Age of meteorites and the earth
Abstract
Within experimental error, meteorites have one age as determined by three independent radiometric methods. The most accurate method (Pb207/Pb206 gives an age of 4.55 ± 0.07 × 109 yr. Using certain assumptions which are apparently justified, one can define the isotopic evolution of lead for any meteoritic body. It is found that earth lead meets the requirements of this definition. It is therefore believed that the age for the earth is the same as for meteorites. This is the time since the earth attained its present mass
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Cited by (296)
The global lead isotope system: Toward a new framework reflecting Earth's dynamic evolution
2023, Earth-Science ReviewsThe U-Th-Pb system is perhaps one of the most versatile isotopic systems in use by Earth scientists, widely applied to both date and compositionally trace geological events through Earth history. However, the Pb isotope systematics of the Earth are subject to two major paradoxes. Assuming our planet evolved uniformly from a chondritic composition, all the present-day Earth chemical reservoirs should plot on the 4.55 Ga meteorite isochron, also known as the geochron; but in fact, all known reservoirs are more radiogenic (having excess 206Pb and 207Pb) than the carbonaceous chondrites, constituting the first Pb paradox. The second Pb paradox (also called the kappa conundrum) is the apparent difference between the measured 232Th/238U ratio (κ) of oceanic basalts and the time-integrated 232Th/238U ratio (κPb) predicted from the Pb isotope ratios. While significant progress has been made since the realization of the two Pb paradoxes over 50 years ago, the persistence of these issues highlights the limitations in our current understanding of the Earth's evolution with respect to U, Th and Pb, as we are neither able to ascertain the composition of the present-day bulk silicate Earth (BSE; comprising Earth's mantle and its crust) nor to determine the starting time(s) of U/Pb and Th/U fractionations in the mantle. In this contribution, we first review the Pb paradoxes and their proposed solutions. We then discuss the previously proposed Pb evolution models and establish a new framework based on a reassessment of global data and current understanding of Earth dynamics. Our model invokes the presence of distinct Pb isotope evolution paths for a diverse range of segregated components of the BSE, with the present-day upper continental crust being one of the end members. The model also features a two-stage Pb evolution for the silicate Earth, with a data-defined ca. 3.2 Ga start time for major compositional differentiation and remixing, possibly due to the initiation of global plate tectonics at that time. We readdress the first Pb paradox through recognizing that, to the first order, the Pb isotopic values of present-day Earth materials lie on a Pb differentiation line defined by our re-estimated present-day BSE and continental crust, and proposing that the data plot mostly to the right of the geochron due to second-order complications caused by both source mixing and fractionation of Earth materials. We argue that rocks found on Earth's surface mostly originated from more radiogenic reservoirs (with HIMU being an end member) at shallower levels, where long-term gravitational differentiation and subduction-led mantle remixing preferentially concentrated more radiogenic materials. We also largely mitigated the second Pb paradox through an updated κ vs. κpb plot using modern global databases, which shows a general agreement between the mean κ and κpb values. We further demonstrate that the choice of Pb evolution models has potentially profound implications when applying non-radiogenic Pb corrections during U-Pb dating of Earth materials.
Formation of juvenile continental crust in northern Nubian Shield: New evidence from granitic zircon U-Pb-Hf-O isotopes
2022, Precambrian ResearchThe Neoproterozoic Arabian-Nubian Shield (ANS) consists of continental crust formed prior to and during the collision between East and West Gondwana. The Eastern Desert of Egypt (i.e., northern Nubian Shield) constitutes the north-western part of the ANS. Neoproterozoic magmatism in the Eastern Desert region occurred between ∼ 800 Ma and ∼ 550 Ma. Although there is a broad consensus that ∼ 800–650 Ma pre-collisional igneous rocks comprise the main magmatic stage contributing to Eastern Desert crustal evolution, whether this crust is purely of a juvenile composition, or was generated by recycling/reworking of much older continental crust, remains debated. Here, we present new whole-rock geochemical and Sr-Nd isotopic data and an integrated zircon U-Pb-Hf-O-trace element dataset for two granitoids (Um Khariga and Genina Gharbia) from the Eastern Desert. Samples from the Um Khariga granitoids yield zircon U-Pb ages of 746 ± 4 and 753 ± 4 Ma that overlap within error, and the Genina Gharbia granitoids have an age of ∼ 690 Ma, indicating that both granitoids belong to different phases of pre-collisional magmatism. Zircon hafnium isotopic data of both granitoids yield weighted mean εHf(t) values ranging from + 8.01 ± 0.23 to + 10.52 ± 0.13, indicating that both granitoid suites were derived by melting of a juvenile source. SIMS oxygen isotope data for zircon show that the magmatic zircon has mantle-like δ18O values with weighted means ranging from 4.73 ± 0.02 to 5.04 ± 0.08 ‰. Based on previously published zircon U-Pb-Hf-O-trace element data for granitoids and volcanic rocks of the Eastern Desert, plus our new isotopic datasets obtained from the Um Khariga and Genina Gharbia granitoids, we show that the ∼ 800–650 Ma magmatism is characterized by high zircon εHf(t) (+8 to + 15), and mantle-like zircon δ18O values (∼+5‰), implying that the continental crust of the Eastern Desert was either extracted directly from a depleted mantle and/or reworked from accreted juvenile oceanic crust or oceanic arc with no evidence for the input of old continental material. The overall zircon εHf(t) and δ18O evolution trends for the northern Nubian Shield show that juvenile mantle input dominated the early phases (ca. 800–670 Ma) of crustal growth and evolution in this part of the ANS, coinciding with the break-up stage of the supercontinent Rodinia. The involvement of continental crustal recycling only started to play a significant role since the ca. 670 Ma regional collisional event during the early stage of Gondwana assembly.
