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Cherts are pervasive in the Precambrian and their O and Si isotopic compositions have been used extensively for reconstructing seawater paleo-temperatures. However, these reconstructions are obscured by the fact that cherts exhibit, at a given age, a large isotopic (O and Si) heterogeneity at bulk and micrometer scales. This is understood as reflecting the fact that cherts are an assemblage of silica precursors having different origins, and that diagenesis and metamorphism have modified the isotopic compositions acquired during the last equilibration with seawater. To test the contributions of the different processes that control the Si isotopic composition of cherts, we developed high-precision triple Si isotope measurements by Multicollector-Inductively Coupled-Plasma Mass-Spectrometer (MC-ICP-MS). This approach allows to identify deviations from the equilibrium Si isotopic fractionation at the level of a few ppm. Triple Si isotope data combined with trace elements and O isotope data in Precambrian cherts demonstrate that three different sources of silica were involved in the formation of cherts, and that both equilibrium and kinetic isotopic fractionation took place for Si. Archean seawater is predicted to have a triple Si isotopic composition kinetically fractionated relative to bulk silicate Earth. This requires a large kinetic isotopic fractionation during hydrothermalism of the oceanic crust and appears consistent with warm oceans in the Precambrian. However more work is required on the triple isotope systematics of Si inputs and output to seawater by rivers and authigenic clays formation. Triple Si isotope variations can thus be used as a new tool to unravel the origin of cherts and of their O and Si isotopic compositions. The present evidence of kinetic isotopic fractionations for Si isotopes also implies that Si isotopes should be associated to triple O isotope for paleotemperature reconstructions.

H2 in a CO2 atmosphere may serve as a potential solution to the early Mars climate paradox, but its unknown sources cast doubts on the proposed mechanism. Impact cratering is an energetic process that may modify the surface redox budget. Here, we investigate the potential influence of impact-related melt oxidation and serpentinization on global climate conditions. We show that impact melt and the projectile's significant oxidizing potential during basin-forming impacts (Basin size ≥1,250 km) result in sufficient H2 to raise the global mean temperature to above 273K, which lasts for up to 105 − 106 yr considering rate-limited regime. Impact-induced serpentinization has limited consequences on the global climate in comparison. Episodic warming after large impacts may have enabled the presence of liquid water for up to several million years in the Noachian, resulting in the chemical evolution of the planet's surface co-evolving with the planetary atmosphere in an episodic manner.

We explore the heating and differentiation of rocky planets that grow by rapid pebble accretion. Our terrestrial planets grow outside of the ice line and initially accrete 28% water ice by mass. The accretion of water stops after the protoplanet reaches a mass of 0.01 ME where the gas envelope becomes hot enough to sublimate the ice and transport the vapour back to the protoplanetary disc by recycling flows. The energy released by the decay of 26Al melts the accreted ice to form clay (phyllosilicates), oxidized iron (FeO), and a water surface layer with ten times the mass of Earth's modern oceans. The ocean- atmosphere system undergoes a run-away greenhouse effect after the effective accretion temperature crosses a threshold of around 300 K. The run-away greenhouse process vaporizes the water layer, thereby trapping the accretion heat and heating the surface to more than 6000 K. This causes the upper part of the mantle to melt and form a global magma ocean. Metal melt separates from silicate melt and sediments towards the bottom of the magma ocean; the gravitational energy released by the sedimentation leads to positive feedback where the beginning differentiation of the planet causes the whole mantle to melt and differentiate. All rocky planets thus naturally experience a magma ocean stage. We demonstrate that Earth's small excess of 182W (the decay product of 182Hf) relative to the chondrites is consistent with such rapid core formation within 5 Myr followed by equilibration of the W reservoir in Earth's mantle with 182W-poor material from the core of a planetary-mass impactor, provided that the equilibration degree is at least 25- 50%, depending on the initial Hf/W ratio. The planetary collision must have occurred at least 35 Myr after the main accretion phase of the terrestrial planets.

