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The activation of abundant molecules such as hydrocarbons and atmospheric nitrogen (N2) remains a challenge because these molecules are often inert. The formation of carbon–nitrogen bonds from N2 typically has required reactive organic precursors that are incompatible with the reducing conditions that promote N2 reactivity1, which has prevented catalysis. Here we report a diketiminate-supported iron system that sequentially activates benzene and N2 to form aniline derivatives. The key to this coupling reaction is the partial silylation of a reduced iron–dinitrogen complex, followed by migration of a benzene-derived aryl group to the nitrogen. Further reduction releases N2-derived aniline, and the resulting iron species can re-enter the cyclic pathway. Specifically, we show that an easily prepared diketiminate iron bromide complex2 mediates the one-pot conversion of several petroleum-derived arenes into the corresponding silylated aniline derivatives, by using a mixture of sodium powder, crown ether, trimethylsilyl bromide and N2 as the nitrogen source. Numerous compounds along the cyclic pathway are isolated and crystallographically characterized, and their reactivity supports a mechanism for sequential hydrocarbon activation and N2 functionalization. This strategy couples nitrogen atoms from N2 with abundant hydrocarbons, and maps a route towards future catalytic systems. An iron complex sequentially activates N2 and C–H bonds in benzene to form aniline, with coupling achieved through partial silylation of a reduced iron–nitrogen complex and phenyl migration.

Homologous recombination repairs DNA double-strand breaks and must function even on actively transcribed DNA. Because break repair prevents chromosome loss, the completion of repair is expected to outweigh the transcription of broken templates. However, the interplay between DNA break repair and transcription processivity is unclear. Here we show that the transcription factor GreA inhibits break repair in Escherichia coli. GreA restarts backtracked RNA polymerase and hence promotes transcription fidelity. We report that removal of GreA results in markedly enhanced break repair via the classic RecBCD-RecA pathway. Using a deep-sequencing method to measure chromosomal exonucleolytic degradation, we demonstrate that the absence of GreA limits RecBCD-mediated resection. Our findings suggest that increased RNA polymerase backtracking promotes break repair by instigating RecA loading by RecBCD, without the influence of canonical Chi signals. The idea that backtracked RNA polymerase can stimulate recombination presents a DNA transaction conundrum: a transcription fidelity factor that compromises genomic integrity.

The Earth and Moon have iron isotopic abundances that are slightly 'heavy' compared with Mars, the asteroid Vesta and primitive meteorites. The reason for this has been unclear. One suggestion is that there was a large-scale isotopic equilibration during the 'giant impact', the collision between the early Earth and a Mars-sized body that created the Moon, but this has seemed unlikely given that most other elements do not show the effect. An analysis of 44 meteorite and terrestrial samples now shows that the silicon isotopic compositions of basaltic rocks from the Earth and Moon are also distinctly heavy. The finding is consistent with the isotopic equilibration model, and it suggests that silicon was already partitioned into the Earth's core as a light element before the Moon formed. The silicon isotopic compositions of basaltic rocks from the Earth and Moon are distinctly 'heavy'. The similar isotopic composition of the bulk silicate Earth and the Moon are consistent with large-scale isotopic equilibration during the 'giant impact', indicating that Si was already a light element in the Earth's core before the Moon formed. Small isotopic differences between the silicate minerals in planets may have developed as a result of processes associated with core formation, or from evaporative losses during accretion as the planets were built up. Basalts from the Earth and the Moon do indeed appear to have iron isotopic compositions that are slightly heavy relative to those from Mars, Vesta and primitive undifferentiated meteorites1,2,3,4 (chondrites). Explanations for these differences have included evaporation during the ‘giant impact’ that created the Moon (when a Mars-sized body collided with the young Earth). However, lithium5 and magnesium6, lighter elements with comparable volatility7,8,9, reveal no such differences, rendering evaporation unlikely as an explanation. Here we show that the silicon isotopic compositions of basaltic rocks from the Earth and the Moon are also distinctly heavy. A likely cause is that silicon is one of the light elements in the Earth’s core. We show that both the direction and magnitude of the silicon isotopic effect are in accord with current theory10 based on the stiffness of bonding in metal and silicate. The similar isotopic composition of the bulk silicate Earth and the Moon is consistent with the recent proposal11 that there was large-scale isotopic equilibration during the giant impact. We conclude that Si was already incorporated as a light element in the Earth’s core before the Moon formed.

Fresh evidence shows that the iron isotopic composition of Earth's silicate component does not, as was previously thought, reflect the formation of the planet's core at high pressure nor losses of material to space.

