Search

The author reflects on a study describing the discovery of two new nuclei. He stresses that the results of the study confirmed that several other nuclei do not exist, as they were not observed during the experiment. Further, the outcomes stretched the limits of current particle accelerators, so discovery of the neutron drip line at higher proton numbers will have to wait for the next generation of facilities.

The article addresses the origin of the air-like xenon component using the ratios of two further isotopes. The results from the radiogenic isotopes indicate that the air-crust hybrid component, which is likely to be added to well gases through local contamination during their storage in the continental crust, can account for only about half of the 90 percent atmospheric xenon component revealed by the non-radiogenic xenon isotopes. They have concluded that some air-like xenon in the New Mexico well-gas samples is intrinsic to their mantle source seems robust.

This article informs that the existence or radioactive aluminium and other short-lived nuclides in the early solar system suggests a source of heat for melting planetesimals, and provides a way of deducing time differences between events. It also means that some stellar process must have created significant amounts of aluminium just before the solar system formed. It is further informed that of the objects found inside chondrites, two have particular significance in the early history of the solar system: calcium aluminium refractory inclusions (CAIs) and chondrules. CAIs are the earliest object yet identified that bear clear isotopic evidence of having formed inside the solar system.

Presents evidence for the presence of ancient lithospheric mantle in a plume source. Variations in isotopic compositions due to long-term differences in the concentrations of trace elements in mantle crustal reservoirs; Rhenium-osmium isotope system that provides a complementary view of lithospheric recycling.

Investigates the birth of the Solar System. Experiments on the selection of meteorites; Calculation of core-formation ages based on isotope data; Assumption that millimeter-sized particles of calcium and aluminum silicates found inside some meteorites are the oldest objects in the Solar System.

Reports the plan of nuclear physicists to build nuclear facilities in the U.S. Priority of build the Rare Isotope Accelerator facility; Endorsement of the strategic plan by the Nuclear Science Advisory Committee; Claim of the research on the importance of knowledge on isotopes.

Shows that cocaine originating from different geographic regions in South America can be identified by its isotope-ratio signature. How the distinct carbon and nitrogen isotope-ratio combinations allow the country of origin to be determined; Use of bivariate mean and standard deviation parameters; Environmental basis for regional variation in coca-leaf and cocaine stable isotopes.

Discusses the use of oxygen-isotope patterns found in sulfate rocks in the Namib Desert and volcanic ash-beds in the western United States to analyze the Earth's prehistoric atmosphere. Use of other light elements in geographic study; Difference between normal oxygen isotopes and those found in sulfate rocks; Suggestions for use of this technique on Mars.

The article focuses on a study conducted by Benjamin Mackey and Michael Lamb at the California Institute of Technology in Pasadena on cosmic rays and rare isotopes generated by them to determine landform dating and predict timing of geological events such as mega floods and rock debris flows.

Earth's mightiest ocean current, the Antarctic Circumpolar Current (ACC), regulates the exchange of heat and carbon between the ocean and the atmosphere, and influences vertical ocean structure, deep-water production and the global distribution of nutrients and chemical tracers. The eastward-flowing ACC occupies a unique circumglobal pathway in the Southern Ocean that was enabled by the tectonic opening of key oceanic gateways during the break-up of Gondwana (for example, by the opening of the Tasmanian Gateway, which connects the Indian and Pacific oceans). Although the ACC is a key component of Earth's present and past climate system, the timing of the appearance of diagnostic features of the ACC (for example, low zonal gradients in water-mass tracer fields) is poorly known and represents a fundamental gap in our understanding of Earth history. Here we show, using geophysically determined positions of continent-ocean boundaries, that the deep Tasmanian Gateway opened 33.5 ± 1.5 million years ago (the errors indicate uncertainty in the boundary positions). Following this opening, sediments from Indian and Pacific cores recorded Pacific-type neodymium isotope ratios, revealing deep westward flow equivalent to the present-day Antarctic Slope Current. We observe onset of the ACC at around 30 million years ago, when Southern Ocean neodymium isotopes record a permanent shift to modern Indian-Atlantic ratios. Our reconstructions of ocean circulation show that massive reorganization and homogenization of Southern Ocean water masses coincided with migration of the northern margin of the Tasmanian Gateway into the mid-latitude westerly wind band, which we reconstruct at 64° S, near to the northern margin. Onset of the ACC about 30 million years ago coincided with major changes in global ocean circulation and probably contributed to the lower atmospheric carbon dioxide levels that appear after this time.

