Annual Review of Earth and Planetary Sciences - Volume 51, 2023

I describe my career journey from a young girl in Cameroon, West Africa, to a trailblazing geophysicist to my current role as dean. I chronicle my time as a student, the transition to being an early career faculty, launching my research career, and ultimately finding my way to administration. Along the way I helped pioneer biogeophysics as a subdiscipline in geophysics while simultaneously maintaining an international research program in continental rift tectonics. I also describe the many intersectionalities in my life including being the first Black woman in many spaces, being a champion for student success, developing a diverse talent pipeline by enhancing diversity in the geosciences, and navigating academic job searches as part of a dual-career couple. Finally, I acknowledge all those who helped shape my career including the many students I had the opportunity to mentor.

• ▪  Many underrepresented minority geoscientists lack the social capital and professional networks critical for their success.
• ▪  Geoscience departments must be intentional and deliberate in promoting and ensuring more inclusive workplace environments.
• ▪  Dual-career couples remain a major challenge, impacting retention and recruitment of top talent; universities should provide resources to alleviate this challenge.
• ▪  Biogeophysics has untapped potential for advancing understanding of subsurface biogeochemical processes and the search for life in extreme environments.
• ▪  To date, considerable speculation remains regarding the fundamental geodynamic processes that initiate and sustain the evolution of magma-deficient rifts.

Defining the age of the Moon has proven to be an elusive task because it requires reliably dating lunar samples using radiometric isotopic systems that record fractionation of parent and daughter elements during events that are petrologically associated with planet formation. Crystallization of the magma ocean is the only event that unambiguously meets this criterion because it probably occurred within tens of millions of years of Moon formation. There are three dateable crystallization products of the magma ocean: mafic mantle cumulates, felsic crustal cumulates, and late-stage crystallization products known as urKREEP (uniform residuum K, rare earth elements, and P). Although ages for these materials in the literature span 200 million years, there is a preponderance of reliable ages around 4.35 billion years recorded in all three lunar rock types. This age is also observed in many secondary crustal rocks, indicating that they were produced contemporaneously (within uncertainty of the ages), possibly during crystallization and overturn of the magma ocean.

• ▪  The duration of planet formation is key information in understanding the mechanisms by which the terrestrial planets formed.
• ▪  Ages of the oldest lunar rocks range widely, reflecting either the duration of Moon formation or disturbed ages caused by impact metamorphism.
• ▪  Ages determined for compositionally distinct crust and mantle materials produced by lunar magma ocean differentiation cluster near 4.35 Gyr.
• ▪  The repeated occurrence of 4.35 Gyr ages implies that Moon formation occurred late in Solar System history, likely by giant impact into Earth.

A science-based understanding of climate change and potential mitigation and adaptation options can provide decision makers with important guidance in making decisions about how best to respond to the many challenges inherent in climate change. In this review we provide an evidence-based heuristic for guiding efforts to share science-based information about climate change with decision makers and the public at large. Well-informed decision makers are likely to make better decisions, but for a range of reasons, their inclinations to act on their decisions are not always realized into effective actions. We therefore also provide a second evidence-based heuristic for helping people and organizations change their climate change–relevant behaviors, should they decide to. These two guiding heuristics can help scientists and others harness the power of communication and behavior science in service of enhancing society's response to climate change.

• ▪  Many Earth scientists seeking to contribute to the climate science translation process feel frustrated by the inadequacy of the societal response.
• ▪  Here we summarize the social science literature by offering two guiding principles to guide communication and behavior change efforts.
• ▪  To improve public understanding, we recommend simple, clear messages, repeated often, by a variety of trusted and caring messengers.
• ▪  To encourage uptake of useful behaviors, we recommend making the behaviors easy, fun, and popular.

Future sea-level rise poses an existential threat for many river deltas, yet quantifying the effect of sea-level changes on these coastal landforms remains a challenge. Sea-level changes have been slow compared to other coastal processes during the instrumental record, such that our knowledge comes primarily from models, experiments, and the geologic record. Here we review the current state of science on river delta response to sea-level change, including models and observations from the Holocene until 2300 CE. We report on improvements in the detection and modeling of past and future regional sea-level change, including a better understanding of the underlying processes and sources of uncertainty. We also see significant improvements in morphodynamic delta models. Still, substantial uncertainties remain, notably on present and future subsidence rates in and near deltas. Observations of delta submergence and land loss due to modern sea-level rise also remain elusive, posing major challenges to model validation.

