation procedure for Mg isotopic analysis. The procedure consisted of a simple three-stage elution method to separate Mg from the matrix. Mg isotopic analyses were performed in two different laboratories and with three different multi-collector inductively coupled plasma mass spectrometry instruments. RESULTS: The biological reference materials show a wide range of δ26 Mg values (relative to DSM3 standard), spanning over 2‰, from 0.52 ± 0.29‰ (2SD, n = 7) in bovine liver (SRM-1577c) to -1.45 ± 0.20‰ (2SD, n = 5) in tuna fish (ERM-CE464), with an external precision of 0.03‰ (2SD, n = 85). CONCLUSIONS: This study indicates that isotopic measurements of Mg in biological reference materials show good performance, with the results being within the accepted range. We confirmed that δ26 Mg values in liver are the most positive of all biological materials reported so far.

Extinction of eastern Sahul megafauna coincides with sustained environmental deterioration.

Explanations for the Upper Pleistocene extinction of megafauna from Sahul (Australia and New Guinea) remain unresolved. Extinction hypotheses have advanced climate or human-driven scenarios, in spite of over three quarters of Sahul lacking reliable biogeographic or chronologic data. Here we present new megafauna from north-eastern Australia that suffered extinction sometime after 40,100 (±1700) years ago. Megafauna fossils preserved alongside leaves, seeds, pollen and insects, indicate a sclerophyllous forest with heathy understorey that was home to aquatic and terrestrial carnivorous reptiles and megaherbivores, including the world's largest kangaroo. Megafauna species diversity is greater compared to southern sites of similar age, which is contrary to expectations if extinctions followed proposed migration routes for people across Sahul. Our results do not support rapid or synchronous human-mediated continental-wide extinction, or the proposed timing of peak extinction events. Instead, megafauna extinctions coincide with regionally staggered spatio-temporal deterioration in hydroclimate coupled with sustained environmental change.

Elemental signatures of Australopithecus africanus teeth reveal seasonal dietary stress.

Reconstructing the detailed dietary behaviour of extinct hominins is challenging1-particularly for a species such as Australopithecus africanus, which has a highly variable dental morphology that suggests a broad diet2,3. The dietary responses of extinct hominins to seasonal fluctuations in food availability are poorly understood, and nursing behaviours even less so; most of the direct information currently available has been obtained from high-resolution trace-element geochemical analysis of Homo sapiens (both modern and fossil), Homo neanderthalensis4 and living apes5. Here we apply high-resolution trace-element analysis to two A. africanus specimens from Sterkfontein Member 4 (South Africa), dated to 2.6-2.1 million years ago. Elemental signals indicate that A. africanus infants predominantly consumed breast milk for the first year after birth. A cyclical elemental pattern observed following the nursing sequence-comparable to the seasonal dietary signal that is seen in contemporary wild primates and other mammals-indicates irregular food availability. These results are supported by isotopic evidence for a geographical range that was dominated by nutritionally depauperate areas. Cyclical accumulation of lithium in A. africanus teeth also corroborates the idea that their range was characterized by fluctuating resources, and that they possessed physiological adaptations to this instability. This study provides insights into the dietary cycles and ecological behaviours of A. africanus in response to food availability, including the potential cyclical resurgence of milk intake during times of nutritional challenge (as observed in modern wild orangutans5). The geochemical findings for these teeth reinforce the unique place of A. africanus in the fossil record, and indicate dietary stress in specimens that date to shortly before the extinction of Australopithecus in South Africa about two million years ago.

Assessment of metal concentrations in the SOD1G93A mouse model of amyotrophic lateral sclerosis and its potential role in muscular denervation, with particular focus on muscle tissue.

