Search

The last giant impact on Earth is thought to have formed the Moon 1 . The timing of this event can be determined by dating the different rocks assumed to have crystallized from the lunar magma ocean (LMO). This has led to a wide range of estimates for the age of the Moon between 4.35 and 4.51 billion years ago (Ga), depending on whether ages for lunar whole-rock samples 2-4 or individual zircon grains 5-7 are used. Here we argue that the frequent occurrence of approximately 4.35-Ga ages among lunar rocks and a spike in zircon ages at about the same time 8 is indicative of a remelting event driven by the Moon's orbital evolution rather than the original crystallization of the LMO. We show that during passage through the Laplace plane transition 9 , the Moon experienced sufficient tidal heating and melting to reset the formation ages of most lunar samples, while retaining an earlier frozen-in shape 10 and rare, earlier-formed zircons. This paradigm reconciles existing discrepancies in estimates for the crystallization time of the LMO, and permits formation of the Moon within a few tens of million years of Solar System formation, consistent with dynamical models of terrestrial planet formation 11 . Remelting of the Moon also explains the lower number of lunar impact basins than expected 12,13 , and allows metal from planetesimals accreted to the Moon after its formation to be removed to the lunar core, explaining the apparent deficit of such materials in the Moon compared with Earth 14 ., Competing Interests: Competing interests: The authors declare no competing interests., (© 2024. The Author(s).)

As the need for higher data rates for communication increases, the terahertz (THz) band has drawn considerable attention. This spectral region promises a much wider bandwidth and the transmission of large amounts of data at high speeds. However, there are still challenges that need to be addressed before the THz telecommunications technology hits the consumer market. One of the recurring concerns is that THz radiation is greatly absorbed by atmospheric water-vapor. Although many studies have presented the attenuation of THz signals under different atmospheric conditions, these results analyze specific temperature or humidity values, leaving the need for a more comprehensive analysis over a wider range of climate conditions. In this work, we present the first study of the attenuation of THz radiation over a broad range of temperatures and humidity values. It is worth noticing that all of our measurements have been undertaken at atmospheric pressure unlike many previous studies where the pressure was not kept constant for various temperatures. Furthermore, we extend our analysis beyond the impact of absolute humidity on the bit error rate in THz communications. We also discuss the refractivity of the atmosphere, examining its variations across different temperatures and humidity levels. THz propagation is studied using two different measurement systems, a long-path THz time-domain spectrometer as well as a quasi-optic setup with vector network analyze. We also compare the results with the ITU-R P.676-13 propagation model. We conclude that the attenuation at the absorption peaks increases linearly with water content and has no dependence on the temperature, while the refractive index, away from absorption lines, namely at 300 GHz shows a sub-linear increase with humidity., (© 2023. The Author(s).)

The Arabidopsis genome is methylated in CG and non-CG (CHG, and CHH in which H stands for A, T, or C) sequence contexts. DNA methylation has been suggested to be critical for seed development, and CHH methylation patterns change during stratification and germination. In plants, CHH methylation occurs mainly through the RNA-directed DNA methylation (RdDM) pathway. To test for an involvement of the RdDM pathway in chloroplast development, we analyzed seedling greening and the maximum quantum yield of photosystem II (F v /F m ) in Arabidopsis thaliana seedlings perturbed in components of that pathway. Neither seedling greening nor F v /F m in seedlings and adult plants were affected in this comprehensive set of mutants, indicating that alterations in the RdDM pathway do not affect chloroplast development. Application of inhibitors like lincomycin or norflurazon inhibits greening of seedlings and represses the expression of photosynthesis-related genes including LIGHT HARVESTING CHLOROPHYLL A/B BINDING PROTEIN1.2 (LHCB1.2) in the nucleus. Our results indicate that the LHCB1.2 promoter is poorly methylated under both control conditions and after inhibitor treatment. Therefore no correlation between LHCB1.2 mRNA transcription and methylation changes of the LHCB1.2 promoter could be established. Moreover, we conclude that perturbations in the RdDM pathway do not interfere with gun signaling.