• ▪  There are large differences in the initiation time and subsequent delta progradation during the Holocene, likely from different sea-level and sediment supply histories.
• ▪  Modern deltas are larger and will face faster sea-level rise than during their Holocene growth, making them susceptible to forced transgression.
• ▪  Regional sea-level projections have been much improved in the past decade and now also isolate dominant sources of uncertainty, such as the Antarctic ice sheet.
• ▪  Vertical land motion in deltas can be the dominant source of relative sea-level change and the dominant source of uncertainty; limited observations complicate projections.
• ▪  River deltas globally might lose 5% (∼35,000 km²) of their surface area by 2100 and 50% by 2300 due to relative sea-level rise under a high-emission scenario.

Machine learning (ML) is a collection of methods used to develop understanding and predictive capability by learning relationships embedded in data. ML methods are becoming the dominant approaches for many tasks in seismology. ML and data mining techniques can significantly improve our capability for seismic data processing. In this review we provide a comprehensive overview of ML applications in earthquake seismology, discuss progress and challenges, and offer suggestions for future work.

• ▪  Conceptual, algorithmic, and computational advances have enabled rapid progress in the development of machine learning approaches to earthquake seismology.
• ▪  The impact of that progress is most clearly evident in earthquake monitoring and is leading to a new generation of much more comprehensive earthquake catalogs.
• ▪  Application of unsupervised approaches for exploratory analysis of these high-dimensional catalogs may reveal new understanding of seismicity.
• ▪  Machine learning methods are proving to be effective across a broad range of other seismological tasks, but systematic benchmarking through open source frameworks and benchmark data sets are important to ensure continuing progress.

Volcanic eruptions are driven by bubbles that form when volatile species exsolve from magma. The conditions under which bubbles form depend mainly on magma composition, volatile concentration, presence of crystals, and magma decompression rate. These are all predicated on the mechanism by which volatiles exsolve from the melt to form bubbles. We critically review the known or inferred mechanisms of bubble formation in magmas: homogeneous nucleation, heterogeneous nucleation on crystal surfaces, and spontaneous phase separation (spinodal decomposition). We propose a general approach for calculating bubble nucleation rates as the sum of the contributions from homogeneous and heterogeneous nucleation, suggesting that nucleation may not be limited to a single mechanism prior to eruption. We identify three major challenges in which further experimental, analytical, and theoretical work is required to permit the development of a general model for bubble formation under natural eruption conditions.

• ▪  We review the mechanisms of bubble formation in magma and summarize the conditions under which the various mechanisms are understood to operate.
• ▪  Bubble formation mechanisms may evolve throughout magma ascent as conditions change such that bubbles may form simultaneously and sequentially via more than one mechanism.
• ▪  Contributions from both homogeneous nucleation and heterogeneous nucleation on multiphase crystal phases can be captured via a single equation.
• ▪  Future work should focus on constraining macroscopic surface tension, characterizing the microphysics, and developing a general framework for modeling bubble formation, via all mechanisms, over natural magma ascent pathways.

The continental crust in the overriding plate of the India-Asia collision zone in southern Tibet is characterized by an overthickened layer of felsic composition with an underlying granulite-eclogite layer. A large data set indicates that this crust experienced magmatism from 245 to 10 Ma, as recorded by the Gangdese Batholith. Magmatism was punctuated by flare-ups at 185−170, 90−75, and 55−45 Ma caused by a combination of external and internal factors. The growth of this crust starts with a period dominated by fractional crystallization and the formation of voluminous (ultra)mafic arc cumulates in the lower crust during subduction, followed by their melting during late-subduction and collision, due to changes in convergence rate. This combined accumulation-melting process resulted in the vertical stratification and density sorting of the Gangdese crust. Comparisons with other similarly thickened collision zones suggests that this is a general process that leads to the stabilization of continental crust.

