Planetary atmospheres cannot remain hydrostatic at all altitudes because they approach finite density at infinite radius, implying infinite mass. Classical treatments address this in two directions: either retain a hydrostatic structure while allowing particles in the high-velocity tail to decouple and escape in a Jeans-type manner, or promote the gas to a continuum outflow to obtain a transonic Parker-type solution. The usual criterion compares the local mean free path to the sonic point radius. If the mean free path is shorter, the atmosphere is hydrostatic with an imposed Jeans escape flux; if it is longer, the gas is hydrodynamic with Jeans escape neglected. Here, we show that hydrogen-rich atmospheres do not separate cleanly into hydrodynamic and Jeans-escape regimes. At any radius, some particles still collide and behave as a fluid, while others have already experienced their last collision and move collisionlessly on ballistic trajectories. The relative importance of these two behaviors changes smoothly with radius rather than switching at a single boundary. The hydrodynamic channel accelerates and passes through a sonic point, whereas the collisionless channel decelerates under gravity and grows with altitude, removing mass and momentum from the collisional flow. As the collisionless component grows, the bulk flow speed reaches a maximum and then decelerates thereafter, producing profiles similar to Parker breeze solutions even though escape is carried by the collisionless channel. This two-channel framework provides a first step toward a self-consistent treatment that unifies hydrodynamics and kinetics in atmospheric loss models.

The Ontong Java Plateau, mainly emplaced during the Early Cretaceous on the Pacific Plate, is the most voluminous extant oceanic plateau. The exceptional volume and flux of magma that formed this plateau is widely thought to result from melting induced by a hot, buoyant mantle plume head; however, a purely thermal plume predicts uplift to above sea level, inconsistent with the plateau's mostly submarine emplacement. An alternative formation mechanism is rapid seafloor spreading inducing decompression melting of a mantle portion with a relatively high proportion of dense fusible component. Here we use thermodynamic models simulating decompression melting of heterogeneous mantle sources to constrain the mantle potential temperatures and dense fusible mantle proportions required to form the Ontong Java Plateau under mantle plume and seafloor spreading scenarios. We show that the seafloor spreading model requires an unreasonably high mantle potential temperature or dense fusible pyroxenite proportion. By contrast, a thermochemical plume, with a temperature 135-200 degrees C higher than ambient mantle and up to 13% dense fusible pyroxenite, can explain not only the spatial variations in crustal thickness and lava compositions of the plateau, but also its mostly submarine emplacement. Thus, we propose that the formation of this plateau is best explained by a thermochemical mantle plume.

The extreme conditions in the early stages of planetary evolution are thought to shape its subsequent development. High internal temperatures from giant impacts can provide sufficient energy to drive extreme volatile loss, with hydrogen being most readily lost. However, the conditions required for maintaining a primordial atmosphere over geological timescales remain enigmatic. This paper revisits the core powered mass loss model for hydrogen removal from planetary atmospheres. One popular approach is to combine mass continuity at the sonic point with an energy-based constraint. We demonstrate that the so-called “energy limited” component of this model is unnecessary because atmospheric loss following giant impacts is governed solely by conditions at the sonic point. By simulating a broad range of synthetic exoplanets, varying in planetary mass, atmospheric mass fraction, and temperature, we find that the “energy limited” model can underestimate the mass loss rates by up to eight orders of magnitude. Our findings suggest that, for sufficiently hot post-impact surface conditions, hydrogen rich atmospheres can be removed on dynamical timescales that are far shorter than one million years.

The thermal evolution of Earth's mantle is a fundamental problem in geosciences, yet proposed models often focus narrowly on producing estimates of past mantle potential temperature without simultaneously satisfying independent constraints imposed by whole-Earth energy balance and geological observations. In this review, we synthesize key constraints on mantle potential temperature over geological time, with particular emphasis on petrological estimates derived from primary magmas and their consistency with global thermal budget considerations inferred from geophysical and geochemical data. We show that the most reliable petrological estimates imply a present-day Urey ratio of similar to 0.25. We then examine the implications of different heat-flow scaling laws, assess the geophysical plausibility of various thermal histories, and clarify the roles of surface heat flux, mantle rheology, and core evolution. By emphasizing the need for internal consistency among geochemical, geophysical, and geological constraints, this review provides a framework for evaluating mantle thermal evolution scenarios against independent global constraints.