Atmospheric CO2 fluctuations over glacial-interglacial cycles remain a major challenge to our understanding of the carbon cycle and the climate system. Leading hypotheses put forward to explain glacial-interglacial atmospheric CO2 variations invoke changes in deep-ocean carbon storage, probably modulated by processes in the Southern Ocean, where much of the deep ocean is ventilated. A central aspect of such models is that, during deglaciations, an isolated glacial deep-ocean carbon reservoir is reconnected with the atmosphere, driving the atmospheric CO2 rise observed in ice-core records. However, direct documentation of changes in surface ocean carbon content and the associated transfer of carbon to the atmosphere during deglaciations has been hindered by the lack of proxy reconstructions that unambiguously reflect the oceanic carbonate system. Radiocarbon activity tracks changes in ocean ventilation, but not in ocean carbon content, whereas proxies that record increased deglacial upwelling do not constrain the proportion of upwelled carbon that is degassed relative to that which is taken up by the biological pump. Here we apply the boron isotope pH proxy in planktic foraminifera to two sediment cores from the sub-Antarctic Atlantic and the eastern equatorial Pacific as a more direct tracer of oceanic CO2 outgassing. We show that surface waters at both locations, which partly derive from deep water upwelled in the Southern Ocean, became a significant source of carbon to the atmosphere during the last deglaciation, when the concentration of atmospheric CO2 was increasing. This oceanic CO2 outgassing supports the view that the ventilation of a deep-ocean carbon reservoir in the Southern Ocean had a key role in the deglacial CO2 rise, although our results allow for the possibility that processes operating in other regions may also have been important for the glacial-interglacial ocean-atmosphere exchange of carbon.

Replying to Levin, I. et al. Nature 486, http://dx.doi.org/10.1038/nature11175 (2012)Levin et al. report new methane data from Antarctica measured at the University of Heidelberg and combine these data with observations from two other networks to estimate long-term trends and the interhemispheric difference (IHD) in methane isotopes. These observations and the author's analysis suggest that the ?13C IHD has been mostly uniform over the last three decades. This contrasts with the Niwot Ridge, Baring Head and Pacific Ocean time series that we analysed and suggests that both fossil fuel and microbial sources remained mostly constant during the late 1980s and 1990s, following a trajectory of emissions that is more similar to the control scenario in our analysis (Fig. 2 and Supplementary Fig. 2 of Kai et al.). The estimate of ?13C inter-hemispheric difference is sensitive to different methods and selected observed sites. We note that the inter-hemispheric differences between Barrow and Cape Grim/Baring Head and between MLO and Cape Grim/Baring Head in Fig. 1 of Levin et al. were largest near the beginning of the record (circa 1990) and are broadly consistent with comparisons we made in the Supplementary Information of our paper (Supplementary Fig. 9). Important next steps, in our opinion, are (1) to use all available observations from both the Kai et al. and Levin et al. studies to assess trends in methane isotopes and their dependence on the inclusion or exclusion of individual time series, and (2) to quantify changes in microbial and fossil sources consistent with the expanded set of observations presented by Levin et al.. Even with a levelling off of both fossil and microbial sources during 1990-2005, our forward biogeochemical modelling analysis of rice agriculture provides evidence that emissions from this sector of the budget declined as a consequence of changes in fertilizer application and water management. [ABSTRACT FROM AUTHOR]

The article offers information on the research regarding the nuclear magnetic resonance (NMR) measurement on isotopes and plutonium atom's interaction.