• ▪  The Gangdese Batholith records the time-integrated development of the world's thickest crust, reaching greater than 50 km at 55–45 Ma and greater than 70 km after 32 Ma.
• ▪  The Gangdese Batholith records three magmatic flare-ups in response to distinct drivers; the last one at 55−45 Ma marks the arrival of India.
• ▪  Magmatism was first dominated by fractional crystallization (accumulation) followed by crustal melting: the accumulation-melting process.
• ▪  Accumulation-melting in other collision zones provides a general process for vertical stratification and stabilization of continental crust.

Uncertainty about sea-level rise is dominated by uncertainty about iceberg calving, mass loss from glaciers or ice sheets by fracturing. Review of the rapidly growing calving literature leads to a few overarching hypotheses. Almost all calving occurs near or just downglacier of a location where ice flows into an environment more favorable for calving, so the calving rate is controlled primarily by flow to the ice margin rather than by fracturing. Calving can be classified into five regimes, which tend to be persistent, predictable, and insensitive to small perturbations in flow velocity, ice characteristics, or environmental forcing; these regimes can be studied instrumentally. Sufficiently large perturbations may cause sometimes-rapid transitions between regimes or between calving and noncalving behavior, during which fracturing may control the rate of calving. Regime transitions underlie the largest uncertainties in sea-level rise projections, but with few, important exceptions, have not been observed instrumentally. This is especially true of the most important regime transitions for sea-level rise. Process-based models informed by studies of ongoing calving, and assimilation of deep-time paleoclimatic data, may help reduce uncertainties about regime transitions. Failure to include calving accurately in predictive models could lead to large underestimates of warming-induced sea-level rise.

• ▪  Iceberg calving, the breakage of ice from glaciers and ice sheets, affects sea level and many other environmental issues.
• ▪  Modern rates of iceberg calving usually are controlled by the rate of ice flow past restraining points, not by the brittle calving processes.
• ▪  Calving can be classified into five regimes, which are persistent, predictable, and insensitive to small perturbations.
• ▪  Transitions between calving regimes are especially important, and with warming might cause faster sea-level rise than generally projected.

Large seismogenic faults consist of approximately meter-thick fault cores surrounded by hundreds-of-meters-thick damage zones. Earthquakes are generated by rupture propagation and slip within fault cores and dissipate the stored elastic strain energy in fracture and frictional processes in the fault zone and in radiated seismic waves. Understanding this energy partitioning is fundamental in earthquake mechanics to explain fault dynamic weakening and causative rupture processes operating over different spatial and temporal scales. The energy dissipated in the earthquake rupture propagation along a fault is called fracture energy or breakdown work. Here we review fracture energy estimates from seismological, modeling, geological, and experimental studies and show that fracture energy scales with fault slip. We conclude that although material-dependent constant fracture energies are important at the microscale for fracturing grains of the fault zone, they are negligible with respect to the macroscale processes governing rupture propagation on natural faults.

• ▪  Earthquake ruptures propagate on geological faults and dissipate energy in fracture and frictional processes from micro- (less than a millimeter) to macroscale (centimeters to kilometers).

• ▪  The energy dissipated in earthquake rupture propagation is called fracture energy (G) or breakdown work (Wb) and scales with coseismic slip.
• ▪  For earthquake ruptures in natural faults, the estimates of G and Wb are consistent with a macroscale description of causative processes.
• ▪  The energy budget of an earthquake remains controversial, and contributions from different disciplines are required to unravel this issue.

An oxygen-rich atmosphere is essential for complex animals. The early Earth had an anoxic atmosphere, and understanding the rise and maintenance of high O2 levels is critical for investigating what drove our own evolution and for assessing the likely habitability of exoplanets. A growing number of techniques aim to reproduce changes in O2 levels over the Phanerozoic Eon (the past 539 million years). We assess these methods and attempt to draw the reliable techniques together to form a consensus Phanerozoic O2 curve. We conclude that O2 probably made up around 5–10% of the atmosphere during the Cambrian and rose in pulses to ∼15–20% in the Devonian, reaching a further peak of greater than 25% in the Permo-Carboniferous before declining toward the present day. Evolutionary radiations in the Cambrian and Ordovician appear consistent with an oxygen driver, and the Devonian “Age of the Fishes” coincides with oxygen rising above 15% atm.