BACKGROUND: Amyotrophic lateral sclerosis (ALS) is among the most common of the motor neuron diseases, and arguably the most devastating. During the course of this fatal neurodegenerative disorder, motor neurons undergo progressive degeneration. The currently best-understood animal models of ALS are based on the over-expression of mutant isoforms of Cu/Zn superoxide dismutase 1 (SOD1); these indicate that there is a perturbation in metal homeostasis with disease progression. Copper metabolism in particular is affected in the central nervous system (CNS) and muscle tissue. METHODS: This present study assessed previously published and newly gathered concentrations of transition metals (Cu, Zn, Fe and Se) in CNS (brain and spinal cord) and non-CNS (liver, intestine, heart and muscle) tissues from transgenic mice over-expressing the G93A mutant SOD1 isoform (SOD1G93A), transgenic mice over-expressing wildtype SOD1 (SOD1WT) and non-transgenic controls. RESULTS: Cu accumulates in non-CNS tissues at pre-symptomatic stages in SOD1G93A tissues. This accumulation represents a potentially pathological feature that cannot solely be explained by the over-expression of mSOD1. As a result of the lack of Cu uptake into the CNS there may be a deficiency of Cu for the over-expressed mutant SOD1 in these tissues. Elevated Cu concentrations in muscle tissue also preceded the onset of symptoms and were found to be pathological and not be the result of SOD1 over-expression. CONCLUSIONS: It is hypothesized that the observed Cu accumulations may represent a pathologic feature of ALS, which may actively contribute to axonal retraction leading to muscular denervation, and possibly significantly contributing to disease pathology. Therefore, it is proposed that the toxic-gain-of-function and dying-back hypotheses to explain the molecular drivers of ALS may not be separate, individual processes; rather our data suggests that they are parallel processes.

Impact of climate change and human activity on soil landscapes over the past 12,300 years.

Soils are key to ecosystems and human societies, and their critical importance requires a better understanding of how they evolve through time. However, identifying the role of natural climate change versus human activity (e.g. agriculture) on soil evolution is difficult. Here we show that for most of the past 12,300 years soil erosion and development were impacted differently by natural climate variability, as recorded by sediments deposited in Lake Dojran (Macedonia/Greece): short-lived ( < 1,000 years) climatic shifts had no effect on soil development but impacted soil erosion. This decoupling disappeared between 3,500 and 3,100 years ago, when the sedimentary record suggests an unprecedented erosion event associated with the development of agriculture in the region. Our results show unambiguously how differently soils evolved under natural climate variability (between 12,300 and 3,500 years ago) and later in response to intensifying human impact. The transition from natural to anthropogenic landscape started just before, or at, the onset of the Greek 'Dark Ages' (~3,200 cal yr BP). This could represent the earliest recorded sign of a negative feedback between civilization and environmental impact, where the development of agriculture impacted soil resources, which in turn resulted in a slowdown of civilization expansion.

Quaternary vertebrate faunas from Sumba, Indonesia: implications for Wallacean biogeography and evolution.

Historical patterns of diversity, biogeography and faunal turnover remain poorly understood for Wallacea, the biologically and geologically complex island region between the Asian and Australian continental shelves. A distinctive Quaternary vertebrate fauna containing the small-bodied hominin Homo floresiensis, pygmy Stegodon proboscideans, varanids and giant murids has been described from Flores, but Quaternary faunas are poorly known from most other Lesser Sunda Islands. We report the discovery of extensive new fossil vertebrate collections from Pleistocene and Holocene deposits on Sumba, a large Wallacean island situated less than 50 km south of Flores. A fossil assemblage recovered from a Pleistocene deposit at Lewapaku in the interior highlands of Sumba, which may be close to 1 million years old, contains a series of skeletal elements of a very small Stegodon referable to S. sumbaensis, a tooth attributable to Varanus komodoensis, and fragmentary remains of unidentified giant murids. Holocene cave deposits at Mahaniwa dated to approximately 2000-3500 BP yielded extensive material of two new genera of endemic large-bodied murids, as well as fossils of an extinct frugivorous varanid. This new baseline for reconstructing Wallacean faunal histories reveals that Sumba's Quaternary vertebrate fauna, although phylogenetically distinctive, was comparable in diversity and composition to the Quaternary fauna of Flores, suggesting that similar assemblages may have characterized Quaternary terrestrial ecosystems on many or all of the larger Lesser Sunda Islands.