The Hadean upper mantle may have been orthopyroxene-dominated, and constraining the rheology of this mineral is essential for understanding early Earth dynamics. Existing laboratory studies on orthopyroxene aggregates, however, were conducted under disparate pressure-temperature conditions, leaving the available dataset too sparse and fragmented to support reliable flow-law inversion, even with a Markov chain Monte Carlo approach. In this study, we develop a new, more direct formulation for estimating the effective viscosity of an orthopyroxene-rich mantle under Hadean conditions. Our formulation combines the limited experimental evidence with theoretical considerations of mantle convection, enabling extrapolation to planetary scales without requiring a statistically robust aggregate flow law. The results suggest that an orthopyroxene-dominated mantle could have been considerably weaker than a pyrolitic mantle, facilitating rapid plate motion during the Hadean.

Moon formation by a high-angular-momentum (high-AM) giant impact may be best able to explain Earth–Moon isotopic similarities. However, the excess AM must be subsequently removed for consistency with the Earth–Moon system. There are limited ways to achieve this. A leading mechanism is the evection resonance between the Earth, Moon, and Sun, which the early Moon would have encountered. It has been proposed that evection reduced the Earth–Moon angular momentum (AM) by a factor of >2, but this outcome is sensitive to the initial lunar orbit expansion rate, which was controlled by tidal dissipation in the Earth. Prior evection models adopt constant tidal parameters for the Earth. However, the Earth’s dissipative properties would have changed as its mantle cooled and solidified. Here, we model the Moon’s orbital evolution through evection, incorporating a physically motivated description for tidal dissipation in Earth following a high-AM impact. We present results for two limiting cases: one designed to isolate the variation in tidal dissipation due to Earth’s mantle cooling alone, while the other additionally includes inertial terms in the tidal deformation equations. The latter are important for the rapidly spinning initial Earth, and they produce a strongly enhanced, frequency-dependent dissipation. Using the full dissipation model, we find that evection resonance capture is sensitive to the Earth’s atmosphere properties and in all cases the Moon exits evection before enough AM is removed from the system. We conclude that it appears unlikely that the evection resonance alone can reconcile a high-AM Moon-forming impact with the present Earth–Moon system.

Terrestrial planets-Mercury, Venus, Earth and Mars-formed by the accretion of smaller objects. The Earth was probably the latest terrestrial planet to form and reached about 99% of its final mass within about 60-100 Myr after condensation of the first solids in the Solar System. This Review examines the disproportionate role of the last approximately 1% of planetary growth, or late accretion, in controlling the long-term evolution of the Earth and other terrestrial planets. Late accretion may have been responsible for shaping Earth's distinctive geophysical and chemical properties and generating pathways conducive to prebiotic chemistry. Differences in the late accretion of a planet may provide a rationale for interpreting the distinct properties of Venus and Earth (for example, tectonism, atmospheric composition, water content), the surface dichotomy of Mars and the high core-to-silicate mass ratio of Mercury. Large collisions and ensuing processes are likely to occur and modulate the evolution of rocky exoplanets as well, and they should be considered in our quest to find Earth-like worlds.

Tidal dissipation in a solidifying magma ocean is crucial for understanding the early thermal and orbital evolution of the Earth-Moon system. This study examines how matrix compaction affects tidal dissipation during magma ocean solidification. Using a one-dimensional two-phase flow model, we simulate the evolution of melt fraction profiles under various mantle potential temperatures and grain sizes. Whereas matrix compaction generally lowers tidal dissipation by reducing the cumulate thickness, our results show that, during early solidification phases, it can enhance dissipation at high tide-raising frequencies by increasing the resonance frequency of the magma ocean. These findings underscore the importance of considering matrix compaction in tidal dissipation models and suggest a potentially more complex interplay between solidification dynamics and tidal response than previously understood. This work provides a framework that allows us to better explore the possible evolutionary paths of the early Earth-Moon system.

The mode of tectonics that governed early Earth is controversial. This makes it challenging to infer surface environments relevant to the origin of life. The majority of the literature published in the past two decades was inclined to favor the appearance of plate tectonics sometime around the mid-Archean (∼3 Ga), with the operation of stagnant lid convection (or its variants) dominant in the earlier part of Earth's history. However, the available and increasing geological record from early Earth is actually equivocal, and there is no theoretical basis to prefer stagnant lid convection over plate tectonics. In fact, such a delayed onset of plate tectonics would inhibit the emergence of life in the Archean, let alone in the Hadean. On the contrary, rapid plate tectonics in the early Hadean, enabled by the fractional crystallization of a magma ocean, could quickly transform inclement young Earth into a habitable planet, with formation of multiple surface environments potentially conducive to abiogenesis.

