State Of Interior Research Articles

Chemical Composition, Mineralogy, and Physical Properties of the Moon’s Mantle: A Review

The problem of the internal structure of the Moon plays a special role in understanding its geochemistry and geophysics. The principal sources of information about the chemical composition and physical state of the deep interior are seismic experiments of the Apollo expeditions, gravity data from the GRAIL mission, and geochemical and isotopic studies of lunar samples. Despite the high degree of similarity of terrestrial and lunar matter in the isotopic composition of several elements, the problem of the similarity and/or difference in the major-component composition of the silicate shells of the Earth and its satellite remains unresolved. This review paper summarizes and critically analyzes information on the composition and structure of the Moon, examines the main contradictions between geochemical and geophysical classes models for the mantle structure, both within each class and between the classes, related to the estimation of the abundance of Fe, Mg, Si, Al, and Ca oxides, and analyzes bulk silicate Moon (BSM) models. The paper describes the principles of the approach to modeling the internal structure of a planetary body, based on the joint inversion of an integrated set of selenophysical, seismic, and geochemical parameters combined with calculations of phase equilibria and physical properties. Two new classes of the chemical composition of the Moon enriched in silica (∼50% SiO2) and ferrous iron (11–13% FeO, Mg# 79–81) relative to the bulk composition of the silicate component of the Earth (BSE) are discussed: (i) models E with terrestrial concentrations of CaO and Al2O3 (Earth-like models) and (ii) models M with higher contents of refractory oxides (Moon-like models), which determine the features of the mineralogical and seismic structure of the lunar interior. A probabilistic distribution of geochemical (oxide concentrations) and geophysical (P-, S-wave velocities and density) parameters in the four-layer lunar mantle within the range of permissible selenotherms was obtained. Systematic differences are revealed between contents of major oxides in the silicate shells of the Earth and the Moon. Calculations were carried out for the mineral composition, P-, S-wave velocities, and density of the E/M models, and two classes of conceptual geochemical models: LPUM (Lunar Primitive Upper Mantle) and TWM (Taylor Whole Moon) with Earth’s silica content (∼45 wt % SiO2) and different FeO and Al2O3 contents. Arguments are presented in support of the SiO2- and FeO-enriched (olivine pyroxenite) lunar mantle, which has no genetic similarity with Earth’s pyrolitic mantle, as a geochemical consequence of the inversion of geophysical parameters and determined by cosmochemical conditions and the mechanism that formed the Moon. The dominant mineral of the lunar upper mantle is high-magnesium orthopyroxene with a low calcium content (rather than olivine), as confirmed by Apollo seismic data and supported by spacecraft analysis of spectral data from a number of impact basin rocks. In contrast, the P- and S-wave velocities of the TWM and LPUM geochemical models, in which olivine is the dominant mineral of the lunar mantle, do not match Apollo seismic data. The geochemical constraints in the scenarios for the formation of the Moon are considered. The simultaneous enrichment of the Moon in both SiO2 and FeO relative to the pyrolitic mantle of the Earth is incompatible with the formation of the Moon as a result of a giant impact from terrestrial matter or an impact body (bodies) of chondritic composition and is in conflict with modern scenarios of the formation of the Moon and with similarities in the isotopic compositions of lunar and terrestrial samples. The problem of how to fit these different geochemical factors into the Procrustean bed of cosmogonic models for the Earth–Moon system formation is discussed.

Solidus melting of pyrolite and bridgmanite: Implication for the thermochemical state of the Earth's interior