Replying to D. J. Lacks, J. A. Van Orman & C. E. Lesher 482, 10.1038/nature10764 (2012)Lacks et al. argue that our model of isotopic fractionation in thermal gradients in silicate melts does not agree with measurements of the ratio of diffusivities seen in silicate melts. This statement is based on an over-interpretation of our model into non-steady-state applications, such as chemical fractionation, because the model we presented treats the quantized energy levels of the transition state as being equal to each other (the partition function Z(TS) = 1). This was warranted, as our main interest was in finding the steady-state solution to isotopic fractionation in a closed system (which is insensitive to the transition state). The potential importance of the transition state in determining the ratios of diffusivities of He isotopes in a geologic system has previously been noted, and future work will need to clarify the importance of the transition state for kinetic isotopic fractionation in silicate systems, particularly the ratio of diffusivities. [ABSTRACT FROM AUTHOR]

Arising from G. Dominguez, G. Wilkins & M. H. Thiemens 473, 70-73 (2011) [ABSTRACT FROM AUTHOR]

Replying to F. M. Richter 472, 10.1038/nature09954 (2011)In our Letter, we showed that the phenomenon of isotope fractionation in silicate melts by thermal diffusion, first reported in 1998 (ref. 2), can be characterised by a parameter ΔST that is independent of temperature and composition. (Here ΔST is the difference in the Soret coefficient, ST, between isotopes of a diffusing element.) Richter questioned this finding by plotting Mg isotope ratio versus temperature data (figure 1 in ref. 3) for a subset of experiments from figure 3f of ref. 1. [ABSTRACT FROM AUTHOR]

Arising from F. Huang, P. et al. 464, 396-400 (2010); Huang et al. replyIt was recently shown that relatively large (compared to analytical precision) steady state thermal isotope fractionations are produced in silicate melts whenever temperature differences are maintained for a sufficiently long time. Huang et al. reported new data on thermal isotopic fractionation of magnesium, calcium, and iron in silicate liquids, and claimed (1) that thermal isotopic fractionations in silicate liquids are independent of composition and temperature, and (2) that their 'results lead to a simple and robust framework for characterizing isotope fractionations by thermal diffusion in natural and synthetic systems'. Here I consider whether the data and arguments presented by Huang et al. support their claims. In summary, I caution against assuming (on the basis of the data presented by Huang et al.) that the thermal isotopic fractionations are independent of temperature and composition, or that a framework of the type claimed has been found. [ABSTRACT FROM AUTHOR]

The article reports that the production of six isotopes could create model for the nuclear structure of the heavier chemical elements in the periodical table.

The article reports on the move of panelists of the Nuclear Science Advisory Committee (NSAC) to call on the U.S. Department of Energy to build two dedicated isotope-production facilities worth 65 million dollars to boost the isotope programme in the country. It mentions that committee members concluded that a group of isotopes that could be used in medical therapy is vastly needed. It affirms that the creation of two new facilities to contain the isotopes could be a big help.

The article features the cycle and activities of capsules. It states that each capsule has an isotope power source, a silicon brain, and vials of living cells in stasis, and travel space between stars. It notes that capsules can send occasional status blips to other capsules, but fall silent as they spread the channels. It mentions that some capsules can scan wider spectrum and transmit data starting from Fibonacci sequences. It also describes how capsules interact with other capsules.

The article discusses the use of isotopes in quartz to reveal the age of China's Peking Man. The Peking Man fossils which belong to Homo erectus were found during archaeological excavations in the 1920s and 30s. The cave in which they were found collapsed leaving the question of their age unanswered. Topics include the collaboration of Darryl Granger and Guanjun Shen and colleagues to produce a suitable method in which the age of the fossils could reliably be determined using isotopic analysis.

The article discusses the approval by the U.S. Department of Energy (DOE) of a facility to generate rare isotopes in the fields of nuclear physics, astrophysics, and medical diagnostics. Michigan State University and Argonne National Laboratory in Illinois, competed to host the Facility of Rare Isotope Beams (FRIB). An brief overview of the facility's linear accelerator, which is the centerpiece of the FRIB, is presented.

The article reports on the success of the scientists in the U.S. in measuring the oxygen composition at the birth of the Solar System. This discovery accomplishes the top science priority of the National Aeronautics & Space Administration (NASA) Genesis probe which crashed into the Utah desert in 2004. According to Kevin McKeegan, a cosmochemist at the University of California, despite crashing, all the major objectives of Genesis will be met. The finding that the Sun is richer in oxygen-16 than the Earth contradicts the common knowledge that Earth has the same oxygen isotope composition as the Sun. The discovery also provides researchers a reference point for the oxygen composition at the origin of the Solar System.