Volatile molecules containing hydrogen, carbon, and nitrogen are key components of planetary atmospheres. In the pebble accretion model for rocky planet formation, these volatile species are accreted during the main planetary formation phase. For this study, we modelled the partitioning of volatiles within a growing planet and the outgassing to the surface. The core stores more than 90% of the hydrogen and carbon budgets of Earth for realistic values of the partition coefficients of H and C between metal and silicate melts. The magma oceans of Earth and Venus are sufficiently deep to undergo oxidation of ferrous Fe2+ to ferric Fe3+. This increased oxidation state leads to the outgassing of primarily CO2 and H2O from the magma ocean of Earth. In contrast, the oxidation state of Mars' mantle remains low and the main outgassed hydrogen carrier is H2. This hydrogen easily escapes the atmosphere due to the irradiation from the young Sun in XUV wavelengths, dragging with it the majority of the CO, CO2, H2O, and N2 contents of the atmosphere. A small amount of surface water is maintained on Mars, in agreement with proposed ancient ocean shorelines, for moderately low values of the mantle oxidation. Nitrogen partitions relatively evenly between the core and the atmosphere due to its extremely low solubility in magma; the burial of large reservoirs of nitrogen in the core is thus not possible. The overall low N contents of Earth disagree with the high abundance of N in all chondrite classes and favours a volatile delivery by pebble snow. Our model of rapid rocky planet formation by pebble accretion displays broad consistency with the volatile contents of the Sun's terrestrial planets. The diversity of the terrestrial planets can therefore be used as benchmark cases to calibrate models of extrasolar rocky planets and their atmospheres.

We present a series of papers dedicated to modelling the accretion and differentiation of rocky planets that form by pebble accretion within the lifetime of the protoplanetary disc. In this first paper, we focus on how the accreted ice determines the distribution of iron between the mantle (oxidized FeO and FeO1.5) and the core (metallic Fe and FeS). We find that an initial primitive composition of ice-rich material leads, upon heating by the decay of 26Al, to extensive water flow and the formation of clay minerals inside planetesimals. Metallic iron dissolves in liquid water and precipitates as oxidized magnetite Fe3O4. Further heating by 26Al destabilizes the clay at a temperature of around 900 K. The released supercritical water ejects the entire water content from the planetesimal. Upon reaching the silicate melting temperature of 1700 K, planetesimals further differentiate into a core (made mainly of iron sulfide FeS) and a mantle with a high fraction of oxidized iron. We propose that the asteroid Vesta's significant FeO fraction in the mantle is a testimony of its original ice content. We consider Vesta to be a surviving member of the population of protoplanets from which Mars, Earth, and Venus grew by pebble accretion. We show that the increase in the core mass fraction and decrease in FeO contents with increasing planetary mass (in the sequence Vesta - Mars - Earth) is naturally explained by the growth of terrestrial planets outside of the water ice line through accretion of pebbles containing iron that was dominantly in metallic form with an intrinsically low oxidation degree.

High precision analytical methods for 'non-traditional' stable isotopes rely upon standards for normalizing isotopic ratios, correcting instrumental mass fractionation, and comparing data between different laboratories. Zirconium isotope measurements are a new and rapidly expanding field, displaying potential for tracing the history of magmatic differentiation, as well as the formation and evolution of crustal reservoirs. However, previous studies have reported Zr isotopic data relative to different Zr standards, with the IPGP-Zr standard being most commonly used. This situation hinders direct inter-laboratory comparison thereby enlarging uncertainties when converting the data. Here the Zr isotopic composition of a new, commercially available isotopic standard ZIRC-1 is systematically calibrated relative to IPGP-Zr through a collaborative approach between two different laboratories using sample-standard bracketing and double spike methods. Moreover, the Zr isotopic composition of the certified reference materials BHVO-2 and AGV-2, alongside the widely studied Allende chondrite, is reported to ensure the robustness of our data and allow for future inter-laboratory data comparison. Consistent results are obtained from the two laboratories and the average delta Zr-94(IPGP_Zr) (the permil deviation of the Zr-94/Zr-90 of the sample from the IPGP-Zr standard) of ZIRC-1 is -0.220 +/- 0.006 parts per thousand (2SD, n = 7). The delta Zr-91(IPGP_Zr), delta Zr-92(IPGP_Zr), delta Zr-94(IPGP_Zr) and delta Zr-96(IPGP_Zr) values of ZIRC-1 follow a mass-dependent relationship. The delta Zr-94(IPGP_Zr) and delta Zr-94(ZIRC-1) values of the CV3 carbonaceous chondrite Allende are -0.041 +/- 0.021 parts per thousand and 0.179 +/- 0.022 parts per thousand (2SD, n = 7), respectively, and lower than those of bulk Earth, which has delta Zr-94(IPGP_Zr) and delta Zr-94(ZIRC-1) values of 0.041 +/- 0.041 parts per thousand and 0.261 +/- 0.041 parts per thousand respectively, according to th