Ferrochelatase-1 as a terminal enzyme of heme biosynthesis regulates many essential metabolic and physiological processes. Whether FC1 is involved in plant response to salt stress has not been described. This study shows that Arabidopsis overexpressing AtFC1 displays resistance to high salinity, whereas a T-DNA insertion knock-down mutant fc1 was more sensitive to salt stress than wild-type plants. AtFC1 conferred plant salt resistance by reducing Na + concentration, enhancing K + accumulation and preventing lysis of the cell membrane. Such observations were associated with the upregulation of SOS1, which encodes a plasma membrane Na + /H + antiporter. AtFC1 overexpression led to a reduced expression of several well known salt stress-responsive genes such as NHX1 and AVP1, suggesting that AtFC1-regulated low concentration of Na + in plants might not be through the mechanism for Na + sequestration. To investigate the mechanism leading to the role of AtFC1 in mediating salt stress response in plants, a transcriptome of fc1 mutant plants under salt stress was profiled. Our data show that mutation of AtFC1 led to 490 specific genes up-regulated and 380 specific genes down-regulated in fc1 mutants under salt stress. Some of the genes are involved in salt-induced oxidative stress response, monovalent cation-proton (Na + /H + ) exchange, and Na + detoxification.

The excess of highly siderophile elements in the Earth's mantle is thought to reflect the addition of primitive meteoritic material after core formation ceased. This 'late veneer' either comprises material remaining in the terrestrial planet region after the main stages of the Earth's accretion, or derives from more distant asteroidal or cometary sources. Distinguishing between these disparate origins is important because a late veneer consisting of carbonaceous chondrite-like asteroids or comets could be the principal source of the Earth's volatiles and water. Until now, however, a 'genetic' link between the late veneer and such volatile-rich materials has not been established or ruled out. Such genetic links can be determined using ruthenium (Ru) isotopes, because the Ru in the Earth's mantle predominantly derives from the late veneer, and because meteorites exhibit Ru isotope variations arising from the heterogeneous distribution of stellar-derived dust. Although Ru isotopic data and the correlation of Ru and molybdenum (Mo) isotope anomalies in meteorites were previously used to argue that the late veneer derives from the same type of inner Solar System material as do Earth's main building blocks, the Ru isotopic composition of carbonaceous chondrites has not been determined sufficiently well to rule them out as a source of the late veneer. Here we show that all chondrites, including carbonaceous chondrites, have Ru isotopic compositions distinct from that of the Earth's mantle. The Ru isotope anomalies increase from enstatite to ordinary to carbonaceous chondrites, demonstrating that material formed at greater heliocentric distance contains larger Ru isotope anomalies. Therefore, these data refute an outer Solar System origin for the late veneer and imply that the late veneer was not the primary source of volatiles and water on the Earth.

According to the most widely accepted theory of lunar origin, a giant impact on the Earth led to the formation of the Moon, and also initiated the final stage of the formation of the Earth's core. Core formation should have removed the highly siderophile elements (HSE) from Earth's primitive mantle (that is, the bulk silicate Earth), yet HSE abundances are higher than expected. One explanation for this overabundance is that a 'late veneer' of primitive material was added to the bulk silicate Earth after the core formed. To test this hypothesis, tungsten isotopes are useful for two reasons: first, because the late veneer material had a different (182)W/(184)W ratio to that of the bulk silicate Earth, and second, proportionally more material was added to the Earth than to the Moon. Thus, if a late veneer did occur, the bulk silicate Earth and the Moon must have different (182)W/(184)W ratios. Moreover, the Moon-forming impact would also have created (182)W differences because the mantle and core material of the impactor with distinct (182)W/(184)W would have mixed with the proto-Earth during the giant impact. However the (182)W/(184)W of the Moon has not been determined precisely enough to identify signatures of a late veneer or the giant impact. Here, using more-precise measurement techniques, we show that the Moon exhibits a (182)W excess of 27 ± 4 parts per million over the present-day bulk silicate Earth. This excess is consistent with the expected (182)W difference resulting from a late veneer with a total mass and composition inferred from HSE systematics. Thus, our data independently show that HSE abundances in the bulk silicate Earth were established after the giant impact and core formation, as predicted by the late veneer hypothesis. But, unexpectedly, we find that before the late veneer, no (182)W anomaly existed between the bulk silicate Earth and the Moon, even though one should have arisen through the giant impact. The origin of the homogeneous (182)W of the pre-late-veneer bulk silicate Earth and the Moon is enigmatic and constitutes a challenge to current models of lunar origin.