The article reports on the discovery of the clumped isotope thermometry, a valuable tool for paleoenvironmental studies by a group of researchers at the California Institute of Technology (Caltech) in Pasadena, California. The new tool was discovered by measuring the abundance of molecules which contain oxygen-isotope and the uncommon carbon-isotope. According to published papers, the results of early test of this clumped thermometer on corals and fish earbones were promising which provides a new record of ocean temperature during Paleozoic era.

The article provides information on the composition of isotopes. Isotopes are made through a decay of radioactive nuclei which provide an evidence of how the Earth was shaped. Based on the report made by Boyet and Carlson in the Earth and Planetary Science Letters, showed some clues by measuring the abundance of neodymium isotopes in volcanic rocks. Most of these short-lived elements were produced in the events which is followed by the formation of the Solar System.

Presents a study on the analysis of measurements of argon isotopes in the mineral phlogopite. Details on the ages of phlogopite and amphibole mineral grains from the untransformed granulite lenses; Estimation of the temperature in the granulite lens during eclogite formation; Accounts on the rapid process for eclogite formation in the Bergen Arcs.

Reports on Becky Alexander and colleagues' article in the "Journal of Geophysical Research" about the isotope chemistry, known as mass-independent fractionation. History of vegetation burning and its effects on oxidation reactions in the atmosphere; Fractionation of isotopes that occurs during most chemical and physical processes; Relative contributions of liquid-phase oxidation.

Focuses on the enzyme-driven molecular discrimination which creates stable isotopes that can be thought of as natural labels on all environmental processes, allowing us to see a dynamic universe that is normally hidden from view. Functions of enzymes in catalysing chemical reactions; Requirements for understanding the contribution of processes of enzyme discrimination to the global atmosphere.

Mass spectrometry with stable isotope labels has been seminal in discovering the dynamic state of living matter, but is limited to bulk tissues or cells. We developed multi-isotope imaging mass spectrometry (MIMS) that allowed us to view and measure stable isotope incorporation with submicrometre resolution. Here we apply MIMS to diverse organisms, including Drosophila, mice and humans. We test the 'immortal strand hypothesis', which predicts that during asymmetric stem cell division chromosomes containing older template DNA are segregated to the daughter destined to remain a stem cell, thus insuring lifetime genetic stability. After labelling mice with (15)N-thymidine from gestation until post-natal week 8, we find no (15)N label retention by dividing small intestinal crypt cells after a four-week chase. In adult mice administered (15)N-thymidine pulse-chase, we find that proliferating crypt cells dilute the (15)N label, consistent with random strand segregation. We demonstrate the broad utility of MIMS with proof-of-principle studies of lipid turnover in Drosophila and translation to the human haematopoietic system. These studies show that MIMS provides high-resolution quantification of stable isotope labels that cannot be obtained using other techniques and that is broadly applicable to biological and medical research.

Geological and geochemical evidence indicates that the Antarctic ice sheet formed during the Eocene-Oligocene transition, 33.5-34.0 million years ago. Modelling studies suggest that such ice-sheet formation might have been triggered when atmospheric carbon dioxide levels (pCO2atm) fell below a critical threshold of approximately 750 p.p.m.v., but the timing and magnitude of pCO2atm relative to the evolution of the ice sheet has remained unclear. Here we use the boron isotope pH proxy on exceptionally well-preserved carbonate microfossils from a recently discovered geological section in Tanzania to estimate pCO2atm before, during and after the climate transition. Our data suggest that are reduction in pCO2atm occurred before the main phase of ice growth,followed by a sharp recovery to pre-transition values and then a more gradual decline. During maximum ice-sheet growth, pCO2atm was between approximately 450 and approximately 1,500 p.p.m.v., with a central estimate of approximately 760 p.p.m.v. The ice cap survived the period of pCO2atm recovery,although possibly with some reduction in its volume, implying (as models predict) a nonlinear response to climate forcing during melting. Overall, our results confirm the central role of declining pCO2atm in the development of the Antarctic ice sheet (in broad agreement with carbon cycle modelling) and help to constrain mechanisms and feedbacks associated with the Earth's biggest climate switch of the past 65 Myr.