Planetary formation involves highly energetic collisions, the consequences of which set the stage for the ensuing planetary evolution. During accretion, Earth's mantle was largely molten, a so‐called magma ocean, and its oxidation state was determined by equilibration with metal‐rich cores of infalling planetesimals through redox buffering reactions. We test two proposed mechanisms (metal layer and metal droplets) for equilibration in a magma ocean and the resulting oxidation state (Fe 3+ /ΣFe). Using scaling laws on convective mixing, we find that the metal layer could promote oxidation of a magma ocean, but this layer is too short‐lived to reproduce present‐day mantle Fe 3+ /ΣFe (2%–6%). Metal droplets produced by the fragmentation of impactor cores can also promote oxidation of a magma ocean. We use Monte Carlo sampling on two possible accretion scenarios to determine the likely range of oxidation states by metal droplets. We find that equilibration between silicate and metal droplets tends toward higher mantle Fe 3+ /ΣFe than presently observed. To achieve present‐day mantle Fe 3+ /ΣFe and maintain the degree of equilibration suggested by Hf‐W and U‐Pb systematics (30%–70%), the last (Moon‐forming) giant impact likely did not melt the entire mantle, therefore leaving the mantle stratified in terms of oxidation state after main accretion completes. Furthermore, late accretion impacts during the Hadean (4.5–4.0 Ga) could generate reduced domains in the shallow upper mantle, potentially sustaining surface environments conducive for prebiotic chemistry.

When modeling the early tidal evolution of the Earth-Moon system, we need to calculate tidal dissipation within Earth's solidifying magma ocean for a wide range of tide-raising frequency. This is because some giant impact hypotheses posit an initially rapidly spinning Earth. Also, the evection resonance, which is likely to have been encountered by the early Earth-Moon system, increases lunar orbital eccentricity, which can broaden the frequency range. It is shown that the standard solution methods such as the propagator matrix method and the shooting method are insufficient to handle this wide range of frequency. As tide-raising frequency increases, the effect of inertia becomes significant, but the propagator matrix method is commonly implemented only with the governing equations without inertia. The shooting method can handle high frequencies well, but it becomes unbearably unstable toward the low frequency end. The relaxation method is found to be extremely stable over the entire frequency range considered, being able to handle huge viscosity variations over 20 orders of magnitudes. For an initially rapidly spinning Earth, the effects of inertia and lunar orbital eccentricity are considerable, warranting a careful reevaluation of various scenarios for the early lunar evolution.

As a means of geological carbon sequestration, in-situ mineral carbonation has enormous potential, owing to the sheer magnitude of potentially accessible mafic and ultramafic reservoirs. Because carbonation is a solid-volume-increasing reaction, however, the effective exploitation of such subsurface reservoirs depends critically on the efficacy of reaction-driven cracking, which in turn rests on still elusive estimates of crystallization pressure in geological materials. Here we show that, by relating porosity generation with carbonation reaction through elastic strain energy, the maximum degree of in-situ carbonation in the limit of zero crystallization pressure can be expressed as a simple function of the confining pressure, the tensile strength of rocks, the initial porosity, and the relative solid-volume change. This theoretical estimate will help us better interpret laboratory experiments and integrate them with field-scale studies to assess the storage potential of various geological reservoirs under different conditions.

The ocean pH is a fundamental property regulating various aspects of Earth system evolution. However, the early ocean pH remains controversial, with estimates ranging from strongly acidic to alkaline. Here we develop a model integrating global carbon cycling with ocean geochemistry, and incorporating continental growth and mantle thermal evolution. By coupling global carbon cycle with ocean charge balance, and by using solid Earth processes of mantle degassing and crustal evolution to specify the history of volatile distribution and ocean chemistry, we show that a rapid increase in ocean pH is likely during the Hadean to the early Archean, with pH evolving from 5 to neutral by approximately 4.0 Ga. This rapid pH evolution is attributed primarily to elevated rates of both seafloor and continental weathering during the Hadean. This acceleration in weathering rates originates in the unique aspects of Hadean geodynamics, including rapid crust formation, different crustal lithology, and fast plate motion. Earth likely transformed from a hostile state to a habitable one by the end of the Hadean, approximately 4.0 Ga, with important implications for planetary habitability and the origin of life.