From direct to indirect lithium targets: a comprehensive review of omics data.

Metal ions are critical to a wide range of biological processes. Among them, lithium (Li) has been recognised for its benefit as a treatment for bipolar disorder (BD). However, we are yet to grasp the extent of its role in biological processes, despite its molecular targets having been extensively studied. Here we review a wide range of transcriptomic, proteomic and metabolomic studies in order to obtain a full picture of Li effects at various levels. Multifarious patterns of Li-regulated genes, proteins and metabolites are identified. Some of these patterns are explained as the outcomes of individual Li targets. For instance, Li inhibition of GSK-3 has a wide range of effects: axis development in embryos; cell and tissue differentiation, in particular neurogenesis and osteogenesis; or control of apoptosis. This results in neuroprotection and an attenuation of cognitive deficits. Lithium plays an important role in mitochondrial function, which it improves via its role in phospholipid metabolism and inositol depletion. This is also seen in metabolomics, where its role in the mitochondrial respiratory chain influences energy production and oxidative stress. Lithium also affects the proteins involved in the processing of APP, thus highlighting a possible involvement in Alzheimer's disease. Finally, Li also impacts lipid homeostasis, with studies showing that environmental exposure can impact lipid transport and prostaglandin synthesis. It is seldom possible to establish a causal relationship between Li targets at the molecular level and the resulting effects at the system level. For example, Li effects on adenylate cyclase regulation are not easily linked to any omic pattern despite the importance of the adenylate pathway. Nevertheless, refining our knowledge on the cellular functions of individual Li targets would improve our understanding and interpretation of omics data. This review demonstrates that Li is key to a wide range of processes at all levels, from neuroprotection to oxidative stress and energy production. A corollary of this work is the need for an increased awareness of environmental issues related to Li industrial wastes, in particular considering the widespread use of this metal in our modern society.

The age of Homo naledi and associated sediments in the Rising Star Cave, South Africa.

New ages for flowstone, sediments and fossil bones from the Dinaledi Chamber are presented. We combined optically stimulated luminescence dating of sediments with U-Th and palaeomagnetic analyses of flowstones to establish that all sediments containing Homo naledi fossils can be allocated to a single stratigraphic entity (sub-unit 3b), interpreted to be deposited between 236 ka and 414 ka. This result has been confirmed independently by dating three H. naledi teeth with combined U-series and electron spin resonance (US-ESR) dating. Two dating scenarios for the fossils were tested by varying the assumed levels of 222Rn loss in the encasing sediments: a maximum age scenario provides an average age for the two least altered fossil teeth of 253 +82/-70 ka, whilst a minimum age scenario yields an average age of 200 +70/-61 ka. We consider the maximum age scenario to more closely reflect conditions in the cave, and therefore, the true age of the fossils. 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. These age results demonstrate that a morphologically primitive hominin, Homo naledi, survived into the later parts of the Pleistocene in Africa, and indicate a much younger age for the Homo naledi fossils than have previously been hypothesized based on their morphology.

Longitudinal assessment of metal concentrations and copper isotope ratios in the G93A SOD1 mouse model of amyotrophic lateral sclerosis.

Amyotrophic lateral sclerosis (ALS) is a motor neuron disease, which involves progressive motor neuron degeneration in the central nervous system (CNS). The G93A SOD1 mouse model simulates one of the most common causes of familial ALS through the overexpression of a mutated form of the human gene encoding copper/zinc superoxide dismutase (SOD1). Transition metals, particularly Cu and Zn, have been shown to behave abnormally in the disease context and have been hypothesized to contribute to and potentially trigger the disease. In this study, concentrations of Cu, Zn and Fe, as well as Cu isotope ratios were assessed in keystone tissues of ALS, including the brain, spinal cord, muscle and whole blood, from transgenic mutant SOD1G93A mice and non-transgenic controls. While no consistent Cu isotope signal was found to be related to the disease state, concentrations of Cu, Zn and Fe were significantly elevated in muscle tissue of the transgenic mice, even at pre-symptomatic time points. In brain and muscle tissue, in both animal groups, a time-dependent Cu isotope signal was observed. We hypothesize that the early and significant elevation in metal concentration in muscle tissue from SOD1 transgenic mice could facilitate the development of ALS, without affecting the overall signal from well-buffered CNS tissues. Ageing may be recorded isotopically as a shift from a neonatal Cu pool as inherited from the mother, through dietary Cu and recycling processes.