Animal-like multicellular fossils appeared towards the end of the Precambrian, followed by a rapid increase in the abundance and diversity of fossils during the Early Cambrian period, an event also known as the 'Cambrian explosion'. Changes in the environmental conditions at the Precambrian/Cambrian transition (about 542 Myr ago) have been suggested as a possible explanation for this event, but are still a matter of debate. Here we report molybdenum isotope signatures of black shales from two stratigraphically correlated sample sets with a depositional age of around 542 Myr. We find a transient molybdenum isotope signal immediately after the Precambrian/Cambrian transition. Using a box model of the oceanic molybdenum cycle, we find that intense upwelling of hydrogen sulphide-rich deep ocean water best explains the observed Early Cambrian molybdenum isotope signal. Our findings suggest that the Early Cambrian animal radiation may have been triggered by a major change in ocean circulation, terminating a long period during which the Proterozoic ocean was stratified, with sulphidic deep water.

The terrestrial sediment record indicates that the Earth's climate varied drastically in the Precambrian era (before 550 million years ago), ranging from surface temperatures similar to or higher than today's to global glaciation events. The most continuous record of sea surface temperatures of that time has been derived from variations in oxygen isotope ratios of cherts (siliceous sediments), but the long-term cooling of the oceans inferred from those data has been questioned because the oxygen isotope signature could have been reset through the exchange with hydrothermal fluids after deposition of the sediments. Here we show that the silicon isotopic composition of cherts more than 550 million years old shows systematic variations with age that support the earlier conclusion of long-term ocean cooling and exclude post-depositional exchange as the main source of the isotopic variations. In agreement with other lines of evidence, a model of the silicon cycle in the Precambrian era shows that the observed silicon isotope variations imply seawater temperature changes from about 70 degrees C 3,500 million years ago to about 20 degrees C 800 million years ago.

Silicon is the second most abundant element on Earth. It is an important nutrient for phytoplankton and is readily absorbed by terrestrial vegetation; it also assists the removal of carbon dioxide from the atmosphere through the weathering of silicates. But the continental cycle of silicon is not well known, and only a few studies have attempted to use silicon stable isotopes (28Si, 29Si and 30Si) to quantify the continental silicon reservoirs. Dissolved silicon in sea and river waters forms a reservoir of mean isotopic value +1.1 per thousand (refs 7, 10). It is enriched in 30Si with respect to the igneous rocks reservoir, which has a mean isotopic value of -0.3 per thousand (refs 4, 9). This enrichment can only be produced by a major fractionation during weathering, and should result in the formation of a continental 30Si-depleted reservoir. Such a reservoir, however, has not been identified to date. Here we analyse silicon isotopes of in situ quartz from a sandstone series in France, using a new-generation secondary ion mass spectrometry apparatus. We show that quartz that precipitates as siliceous cements forms a strongly 30Si-depleted reservoir with isotopic values down to -5.7 per thousand, a more negative value than any previously published for terrestrial samples. Our findings suggest that quartz re-precipitation plays an important role in the biogeochemical cycle of silicon.

Several lines of geological and geochemical evidence indicate that the level of atmospheric oxygen was extremely low before 2.45 billion years (Gyr) ago, and that it had reached considerable levels by 2.22 Gyr ago. Here we present evidence that the rise of atmospheric oxygen had occurred by 2.32 Gyr ago. We found that syngenetic pyrite is present in organic-rich shales of the 2.32-Gyr-old Rooihoogte and Timeball Hill formations, South Africa. The range of the isotopic composition of sulphur in this pyrite is large and shows no evidence of mass-independent fractionation, indicating that atmospheric oxygen was present at significant levels (that is, greater than 10(-5) times that of the present atmospheric level) during the deposition of these units. The presence of rounded pebbles of sideritic iron formation at the base of the Rooihoogte Formation and an extensive and thick ironstone layer consisting of haematitic pisolites and oölites in the upper Timeball Hill Formation indicate that atmospheric oxygen rose significantly, perhaps for the first time, during the deposition of the Rooihoogte and Timeball Hill formations. These units were deposited between what are probably the second and third of the three Palaeoproterozoic glacial events.