Combined U-Pb isotopic signatures of U mill tailings from France and Gabon: A new potential tracer to assess their fingerprint on the environment
2022, Journal of Hazardous MaterialsUranium milling activities have produced high volumes of long-lived radioactive processed wastes stored worldwide in near surface environment. The aim of this study is to highlight relevant tracers that can be used for environmental impact assessment studies involving U mill tailings. A multi-tracer study involving elemental content, 238U decay products disequilibria and stable Pb isotopes was performed in different types of U mill tailings (alkaline, acid, neutralized acid) collected from five Tailings Management Facilities in France (Le Bosc, L’Ecarpière, Le Bernardan, and Bellezane) and Gabon (Mounana). Our results showed that U and Pb concentrations range between 30 and 594 ppm and 66–805 ppm, respectively. These tailings have a strong disequilibrium of (234U/238U) and (230Th/238U) activity ratios (1.27–1.87 and 6–65, respectively), as well as higher 206Pb/207Pb (1.86–7.15) and lower 208Pb/207Pb (0.22–2.39) compared to geochemical background ((234U/238U) and (230Th/238U) equal to unity; 206Pb/207Pb = 1.20; 208Pb/207Pb = 2.47). In situ analyzes (SEM, SIMS) showed that Pb-bearing phases with high 206Pb/207Pb are related to remaining U-rich phases, S-rich phases and potentially clay minerals or oxyhydroxides. We suggest that the combination of the 206Pb/207Pb with the (234U/238U) ratio is a relevant tool for the fingerprinting of the impact of U milling activities on the environment.
What fuel properties enable higher thermal efficiency in spark-ignited engines?
2021, Progress in Energy and Combustion ScienceThe Co-Optimization of Fuels and Engines (Co-Optima) initiative from the US Department of Energy aims to co-develop fuels and engines in an effort to maximize energy efficiency and the utilization of renewable fuels. Many of these renewable fuel options have fuel chemistries that are different from those of petroleum-derived fuels. Because practical market fuels need to meet specific fuel-property requirements, a chemistry-agnostic approach to assessing the potential benefits of candidate fuels was developed using the Central Fuel Property Hypothesis (CFPH). The CFPH states that fuel properties are predictive of the performance of the fuel, regardless of the fuel's chemical composition. In order to use this hypothesis to assess the potential of fuel candidates to increase efficiency in spark-ignition (SI) engines, the individual contributions towards efficiency potential in an optimized engine must be quantified in a way that allows the individual fuel properties to be traded off for one another. This review article begins by providing an overview of the historical linkages between fuel properties and engine efficiency, including the two dominant pathways currently being used by vehicle manufacturers to reduce fuel consumption. Then, a thermodynamic-based assessment to quantify how six individual fuel properties can affect efficiency in SI engines is performed: research octane number, octane sensitivity, latent heat of vaporization, laminar flame speed, particulate matter index, and catalyst light-off temperature. The relative effects of each of these fuel properties is combined into a unified merit function that is capable of assessing the fuel property-based efficiency potential of fuels with conventional and unconventional compositions.