Melting properties of the deep mantle remain controversial due to experimental difficulties; e.g., reports of solidus temperatures of mantle-relevant compositions span over ∼700 K at 2000 km depth. This situation limits our understanding of the thermochemical state of the Earth's interior. Using the laser heated diamond anvil cell (LH-DAC), we performed new experimental determination of the solidus profile of ultra-dry pyrolite and the solidus of two compositions of (Mg,Fe)(Si,Al)O3 bridgmanite (Bg). Melting was detected (i) from -the correlation between laser power and sample temperature, -changes of sample texture and -the level of visible light absorption, for all samples, (ii) using X-ray diffraction, for the MgSiO3 composition and (iii) after scanning electron microscope observations, for selected Fe-bearing samples. Special care was given to using ultra-dry experimental chambers and to determination of sample temperature. In particular, we discuss the wavelength-dependent thermal emission of silicate samples, which lowers the solidus by 100 to 300 K, compared to the grey-body assumption.The solidus of MgSiO3-Bg is in good agreement with previous reports using ab initio calculations and shock wave experiments. We observe a net decrease in the solid-liquid Clapeyron slope at 60(3) GPa and 4400(200) K, which can be related to rapid pressure-induced coordination change of Si in the melt. (Mg0.955,Fe0.045)(Si0.993,Al0.007)O3 Bg melts 600–800 K lower than MgSiO3-Bg. Its solidus evolves smoothly with pressure, suggesting progressive Si coordination change in the melt. In the pressure range investigated (24–135 GPa) Clapeyron slopes suggest rapid decrease of the volume of fusion, from 14 to 2% for MgSiO3 and from 9 to 3% for (Fe,Al)-bearing Bg, assuming congruent melting. By comparing the solidii of various silicates, it appears that the higher the number of cations, the less pronounced is the curvature of the solidus. This observation suggests that the relatively ordered structure of simple liquid compositions with a limited number of distinct network-modifying cations frustrates the coexistence of tetrahedrally and octahedrally coordinated Si polyhedral.The solidus of pyrolite presents a smooth evolution from 2200(100) K to 3950(200) K in the same pressure interval. This is very similar to our previous work on chondritic-type mantle. The new solidus is 200–300 K lower than that of KLB-1 peridotite, which can be related to more incompatible elements in pyrolite. It remains problematic that our solidus plots several 100 K higher than other recent measurements performed on pyrolite; we discuss the possibility of a higher water content in previous samples, compared to our experiments. Assuming a dry lowermost mantle, our results imply a core-mantle boundary temperature lower than 3950(200) K. Modeling the melting diagram at the core-mantle boundary suggests a pseudo-eutectic melt significantly depleted in SiO2, compared to the composition of the mean mantle.

A Reduced Order Approach for Probabilistic Inversions of 3D Magnetotelluric Data II: Joint Inversion of MT and Surface‐Wave Data

AbstractJoint probabilistic inversions of magnetotelluric (MT) and seismic data have great potential for imaging the thermochemical structure of the lithosphere as well as mapping fluid/melt pathways and regions of mantle metasomatism. In this contribution, we present a novel probabilistic (Bayesian) joint inversion scheme for 3D MT and surface‐wave dispersion data particularly designed for large‐scale lithospheric studies. The approach makes use of a recently developed strategy for fast solutions of the 3D MT forward problem (Manassero et al., 2020,https://doi.org/10.1093/gji/ggaa415) and combines it with adaptive Markov chain Monte Carlo (MCMC) algorithms and parallel‐in‐parallel strategies to achieve extremely efficient simulations. To demonstrate the feasibility, benefits and performance of our joint inversion method for imaging the temperature and conductivity structures of the lithosphere, we apply it to two numerical examples of increasing complexity. The inversion approach presented here is timely and will be useful in the joint analysis of MT and surface wave data that are being collected in many parts of the world. This approach also opens up new avenues for the study of trans‐lithospheric and trans‐crustal magmatic systems, the detection of metasomatized mantle, and the incorporation of MT into multi‐observable inversions for the physical state of the Earth's interior.

Paleomagnetism of 3.5-4.0 Ga zircons from the Barberton Greenstone Belt, South Africa

The existence of a core dynamo during the first billion years of Earth history is closely related to the thermal state of the Earth's interior and composition of the early atmosphere. The scarcity of well-preserved rock units older than 3.5 billion years (Ga) has motivated the paleomagnetic analysis of detrital zircons. Studies of zircons from Jack Hills, Australia, however, have found the pervasive occurrence of secondary ferromagnetic minerals, casting doubt on the ability of these zircons to record a >3.5 Ga geomagnetic field. Here we report paleomagnetic analyses on a set of 19 zircons with crystallization age 3.5-4.0 Ga from the Barberton Greenstone Belt (BGB) of South Africa, which have undergone lower grade metamorphism compared to all other known >3.5 Ga detrital zircon localities. We find that BGB zircons have magnetic moments nearly one order of magnitude weaker than Jack Hills zircons, precluding the retention of primary paleomagnetic information. This result corroborates findings from the Jack Hills and other Archean zircon populations that primary ferromagnetic inclusions are readily eliminated from zircons during sedimentary transport and metamorphism, likely facilitated by radiation damage-induced permeability. Paleomagnetic determination of geodynamo activity prior to 3.5 Ga may require investigation of other detrital grains with lower radiation damage potential or whole-rock samples that have escaped high degree metamorphism.