The Earth's most severe glaciations are thought to have occurred about 600 million years ago, in the late Neoproterozoic era. A puzzling feature of glacial deposits from this interval is that they are overlain by 1-5-m-thick 'cap carbonates' (particulate deep-water marine carbonate rocks) associated with a prominent negative carbon isotope excursion. Cap carbonates have been controversially ascribed to the aftermath of almost complete shutdown of the ocean ecosystems for millions of years during such ice ages--the 'snowball Earth' hypothesis. Conversely, it has also been suggested that these carbonate rocks were the result of destabilization of methane hydrates during deglaciation and concomitant flooding of continental shelves and interior basins. The most compelling criticism of the latter 'methane hydrate' hypothesis has been the apparent lack of extreme isotopic variation in cap carbonates inferred locally to be associated with methane seeps. Here we report carbon isotopic and petrographic data from a Neoproterozoic postglacial cap carbonate in south China that provide direct evidence for methane-influenced processes during deglaciation. This evidence lends strong support to the hypothesis that methane hydrate destabilization contributed to the enigmatic cap carbonate deposition and strongly negative carbon isotopic anomalies following Neoproterozoic ice ages. This explanation requires less extreme environmental disturbance than that implied by the snowball Earth hypothesis.

Data from the survivors of the atomic bombs serve as the major basis for risk calculations of radiation-induced cancer in humans. A controversy has existed for almost two decades, however, concerning the possibility that neutron doses in Hiroshima may have been much larger than estimated. This controversy was based on measurements of radioisotopes activated by thermal neutrons that suggested much higher fluences at larger distances than expected. For fast neutrons, which contributed almost all the neutron dose, clear measurement validation has so far proved impossible at the large distances (900 to 1,500 m) most relevant to survivor locations. Here, the first results are reported for the detection of 63Ni produced predominantly by fast neutrons (above about 1 MeV) in copper samples from Hiroshima. This breakthrough was made possible by the development of chemical extraction methods and major improvements in the sensitivity of accelerator mass spectrometry for detection of 63Ni atoms (refs 8-11). When results are compared with 63Ni activation predicted by neutron doses for Hiroshima survivors, good agreement is observed at the distances most relevant to survivor data. These findings provide, for the first time, clear measurement validation of the neutron doses to survivors in Hiroshima.

Many independent lines of evidence document a large increase in the Earth's surface oxidation state 2,400 to 2,200 million years ago, and a second biospheric oxygenation 800 to 580 million years ago, just before large animals appear in the fossil record. Such a two-staged oxidation implies a unique ocean chemistry for much of the Proterozoic eon, which would have been neither completely anoxic and iron-rich as hypothesized for Archaean seas, nor fully oxic as supposed for most of the Phanerozoic eon. The redox chemistry of Proterozoic oceans has important implications for evolution, but empirical constraints on competing environmental models are scarce. Here we present an analysis of the iron chemistry of shales deposited in the marine Roper Basin, Australia, between about 1,500 and 1,400 million years ago, which record deep-water anoxia beneath oxidized surface water. The sulphur isotopic compositions of pyrites in the shales show strong variations along a palaeodepth gradient, indicating low sulphate concentrations in mid-Proterozoic oceans. Our data help to integrate a growing body of evidence favouring a long-lived intermediate state of the oceans, generated by the early Proterozoic oxygen revolution and terminated by the environmental transformation late in the Proterozoic eon.

Many amino acids contain an asymmetric centre, occurring as laevorotatory, L, or dextrorotatory, D, compounds. It is generally assumed that abiotic synthesis of amino acids on the early Earth resulted in racemic mixtures (L- and D-enantiomers in equal abundance). But the origin of life required, owing to conformational constraints, the almost exclusive selection of either L- or D-enantiomers, and the question of why living systems on the Earth consist of L-enantiomers rather than D-enantiomers is unresolved. A substantial fraction of the organic compounds on the early Earth may have been derived from comet and meteorite impacts. It has been reported previously that amino acids in the Murchison meteorite exhibit an excess of L-enantiomers, raising the possibility that a similar excess was present in the initial inventory of organic compounds on the Earth. The stable carbon isotope compositions of individual amino acids in Murchison support an extraterrestrial origin -- rather than a terrestrial overprint of biological amino acids-although reservations have persisted. Here we show that individual amino-acid enantiomers from Murchison are enriched in 15N relative to their terrestrial counterparts, so confirming an extraterrestrial source for an L-enantiomer excess in the Solar System that may predate the origin of life on the Earth.