The Moon is thought to have formed from debris ejected by a giant impact with the early 'proto'-Earth and, as a result of the high energies involved, the Moon would have melted to form a magma ocean. The timescales for formation and solidification of the Moon can be quantified by using 182Hf-182W and 146Sm-142Nd chronometry, but these methods have yielded contradicting results. In earlier studies, 182W anomalies in lunar rocks were attributed to decay of 182Hf within the lunar mantle and were used to infer that the Moon solidified within the first approximately 60 million years of the Solar System. However, the dominant 182W component in most lunar rocks reflects cosmogenic production mainly by neutron capture of 181Ta during cosmic-ray exposure of the lunar surface, compromising a reliable interpretation in terms of 182Hf-182W chronometry. Here we present tungsten isotope data for lunar metals that do not contain any measurable Ta-derived 182W. All metals have identical 182W/184W ratios, indicating that the lunar magma ocean did not crystallize within the first approximately 60 Myr of the Solar System, which is no longer inconsistent with Sm-Nd chronometry. Our new data reveal that the lunar and terrestrial mantles have identical 182W/184W. This, in conjunction with 147Sm-143Nd ages for the oldest lunar rocks, constrains the age of the Moon and Earth to Myr after formation of the Solar System. The identical 182W/184W ratios of the lunar and terrestrial mantles require either that the Moon is derived mainly from terrestrial material or that tungsten isotopes in the Moon and Earth's mantle equilibrated in the aftermath of the giant impact, as has been proposed to account for identical oxygen isotope compositions of the Earth and Moon.

The timescales and mechanisms for the formation and chemical differentiation of the planets can be quantified using the radioactive decay of short-lived isotopes. Of these, the (182)Hf-to-(182)W decay is ideally suited for dating core formation in planetary bodies. In an earlier study, the W isotope composition of the Earth's mantle was used to infer that core formation was late (> or = 60 million years after the beginning of the Solar System) and that accretion was a protracted process. The correct interpretation of Hf-W data depends, however, on accurate knowledge of the initial abundance of (182)Hf in the Solar System and the W isotope composition of chondritic meteorites. Here we report Hf-W data for carbonaceous and H chondrite meteorites that lead to timescales of accretion and core formation significantly different from those calculated previously. The revised ages for Vesta, Mars and Earth indicate rapid accretion, and show that the timescale for core formation decreases with decreasing size of the planet. We conclude that core formation in the terrestrial planets and the formation of the Moon must have occurred during the first approximately 30 million years of the life of the Solar System.

Matrix metalloproteinases are a family of zinc endopeptidases involved in tissue remodelling. They have been implicated in various disease processes including tumour invasion and joint destruction. These enzymes consist of several domains, which are responsible for latency, catalysis and substrate recognition. Human neutrophil collagenase (PMNL-CL, MMP-8) represents one of the two 'interstitial' collagenases that cleave triple helical collagens types I, II and III. Its 163 residue catalytic domain (Met80 to Gly242) has been expressed in Escherichia coli and crystallized as a non-covalent complex with the inhibitor Pro-Leu-Gly-hydroxylamine. The 2.0 A crystal structure reveals a spherical molecule with a shallow active-site cleft separating a smaller C-terminal subdomain from a bigger N-terminal domain, composed of a five-stranded beta-sheet, two alpha-helices, and bridging loops. The inhibitor mimics the unprimed (P1-P3) residues of a substrate; primed (P1'-P3') peptide substrate residues should bind in an extended conformation, with the bulky P1' side-chain fitting into the deep hydrophobic S1' subsite. Modelling experiments with collagen show that the scissile strand of triple-helical collagen must be freed to fit the subsites. The catalytic zinc ion is situated at the bottom of the active-site cleft and is penta-coordinated by three histidines and by both hydroxamic acid oxygens of the inhibitor. In addition to the catalytic zinc, the catalytic domain harbours a second, non-exchangeable zinc ion and two calcium ions, which are packed against the top of the beta-sheet and presumably function to stabilize the catalytic domain.(ABSTRACT TRUNCATED AT 250 WORDS)