High-performance FRET biosensors for single-cell and in vivo lead detection
2020, Biosensors and BioelectronicsForms of lead (Pb) have been insidiously invading human life for thousands of years without obvious signs of their considerable danger to human health. Blood lead level (BLL) is the routine measure used for diagnosing the degree of lead intoxication, although it is unclear whether there is any safe range of BLL. To develop a practical detection tool for living organisms, we engineered a genetically encoded fluorescence resonance energy transfer (FRET)-based Pb2+ biosensor, ‘Met-lead 1.44 M1’, with excellent performance. Met-lead 1.44 M1 has an apparent dissociation constant (Kd) of 25.97 nM, a detection limit (LOD) of 10 nM (2.0 ppb/0.2 μg/dL), and an enhancement dynamic ratio of nearly ~ 5-fold upon Pb2+ binding. The 10 nM sensitivity of Met-lead 1.44 M1 is five times below the World Health Organization-permitted level of lead in tap water (10 ppb; WHO, 2017), and fifteen times lower than the maximum BLL for children (3 μg/dL). We deployed Met-lead 1.44 M1 to measure Pb2+ concentrations in different living models, including two general human cell lines and one specific line, induced pluripotent stem cell (iPSC)-derived cardiomyocytes, as well as in widely used model species in plant (Arabidopsis thaliana) and animal (Drosophila melanogaster) research. Our results suggest that this new biosensor is suitable for lead toxicological research in vitro and in vivo, and will pave the way toward potential applications for both low BLL measures and rapid detection of environmental lead in its divalent form.
The trace element and radiogenic isotope systematics of clinopyroxene have frequently been used to characterise mantle metasomatic processes, because it is the main host of most lithophile elements in the lithospheric mantle. To further our understanding of mantle metasomatism, both solution-mode Sr-Nd-Hf-Pb and in situ trace element and Sr isotopic data have been acquired for clinopyroxene grains from a suite of peridotite (lherzolites and wehrlites), MARID (Mica-Amphibole-Rutile-Ilmenite-Diopside), and PIC (Phlogopite-Ilmenite-Clinopyroxene) rocks from the Kimberley kimberlites (South Africa). The studied mantle samples can be divided into two groups on the basis of their clinopyroxene trace element compositions, and this subdivision is reinforced by their isotopic ratios. Type 1 clinopyroxene, which comprises PIC, wehrlite, and some sheared lherzolite samples, is characterised by low Sr (~100–200 ppm) and LREE concentrations, moderate HFSE contents (e.g., ~40–75 ppm Zr; La/Zr < 0.04), and restricted isotopic compositions (e.g., 87Sr/86Sri = 0.70369–0.70383; εNdi = +3.1 to +3.6) resembling those of their host kimberlite magmas. Available trace element partition coefficients can be used to show that Type 1 clinopyroxenes are close to being in equilibrium with kimberlite melt compositions, supporting a genetic link between kimberlites and these metasomatised lithologies. Thermobarometric estimates for Type 1 samples in this study indicate equilibration depths of 135–160 km within the lithosphere, thus showing that kimberlite melt metasomatism is prevalent in the deeper part of the lithosphere beneath Kimberley. In contrast, Type 2 clinopyroxenes occur in MARID rocks and coarse granular lherzolites in this study, which derive from shallower depths (<135 km), and have higher Sr (~350–1000 ppm) and LREE contents, corresponding to higher La/Zr of > ~ 0.05. The isotopic compositions of Type 2 clinopyroxenes are more variable and extend from compositions resembling the “enriched mantle” towards those of Type 1 rocks (e.g., εNdi = −12.7 to −4.4). To constrain the source of these variations, in situ Sr isotope analyses of clinopyroxene were undertaken, including zoned grains in Type 2 samples. MARID and lherzolite clinopyroxene cores display generally radiogenic but variable 87Sr/86Sri values (0.70526–0.71177), which are correlated with Sr contents and La/Zr ratios, and which might be explained by the interaction between peridotite and melts from different enriched sources within the lithospheric mantle. Most notably, the rims of these Type 2 clinopyroxenes trend towards compositions similar to those of the host kimberlite and Type 1 clinopyroxene from PIC and wehrlites. These results are interpreted to represent clinopyroxene overgrowth during late-stage (shortly before/during entrainment) metasomatism by kimberlite magmas. Our study shows that a pervasive, alkaline metasomatic event caused MARID to be generated and harzburgites to be converted to lherzolite in the lithospheric mantle beneath the Kimberley area, which was followed by kimberlite metasomatism during Cretaceous magmatism. This latter event is the time at which discrete PIC, wehrlite, and sheared lherzolite lithologies were formed, and MARID and granular lherzolites were partly modified.