• ▪  An oxygen-rich atmosphere is essential for complex animals such as humans.
• ▪  We review the methods for reconstructing past variation in oxygen levels over the past 539 million years (the Phanerozoic Eon).
• ▪  We produce a consensus plot of the most likely evolution of atmospheric oxygen levels.
• ▪  Evolutionary radiations in the Cambrian, Ordovician, and Devonian periods may be linked to rises in oxygen concentration.

Landscapes receive water from precipitation and then transport, store, mix, and release it, both downward to streams and upward to vegetation. How they do this shapes floods, droughts, biogeochemical cycles, contaminant transport, and the health of terrestrial and aquatic ecosystems. Because many of the key processes occur invisibly in the subsurface, our conceptualization of them has often relied heavily on physical intuition. In recent decades, however, much of this intuition has been overthrown by field observations and emerging measurement methods, particularly involving isotopic tracers. Here we summarize key surprises that have transformed our understanding of hydrological processes at the scale of hillslopes and drainage basins. These surprises have forced a shift in perspective from process conceptualizations that are relatively static, homogeneous, linear, and stationary to ones that are predominantly dynamic, heterogeneous, nonlinear, and nonstationary.

• ▪  Surprising observations and novel measurements are transforming our understanding of the hydrological functioning of landscapes.
• ▪  Even during storm peaks, streamflow is composed mostly of water that has been stored in the landscape for weeks, months, or years.
• ▪  Streamflow and tree water uptake often originate from different subsurface storages and from different seasons’ precipitation.
• ▪  Stream networks dynamically extend and retract as the landscape wets and dries, and many stream reaches lose flow into underlying aquifers.

The early to mid-Paleoproterozoic Lomagundi-Jatuli Excursion (LJE) is ostensibly the largest magnitude (approximately +5 to +30‰), longest duration (ca. 130–250 million years) positive carbon isotope excursion measured in carbonate rocks in Earth history. The LJE has been attributed to large nutrient fluxes, an increase in the size of the biosphere, a reorganization of the global carbon cycle, and oxygenation of the atmosphere. However, significant debate remains about its genesis, synchroneity, global-versus-local extent, and role in atmospheric oxygenation. Here we review existing models and mechanisms suggested for the LJE and analyze a compilation of ∼9,400 δ¹³Ccarb and associated contextual data. These data call into question the interpretation of the LJE as a globally synchronous carbon isotope excursion and suggest that any model for the LJE must account for both the absence of a clearly defined initiation and termination of the excursion and a facies-dependent expression of ¹³C-enrichment.

• ▪  The Lomagundi-Jatuli Excursion (LJE) continues to challenge current understandings of the carbon cycle.
• ▪  Understanding this excursion is critical for reconstructing biogeochemical cycles and atmospheric oxygenation through Earth history.
• ▪  Some evidence indicates local rather than global changes in δ¹³CDIC and raises the possibility of asynchronous, local excursions.
• ▪  Resolving whether the LJE was globally synchronous or asynchronous is essential for discriminating between different models.

Upon exhumation and cooling, contrasting compressibilities and thermal expansivities induce differential strains (volume mismatches) between a host crystal and its inclusions. These strains can be quantified in situ using Raman spectroscopy or X-ray diffraction. Knowing equations of state and elastic properties of minerals, elastic thermobarometry inverts measured strains to calculate the pressure-temperature conditions under which the stress state was uniform in the host and inclusion. These are commonly interpreted to represent the conditions of inclusion entrapment. Modeling and experiments quantify corrections for inclusion shape, proximity to surfaces, and (most importantly) crystal-axis anisotropy, and they permit accurate application of the more common elastic thermobarometers. New research is exploring the conditions of crystal growth, reaction overstepping, and the magnitudes of differential stresses, as well as inelastic resetting of inclusion and host strain, and potential new thermobarometers for lower-symmetry minerals.

• ▪  A physics-based method is revolutionizing calculations of metamorphic pressures and temperatures.
• ▪  Inclusion shape, crystal anisotropy, and proximity to boundaries affect calculations but can be corrected for.
• ▪  New results are leading petrologists to reconsider pressure-temperature conditions, differential stresses, and thermodynamic equilibrium.