As an important reservoir for incompatible elements, the growth of the continental crust profoundly influenced the composition of the mantle and the atmosphere. The co-evolution of the continental crust, mantle, and atmosphere throughout Earth history can be traced through the transfer of argon and potassium between these three reservoirs. While many argon-constrained crustal growth models have been proposed, none of them consider the effect of late accretion (bombardment by leftover planetesimals in the several hundred million years after the Moon formed) in detail. Our model is the first of its kind to simulate both the volatile delivery and the atmospheric erosion by impacting planetesimals. Whereas the relative fraction of impactor-derived argon in the present-day atmosphere depends on the assumed impactor composition and the starting atmospheric mass, the present-day atmospheric argon originates largely from mantle degassing and crustal processing. For a range of impact parameters, our model results indicate that the early rapid growth of continental crust is required to satisfy the argon budget of the mantle and atmosphere.

The oceanic mantle lithosphere has considerable potential to store chemically bound water, thereby being an important factor for the deep water cycle. However, the actual extent of hydrous alteration in such mantle rocks is debated. Geodynamic modeling has the potential to directly predict the extent of fluid flow through oceanic lithosphere, and, in turn, the extent of serpentinization. By comparing theory and numerical simulations, we demonstrate that conventional geodynamic models are inherently inconsistent with the physics of brittle deformation, and, as a result, they overestimate the extent of fluid flow during extension. In contrast to the extensive serpentinization often inferred with bending-related processes during subduction, limited serpentinization is consistent with theoretical predictions and geophysical observations.

The early orbital evolution of the Earth-Moon system is strongly coupled with the thermal evolution of Earth's magma ocean formed after the Moon-forming giant impact. The thermal budget of the magma ocean is dominated by the balance between tidal heating and the surface heat flux of the magma ocean. The former is effectively limited by the latter, because the magma ocean would stop cooling as soon as tidal heating is large enough to match the surface heat flux. One of the key factors controlling the magma ocean surface heat flux is the temperature difference at the surface, which is regulated by the thermal structure of the coexisting atmosphere. To evaluate the impact of tidal dissipation on the evolution of the Earth-Moon system, therefore, it becomes essential to understand how the cooling efficiency of Earth's magma ocean is regulated by the thermal blanketing effect of the coexisting atmosphere, which is in turn affected by the degassing history of the magma ocean. In this work, we couple a comprehensive atmospheric model with a realistic mantle phase diagram to quantify how the surface heat flux from a magma ocean would change during the course of its solidification. Our results show that gray and nongray treatments result in about one order of magnitude difference in heat flux and that likely uncertainties in Earth's volatile budget as well as degassing efficiency have a limited influence on magma ocean heat flux. Most importantly, the magnitude of tidal heating can be comparable to or even greater than magma ocean heat flux for a range of early Earth conditions, highlighting the fundamental role of atmospheric blanketing in the tidal evolution of the Earth-Moon system.

Ocean pH is a fundamental property regulating various aspects of Earth system evolution. However, early ocean pH remains controversial, with estimates ranging from strongly acidic to alkaline. Here we develop a model integrating global carbon cycling with ocean geochemistry, and incorporating continental growth and mantle thermal evolution. By coupling global carbon cycle with ocean charge balance, and by using solid Earth processes of mantle degassing and crustal evolution to specify the history of volatile distribution and ocean chemistry, we show that a rapid increase in ocean pH is likely during the Hadean to the early Archaean eons, with pH evolving from 5 to neutral by approximately 4.0 Gyr ago. This rapid pH evolution is attributed primarily to elevated rates of both seafloor and continental weathering during the Hadean. This acceleration in weathering rates originates in the unique aspects of Hadean geodynamics, including rapid crust formation, different crustal lithology and fast plate motion. Earth probably transformed from a hostile state to a habitable one by the end of the Hadean, approximately 4.0 Gyr ago, with important implications for planetary habitability and the origin of life.

It has been suggested that Earth's present water budget formed from oxidation reactions between its initial hydrogen-rich primordial atmosphere and its magma ocean. Here we examine this hypothesis by building a comprehensive atmosphere-magma ocean model. We find that water formation is unlikely for two reasons. First, any water formed from oxidation reactions in the magma ocean would quickly outgas because of the water-poor atmosphere above. Second, the top boundary layer of the magma ocean becomes stable against convection because the oxidation reactions produce metallic iron, which sinks to the core of a growing Earth. This iron loss makes the top boundary layer significantly more buoyant than the rest of the magma, thus becoming stable against mixing. Our results suggest that hydrogen dissolution is unlikely to play a major role in the formation of Earth's oceans.