Using (1)(0)Be cosmogenic isotopes to estimate erosion rates and landscape changes during the Plio-Pleistocene in the Cradle of Humankind, South Africa.

Concentrations of cosmogenic (10)Be, measured in quartz from chert and river sediment around the Cradle of Humankind (CoH), are used to determine basin-averaged erosion rates and estimate incision rates for local river valleys. This study focusses on the catchment area that hosts Malapa cave with Australopithecus sediba, in order to compare regional versus localized erosion rates, and better constrain the timing of cave formation and fossil entrapment. Basin-averaged erosion rates for six sub-catchments draining the CoH show a narrow range (3.00 ± 0.28 to 4.15 ± 0.37 m/Mega-annum [Ma]; ±1σ) regardless of catchment size or underlying geology; e.g. the sub-catchment with Malapa Cave (3 km(2)) underlain by dolomite erodes at the same rate (3.30 ± 0.30 m/Ma) as the upper Skeerpoort River catchment (87 km(2)) underlain by shale, chert and conglomerate (3.23 ± 0.30 m/Ma). Likewise, the Skeerpoort River catchment (147 km(2)) draining the northern CoH erodes at a rate (3.00 ± 0.28 m/Ma) similar to the Bloubank-Crocodile River catchment (627 km(2)) that drains the southern CoH (at 3.62 ± 0.33 to 4.15 ± 0.37 m/Ma). Dolomite- and siliciclastic-dominated catchments erode at similar rates, consistent with physical weathering as the rate controlling process, and a relatively dry climate in more recent times. Erosion resistant chert dykes along the Grootvleispruit River below Malapa yield an incision rate of ∼8 m/Ma at steady-state erosion rates for chert of 0.86 ± 0.54 m/Ma. Results provide better palaeo-depth estimates for Malapa Cave of 7-16 m at the time of deposition of A. sediba. Low basin-averaged erosion rates and concave river profiles indicate that the landscape across the CoH is old, and eroding slowly; i.e. the physical character of the landscape changed little in the last 3-4 Ma, and dolomite was exposed on surface probably well into the Miocene. The apparent absence of early Pliocene- or Miocene-aged cave deposits and fossils in the CoH suggests that caves only started forming from 4 Ma onwards. Therefore, whilst the landscape in the CoH is old, cavities are a relatively young phenomenon, thus controlling the maximum age of fossils that can potentially be preserved in caves in the CoH.

Revised stratigraphy and chronology for Homo floresiensis at Liang Bua in Indonesia.

Homo floresiensis, a primitive hominin species discovered in Late Pleistocene sediments at Liang Bua (Flores, Indonesia), has generated wide interest and scientific debate. A major reason this taxon is controversial is because the H. floresiensis-bearing deposits, which include associated stone artefacts and remains of other extinct endemic fauna, were dated to between about 95 and 12 thousand calendar years (kyr) ago. These ages suggested that H. floresiensis survived until long after modern humans reached Australia by ~50 kyr ago. Here we report new stratigraphic and chronological evidence from Liang Bua that does not support the ages inferred previously for the H. floresiensis holotype (LB1), ~18 thousand calibrated radiocarbon years before present (kyr cal. BP), or the time of last appearance of this species (about 17 or 13-11 kyr cal. BP). Instead, the skeletal remains of H. floresiensis and the deposits containing them are dated to between about 100 and 60 kyr ago, whereas stone artefacts attributable to this species range from about 190 to 50 kyr in age. Whether H. floresiensis survived after 50 kyr ago--potentially encountering modern humans on Flores or other hominins dispersing through southeast Asia, such as Denisovans--is an open question.