Mimas, the smallest and innermost of Saturn's mid-sized moons, has a heavily cratered surface devoid of the intricate fracture systems of its neighbor, Enceladus. However, Cassini measurements identified a signature of an ocean under Mimas’ ice shell, although a frozen ice shell over a rocky interior could not be ruled out. The Mimas ocean hypothesis has stimulated inquiry into Mimas’ geologic history and orbital evolution. Here, we summarize the results of these investigations, which (perhaps surprisingly) are consistent with an ocean-bearing Mimas as long as it is geologically young. In that case, a ring origin for Mimas is favored over primordial accretion. An independently developed model for the formation of a gap in Saturn's rings provides a potential mechanism for generating a late-stage ocean within Mimas and may have assisted in the development of Enceladus’ ocean and associated geologic activity. Rather than a battered relic, Mimas may be the youngest ocean moon in the Saturn system, destined to join Enceladus as an active world in the future. The presence of oceans within Saturn's mid-sized moons also has implications for the habitability of Uranus’ moons; the Uranus system was chosen as the highest priority target for the next NASA Flagship-class mission.

• ▪  Models of Mimas’ tides and rotation state support a present-day internal ocean.
• ▪  Mimas’ craters, impact basin, and lack of widespread tectonism are compatible with a stable/warming ocean.
• ▪  The formation of the Cassini Division within Saturn's rings provides a potential pathway to a present-day ocean within Mimas.
• ▪  If Mimas has an ocean today, it is geologically young.

The timing of ice ages over the past ∼2,600 thousand years (kyr) follows pacing by cyclical changes in three aspects of Earth's orbit that influence the solar energy received as a function of latitude and season. Explaining the large magnitude of the climate changes is challenging, particularly so across the period of time from ∼1,250 to 750 ka—the Mid-Pleistocene Transition or MPT. The average repeat time of ice age cycles changed from an earlier 41-kyr rhythm to longer and more intense glaciations at a spacing of about 100 kyr. Explaining this change is very difficult because there was no corresponding change in the orbital pacing that would trigger a change in timing. While the first generation of hypotheses looked largely to changes in the behavior of Northern Hemisphere ice sheets, more recent work integrates ice behavior with new data capturing the evolution of other important aspects of past climate. A full explanation is still lacking, but attention increasingly focuses on the ocean carbon cycle and atmospheric CO2 levels as the crucial agents involved in the MPT.

• ▪  The pattern of climate changes connected to the ice ages of the past few million years changed radically between about 1,250 and 750 thousand years ago, a time known as the Mid-Pleistocene Transition or MPT.
• ▪  While the glacial cycles were ultimately triggered by cyclical changes in Earth's orbit, the changes across the MPT came from changes in the Earth system itself, most likely in the form of a change in the carbon cycle.
• ▪  The dramatic change in many essential aspects of climate—ice volume, temperature, rainfall on land, and many others—in the absence of an external change suggests how important feedbacks are to the climate system.

The Amazon hosts one of the largest and richest rainforests in the world, but its origins remain debated. Growing evidence suggests that geodiversity and geological history played essential roles in shaping the Amazonian flora. Here we summarize the geo-climatic history of the Amazon and review paleopalynological records and time-calibrated phylogenies to evaluate the response of plants to environmental change. The Neogene fossil record suggests major sequential changes in plant composition and an overall decline in diversity. Phylogenies of eight Amazonian plant clades paint a mixed picture, with the diversification of most groups best explained by constant speciation rates through time, while others indicate clade-specific increases or decreases correlated with climatic cooling or increasing Andean elevation. Overall, the Amazon forest seems to represent a museum of diversity with a high potential for biological diversification through time. To fully understand how the Amazon got its modern biodiversity, further multidisciplinary studies conducted within a multimillion-year perspective are needed.

• ▪  The history of the Amazon rainforest goes back to the beginning of the Cenozoic (66 Ma) and was driven by climate and geological forces.
• ▪  In the early Neogene (23–13.8 Ma), a large wetland developed with episodic estuarine conditions and vegetation ranging from mangroves to terra firme forest.
• ▪  In the late Neogene (13.8–2.6 Ma), the Amazon changed into a fluvial landscape with a less diverse and more open forest, although the details of this transition remain to be resolved.
• ▪  These geo-climatic changes have left imprints on the modern Amazonian diversity that can be recovered with dated phylogenetic trees.
• ▪  Amazonian plant groups show distinct responses to environmental changes, suggesting that Amazonia is both a refuge and a cradle of biodiversity.