Continental crust forms from, and thus chemically depletes, the Earth's mantle. Evidence that the Earth's mantle was already chemically depleted by melting before the formation of today's oldest surviving crust has been presented in the form of Sm–Nd isotope studies of 3.8–4.0 billion years old rocks from Greenland1,2,3,4,5 and Canada5,6,7. But this interpretation has been questioned because of the possibility that subsequent perturbations may have re-equilibrated the neodymium-isotope compositions of these rocks8. Independent and more robust evidence for the origin of the earliest crust and depletion of the Archaean mantle can potentially be provided by hafnium-isotope compositions of zircon, a mineral whose age can be precisely determined by U–Pb dating, and which can survive metamorphisms4. But the amounts of hafnium in single zircon grains are too small for the isotopic composition to be precisely analysed by conventional methods. Here we report hafnium-isotope data, obtained using the new technique of multiple-collector plasma-source mass spectrometry9, for 37 individual grains of the oldest known terrestrial zircons (from the Narryer Gneiss Complex, Australia, with U–Pb ages of up to 4.14 Gyr (10–13). We find that none of the grains has a depleted mantle signature, but that many were derived from a source with a hafnium-isotope composition similar to that of chondritic meteorites. Furthermore, more than half of the analysed grains seem to have formed by remelting of significantly older crust, indicating that crustal preservation and subsequent reworking might have been important processes from earliest times.

Meteorite chronometry based on the 182Hf–182W system can provide powerful constraints on the timing of planetary accretion and differentiation1,2,3,4, although the full potential of this method has yet to be realized. For example, no measurements have been made on the silicate-rich portions of planets and planetesimals other than the Earth and Moon. Here we report tungsten isotope compositions for two eucrites, thought to be derived from asteroid 4 Vesta, and from eight other basaltic achondritic meteorites that are widely considered to be from Mars. The eucrites, which are among the oldest differentiated meteorites, yield exceedingly radiogenic tungsten, indicating rapid accretion, differentiation and core formation on Vesta within the first 5–15 Myr of Solar System history, whereas the range of radiogenic tungsten measurements on the martian meteorites points towards tungsten depletion via melting and core formation within the first 30 Myr of the Solar System. The survival of tungsten isotope heterogeneity in the martian upper mantle implies that no giant impacts or large-scale convective mixing took place since this time. These results contrast with those obtained for the Earth–Moon system2,3 for which accretion and core formation related to giant impacts appears to have continued for at least an additional 20 Myr.

THE accretion of the Earth and Moon within the solar nebula is thought1–3 to have taken 50 to 100 million years. But the timing of formation of the Earth's core has been controversial, with some4,5 proposing that it took place within the first 15 Myr of Earth's accretion history and others6,7 proposing that it occurred after 50 Myr of accretion. Meteorite chronometry based on the 182Hf–182W system has the potential to resolve this debate, as segregation of a metal core from silicates should induce strong fractionation of hafnium from tungsten. Here we report tungsten isotope compositions for two iron meteorites, two carbonaceous chondrites, and a lunar mare basalt. We see clear 182W deficits in both iron meteorites, in agreement with previous results4,5. But the data for chondrites are inconsistent with the hypothesis of early core formation, suggesting that both this event and the formation of the Moon must have occurred at least 62 ± 10 Myr after the iron meteorites formed.

The Solar System has a largely uniform isotopic composition but with tantalizing small variations. Geochemists are trying to ascertain the mechanisms and types of stars that produced this state of affairs.