As atmospheric carbon dioxide concentrations rise and climate change becomes more destructive, geoengineering has become a subject of serious consideration. By reflecting a fraction of incoming sunlight, solar geoengineering could cool the planet quickly, but with uncertain effects on regional climatology, particularly hydrological patterns. Here, we review recent work on projected hydrologic outcomes of solar geoengineering, in the context of a robust literature on hydrological responses to climate change. While most approaches to solar geoengineering are expected to weaken the global hydrologic cycle, regional effects will vary based on implementation method and strategy. The literature on the hydrologic outcomes and impacts of geoengineering demonstrates that its implications for human welfare will depend on assumptions about underlying social conditions and objectives of intervention as well as the social lens through which projected effects are interpreted. We conclude with suggestions to reduce decision-relevant uncertainties in this novel field of Earth science inquiry.

• ▪  The expected hydrological effects of reducing insolation are among the most uncertain and consequential impacts of solar geoengineering (SG).
• ▪  Theoretical frameworks from broader climate science can help explain SG's effects on global precipitation, relative humidity, and other aspects of hydroclimate.
• ▪  The state of the knowledge on hydrological impacts of SG is unevenly concentrated among regions.
• ▪  Projected hydrological impacts from SG are scenario dependent and difficult to characterize as either harmful or beneficial.

The current rapid increase in atmospheric CO2, linked to the massive use of fossil fuels, will have major consequences for our climate and for living organisms. To understand what is happening today, it is informative to look at the past. The evolution of the carbon cycle, coupled with that of the past climate system and the other coupled elemental cycles, is explored in the field, in the laboratory, and with the help of numerical modeling. The objective of numerical modeling is to be able to provide a quantification of the processes at work on our planet. Of course, we must remain aware that a numerical model, however complex, will never include all the relevant processes, impacts, and consequences because nature is complex and not all the processes are known. This makes models uncertain. We are still at the beginning of the exploration of the deep-time Earth. In the present contribution, we review some crucial events in coupled Earth-climate-biosphere evolution over the past 540 million years, focusing on the models that have been developed and what their results suggest. For most of these events, the causes are complex and we are not able to conclusively pinpoint all causal relationships and feedbacks in the Earth system. This remains a largely open scientific field.

• ▪  The era of the pioneers of geological carbon cycle modeling is coming to an end with the recent development of numerical models simulating the physics of the processes, including climate and the role of vegetation, while taking into account spatialization.
• ▪  Numerical models now allow us to address increasingly complex processes, which suggests the possibility of simulating the complete carbon balance of objects as complex as a mountain range.
• ▪  While most of the processes simulated by models are physical-chemical processes in which the role of living organisms is taken into account in a very simple way, via a limited number of parameters, models of the carbon cycle in deep time coupled with increasingly complex ecological models are emerging and are profoundly modifying our understanding of the evolution of our planet's surface.
  
  

Our understanding of Earth's rock-hosted subsurface biosphere has advanced over the past two decades through the collection and analysis of fluids and rocks from aquifers within the continental and oceanic crust. Improvements in cell extraction, cell sorting, DNA sequencing, and techniques for detecting cell distributions and activity have revealed how the combination of lithology, permeability, and fluid mixing processes controls the diversity and heterogeneous distribution of microbial communities in fractured rock systems. However, the functions of most organisms, and the rates of their activity and growth, remain largely unknown. To mechanistically understand what physiochemical and hydrological factors control the rock-hosted biosphere, future studies are needed to characterize the physiology of microorganisms adapted to mineral-associated growth under energy- and nutrient-limited conditions. Experiments should be designed to detect synergistic interactions between microorganisms, and between microorganisms and minerals, at highly variable turnover rates.

• ▪  The heterogeneous distribution of the rock-hosted biosphere is controlled by variations in porosity, permeability, and chemical disequilibrium.
• ▪  Several imaging and chemical techniques can sensitively detect microbial activity within the rock-hosted biosphere.
• ▪  The physiology and turnover rates of the subsurface rock-hosted biosphere remain poorly known.

Kimberlite-borne xenolithic eclogites, typically occurring in or near cratons, have long been recognized as remnants of Precambrian subducted oceanic crust that have undergone partial melting to yield granitoids similar to the Archean continental crust. While some eclogitized oceanic crust was emplaced into cratonic lithospheres, the majority was deeply subducted to form lithologic and geochemical heterogeneities in the convecting mantle. If we accept that most xenolithic eclogites originally formed at Earth's surface, then their geodynamic significance encompasses four tectonic environments: (a) spreading ridges, where precursors formed by partial melting of convecting mantle and subsequent melt differentiation; (b) subduction zones, where oceanic crust was metamorphosed and interacted with other slab lithologies; (c) the cratonic mantle lithosphere, where the eclogite source was variably modified subsequent to emplacement in Mesoarchean to Paleoproterozoic time; and (d) the convecting mantle, into which the vast majority of subduction-modified oceanic crust not captured in the cratonic lithosphere was recycled.

• ▪  Xenolithic eclogites are fragments of ca. 3.0–1.8 Ga oceanic crust and signal robust subduction tectonics from the Mesoarchean.
• ▪  Multiple constraints indicate an origin as variably differentiated oceanic crust, followed by subduction metamorphism, and prolonged mantle residence.

• ▪  Xenolithic eclogites thus permit investigation of deep geochemical cycles related to recycling of Precambrian oceanic crust.
• ▪  They help constrain asthenosphere thermal plus redox evolution and contribute to cratonic physical properties and mineral endowments.

Terrestrial plants have transformed Earth's surface environments by altering water, energy, and biogeochemical cycles. Studying vegetation-climate interaction in deep time has necessarily relied on modern-plant analogs to represent paleo-ecosystems—as methods for reconstructing paleo- and, in particular, extinct-plant function were lacking. This approach is potentially compromised given that plant physiology has evolved through time, and some paleo-plants have no clear modern analog. Advancements in the quantitative reconstruction of whole-plant function provide new opportunities to replace modern-plant analogs and capture age-specific vegetation-climate interactions. Here, we review recent investigations of paleo-plant performance through the integration of fossil and geologic data with process-based ecosystem- to Earth system–scale models to explore how early vascular plants responded to and influenced climate. First, we present an argument for characterizing extinct plants in terms of ecological and evolutionary theory to provide a framework for advancing reconstructed vegetation-climate interactions in deep time. We discuss the novel mechanistic understanding provided by applying these approaches to plants of the late Paleozoic ever-wet tropics and at higher latitudes. Finally, we discuss preliminary applications to paleo-plants in a state-of-the-art Earth system model to highlight the potential implications of different plant functional strategies on our understanding of vegetation-climate interactions in deep time.

• ▪  For hundreds of millions of years, plants have been a keystone in maintaining the status of Earth's atmosphere, oceans, and climate.
• ▪  Extinct plants have functioned differently across time, limiting our understanding of how processes on Earth interact to produce climate.
• ▪  New methods, reviewed here, allow quantitative reconstruction of extinct-plant function based on the fossil record.
• ▪  Integrating extinct plants into ecosystem and climate models will expand our understanding of vegetation's role in past environmental change.

The strength of lithospheric plates is a central component of plate tectonics, governed by brittle processes in the shallow portion of the plate and ductile behavior in the deeper portion. We review experimental constraints on ductile deformation of olivine, the main mineral in the upper mantle and thus the lithosphere. Olivine deforms by four major mechanisms: low-temperature plasticity, dislocation creep, dislocation-accommodated grain-boundary sliding (GBS), and diffusion-accommodated grain-boundary sliding (diffusion creep). Deformation in most of the lithosphere is dominated by GBS, except in shear zones—in which diffusion creep dominates—and in the brittle-ductile transition—in which low-temperature plasticity may dominate. We find that observations from naturally deformed rocks are consistent with extrapolation of the experimentally constrained olivine flow laws to geological conditions but that geophysical observations predict a weaker lithosphere. The causes of this discrepancy are unresolved but likely reside in the uncertainty surrounding processes in the brittle-ductile transition, at which the lithosphere is strongest.

• ▪  Ductile deformation of the lithospheric mantle is constrained by experimental data for olivine.
• ▪  Olivine deforms by four major mechanisms: low-temperature plasticity, dislocation creep, dislocation-accommodated grain-boundary sliding, and diffusion creep.
• ▪  Observations of naturally deformed rocks are consistent with extrapolation of olivine flow laws from experimental conditions.
• ▪  Experiments predict stronger lithosphere than geophysical observations, likely due to gaps in constraints on deformation in the brittle-ductile transition.