Accumulation of prion protein during prion replication causes persistent translational repression of global protein synthesis, which is mediated by eIF2α-P and is associated with synaptic failure and neuronal loss in prion-diseased mice; promoting translational recovery in hippocampi of prion-infected mice is neuroprotective. Despite extensive research, the mechanisms leading to neuronal loss in neurodegenerative disease are still little understood, and no treatments or promising treatment strategies exist. Using prion-diseased mice as a model, this study demonstrates that the accumulation of misfolded prion protein during prion replication causes persistent translational repression of global protein synthesis. This is mediated by eIF2α-P and is associated with synaptic failure and neuronal loss in prion-diseased mice. Promoting translational recovery in the hippocampi of prion-infected mice is neuroprotective, suggesting that a generic approach involving the fine-tuning of protein synthesis may be worth pursuing in prion diseases, and perhaps in other neurodegenerative disorders involving protein misfolding. The mechanisms leading to neuronal death in neurodegenerative disease are poorly understood. Many of these disorders, including Alzheimer’s, Parkinson’s and prion diseases, are associated with the accumulation of misfolded disease-specific proteins. The unfolded protein response is a protective cellular mechanism triggered by rising levels of misfolded proteins. One arm of this pathway results in the transient shutdown of protein translation, through phosphorylation of the α-subunit of eukaryotic translation initiation factor, eIF2. Activation of the unfolded protein response and/or increased eIF2α-P levels are seen in patients with Alzheimer’s, Parkinson’s and prion diseases1,2,3,4, but how this links to neurodegeneration is unknown. Here we show that accumulation of prion protein during prion replication causes persistent translational repression of global protein synthesis by eIF2α-P, associated with synaptic failure and neuronal loss in prion-diseased mice. Further, we show that promoting translational recovery in hippocampi of prion-infected mice is neuroprotective. Overexpression of GADD34, a specific eIF2α-P phosphatase, as well as reduction of levels of prion protein by lentivirally mediated RNA interference, reduced eIF2α-P levels. As a result, both approaches restored vital translation rates during prion disease, rescuing synaptic deficits and neuronal loss, thereby significantly increasing survival. In contrast, salubrinal, an inhibitor of eIF2α-P dephosphorylation5, increased eIF2α-P levels, exacerbating neurotoxicity and significantly reducing survival in prion-diseased mice. Given the prevalence of protein misfolding and activation of the unfolded protein response in several neurodegenerative diseases, our results suggest that manipulation of common pathways such as translational control, rather than disease-specific approaches, may lead to new therapies preventing synaptic failure and neuronal loss across the spectrum of these disorders.

It has long been thought that the Earth had a protracted and complex history of volatile accretion and loss. Albarede paints a different picture, proposing that the Earth first formed as a dry planet which, like the Moon, was devoid of volatile constituents. He suggests that the Earth's complement of volatile elements was only established later, by the addition of a small veneer of volatile-rich material at ∼100 Myr (here and elsewhere, ages are relative to the origin of the Solar System). Here we argue that the Earth's mass balance of moderately volatile elements is inconsistent with Albarede's hypothesis but is well explained by the standard model of accretion from partially volatile-depleted material, accompanied by core formation.

The lavas of the Cameroon line display a lead isotope anomaly at the continent/ocean boundary which can be attributed to a fossil mantle plume, the diminishing lateral effects of which can be recognized as far as 400km to either side. The high 206Pb/204Pb ratio—characteristic of the mantle endmember known as 'HIMU'—seems to arise from U/Pb fractionation accompanying melt migration following emplacement of the plume in the upper mantle 125 Myr ago.

MISSISSIPPI Valley type (MVT) ore deposits commonly consist of some combination of lead, zinc and iron sulphides accompanied by barite, fluorite, dolomite and calcite. They are thought to form by fluid expulsion from sedimentary successions1–3,but their exact origin has remained controversial because of the scarcity of reliable geochronological data. In a recent and widely quoted model the MVT deposits of the central and eastern United States formed as a result of large-scale lateral fluid flow driven by the tectonic squeezing of sedimentary successions during the late Palaeozoic Alleghenian orogeny (330–250 Myr)4. Here we report the first direct Rb–Sr dating of sphalerites from an MVT deposit and propose this as a useful geochronological technique for sulphide mineralization with poor age control. Rb–Sr data for sphalerites from Coy mine, East Tennessee, define an isochron age of 377 ± 29 Myr, ruling out any genetic connection with the Alleghenian orogeny. Instead, MVT mineralization in the eastern United States was apparently generated from fluids expelled during thrusting associated with the older Acadian orogeny (380–350 Myr).

Ocean island basalts are generally thought to be the surface expression of mantle plumes, but the nature of the components in the source regions of such mantle plumes is a subject of long-standing debate. The lavas erupted at Hawaii have attracted particular attention, as it has been proposed that coupled 186Os and 187Os anomalies reflect interaction with the Earth's metallic core. It has recently been suggested, however, that such variations could also result from addition of oceanic ferromanganese sediments to the mantle source of these lavas. Here we show that Hawaiian picrites with osmium isotope anomalies also exhibit pronounced thallium isotope variations, which are coupled with caesium/thallium ratios that extend to values much lower than commonly observed for mantle-derived rocks. This correlation cannot be created by admixing of core material, and is best explained by the addition of ferromanganese sediments into the Hawaii mantle source region. However, the lack of correlation between thallium and osmium isotopes and the high thallium/osmium ratios of ferromanganese sediments preclude a sedimentary origin for the osmium isotope anomalies, and leaves core-mantle interaction as a viable explanation for the osmium isotope variations of the Hawaiian picrites.