Carbonate minerals contain stable isotopes of carbon and oxygen with different masses whose abundances and bond arrangement are governed by thermodynamics. The clumped isotopic value Δi is a measure of the temperature-dependent preference of heavy C and O isotopes to clump, or bond with or near each other, rather than with light isotopes in the carbonate phase. Carbonate clumped isotope thermometry uses Δi values measured by mass spectrometry (Δ47, Δ48) or laser spectroscopy (Δ638) to reconstruct mineral growth temperature in surface and subsurface environments independent of parent water isotopic composition. Two decades of analytical and theoretical development have produced a mature temperature proxy that can estimate carbonate formation temperatures from 0.5 to 1,100°C, with up to 1–2°C external precision (2 standard error of the mean). Alteration of primary environmental temperatures by fluid-mediated and solid-state reactions and/or Δi values that reflect nonequilibrium isotopic fractionations reveal diagenetic history and/or mineralization processes. Carbonate clumped isotope thermometry has contributed significantly to geological and biological sciences, and it is poised to advance understanding of Earth's climate system, crustal processes, and growth environments of carbonate minerals.

• ▪  Clumped heavy isotopes in carbonate minerals record robust temperatures and fluid compositions of ancient Earth surface and subsurface environments.
• ▪  Mature analytical methods enable carbonate clumped Δ47, Δ48, and Δ638 measurements to address diverse questions in geological and biological sciences.
• ▪  These methods are poised to advance marine and terrestrial paleoenvironment and paleoclimate, tectonics, deformation, hydrothermal, and mineralization studies.

For the first time, from early 2019 to the end of 2022, Mars’ shallow and deep interiors have been explored by seismology with the InSight mission. Thanks to the performances of its seismometers and the quality of their robotic installation on the ground, 1,319 seismic events have been detected, including about 90 marsquakes at teleseismic distances, with Mw from 2.5 to 4.7 and at least 6 impacts, the largest ones with craters larger than 130 m. A large fraction of these marsquakes occur in Cerberus Fossae, demonstrating active regional tectonics. Records of pressure-induced seismic noise and signals from the penetration of a heat flow probe have provided subsurface models below the lander. Deeper direct and secondary body wave phase travel time, receiver function, and surface wave analysis have provided the first interior models of Mars, including crustal thickness and crustal layering, mantle structure, thermal lithospheric thickness, and core radius and state.

• ▪  With InSight's SEIS (Seismic Experiment for Interior Structure of Mars) experiment and for the first time in planetary exploration, Mars’ internal structure and seismicity are constrained.
• ▪  More than 1,300 seismic events and seismic noise records enable the first comparative seismology studies together with Earth and lunar seismic data.
• ▪  Inversion of seismic travel times and waveforms provided the first interior model of another terrestrial planet, down to the core.
• ▪  Several impacts were also seismically recorded with their craters imaged from orbit, providing the first data on impact dynamic on Mars.

Planets are expected to conclude their growth through a series of giant impacts: energetic, global events that significantly alter planetary composition and evolution. Computer models and theory have elucidated the diverse outcomes of giant impacts in detail, improving our ability to interpret collision conditions from observations of their remnants. However, many open questions remain, as even the formation of the Moon—a widely suspected giant-impact product for which we have the most information—is still debated. We review giant-impact theory, the diverse nature of giant-impact outcomes, and the governing physical processes. We discuss the importance of computer simulations, informed by experiments, for accurately modeling the impact process. Finally, we outline how the application of probability theory and computational advancements can assist in inferring collision histories from observations, and we identify promising opportunities for advancing giant-impact theory in the future.

• ▪  Giant impacts exhibit diverse possible outcomes leading to changes in planetary mass, composition, and thermal history depending on the conditions.
• ▪  Improvements to computer simulation methodologies and new laboratory experiments provide critical insights into the detailed outcomes of giant impacts.
• ▪  When colliding planets are similar in size, they can merge or escape one another with roughly equal probability, but with different effects on their resulting masses, densities, and orbits.
• ▪  Different sequences of giant impacts can produce similar planets, encouraging the use of probability theory to evaluate distinct formation hypothesis.