FEATURES OF CALCULATION OF THE TEMPERATURE STATE OF THE BUS SALON

The safety of passenger transportation is not only to prevent accidents but also to ensure the conditions of health and efficiency of passengers and driver and the comfort of moving, which is guaranteed by the microclimate in the bus and the driver's workplace. One of the principal indicators of the microclimate is the air temperature in the cabin. The purpose of the work is to develop and substantiate the method of calculating the temperature of the bus interior.Unorganized air exchange due to body leaks (infiltration) influence on the thermal regime of the bus interior. Air exchange due to body leaks depends linearly on the speed of the bus. Heat loss through the structural elements of the body linearly depends on the outside air temperature.The calculation of the thermal state of the bus interior, in principle, is reduced to the estimation of the calorific value of the liquid heater, taking into account all heat losses in the cabin. The method of calculation developed on two indicators: experimentally defined coefficient of heat transfer of a body of the city bus and its inverse size, the calculated value of thermal resistance of unit of the area of salon of the bus. The thermal regime of the interior of a city bus in the conditions of winter operation is significantly influenced by heat exchange through the openings of open doors at short-term service stops. As for long-distance coaches, open the passenger door is much less. Therefore at the operation of buses of the specified class, it is necessary to give in salon-fresh air which needs to be heated.Since there are statistics on heat transfer of the body of city buses, the temperature of their cabins proposes to be calculated by the heat transfer coefficient of the bus body.In this method, the calculation depends on the heat transfer coefficient of the body. The supply and heating of air for ventilation are not taken into account, as the passenger door carries out air exchange in the cabin during bus stops.As calculations have shown, heat losses primarily depend on the temperature difference between the outside air and in the cabin. However, statistics on heat transfer of intercity (tourist) bus bodies are not currently available in the available publications. The temperature condition of intercity buses must correspond to the following calculations, inverse to the heat transfer coefficient of the body - thermal resistance per unit area of the bus.The method of calculating the temperature of the bus interior is substantiated. For city buses should be based on the calculation of heat transfer coefficients body. The temperature condition of intercity buses must be calculated from the thermal resistance per unit area of the bus interior. We proved that heat losses in the cabin of intercity buses, compared to city buses, are much lower due to the absence of heat losses at service stops at the exit and entry of passengers, which account for more than half of all heat losses. To reduce heat loss, the use of double-glazed windows instead of single panes has a particularly significant effect.

Mantle plumes are oxidised

From oxic atmosphere to metallic core, the Earth's components are broadly stratified with respect to oxygen fugacity. A simple picture of reducing oxygen fugacity with depth may be disrupted by the accumulation of oxidised crustal material in the deep lower mantle, entrained there as a result of subduction. While hotspot volcanoes are fed by regions of the mantle likely to have incorporated such recycled material, the oxygen fugacity of erupted hotspot basalts had long been considered comparable to or slightly more oxidised than that of mid-ocean ridge basalt (MORB) and more reduced than subduction zone basalts. Here we report measurements of the redox state of glassy crystal-hosted melt inclusions from tephra and quenched lava samples from the Canary and Cape Verde Islands, that we can independently show were entrapped prior to extensive sulphur degassing. We find high ferric iron to total iron ratios (Fe3+/∑Fe) of up to 0.27–0.30, indicating that mantle plume primary melts are significantly more oxidised than those associated with mid-ocean ridges and even subduction zone. These results, together with previous investigations from the Erebus, Hawaiian and Icelandic hotspots, confirm that mantle upwelling provides a return flow from the deep Earth for components of oxidised subducted lithosphere and suggest that highly oxidised material accumulates or is generated in the lower mantle. The oxidation state of the Earth's interior must therefore be highly heterogeneous and potentially locally inversely stratified.

On the clinical significance of concepts in psychosomatic medicine. A plea for conceptual research

Micelle plays an important role both in scientific research and practical applications. However, the problem about the state of micelle interior has not been completely solved. Based on the molecular dynamics (MD) simulation, absolute configurational entropies of hydrophobic chain are calculated to give a correct description of micelle hydrophobic interior. N-dodecyl betaine (NDB) and n-tridecane (C13), which have the same number of methylene group, are investigated in the present study. Results including total entropy, translational entropy, rotational entropy as well as vibrational entropy are calculated and compared between alkyl chains of NDB micelle and liquid C13. Local entropies along NDB alkyl chain and those between micelle and C13 are also considered. Through these comparisons, we explicitly propose that innermost groups of hydrophobic chains, where carbon number is no more than two, are identical to pure alkane whilst the outer core in the micelle shows the liquidlike state at the molecular level. The detailed information of micelle interior is the foundation for understanding micelle applications, such as solubilization, drug delivery and catalysis.

A molecular dynamics study combining with entropy calculation on the packing state of hydrophobic chains in micelle interior

Micelle plays an important role both in scientific research and practical applications. However, the problem about the state of micelle interior has not been completely solved. Based on the molecular dynamics (MD) simulation, absolute configurational entropies of hydrophobic chain are calculated to give a correct description of micelle hydrophobic interior. N-dodecyl betaine (NDB) and n-tridecane (C13), which have the same number of methylene group, are investigated in the present study. Results including total entropy, translational entropy, rotational entropy as well as vibrational entropy are calculated and compared between alkyl chains of NDB micelle and liquid C13. Local entropies along NDB alkyl chain and those between micelle and C13 are also considered. Through these comparisons, we explicitly propose that innermost groups of hydrophobic chains, where carbon number is no more than two, are identical to pure alkane whilst the outer core in the micelle shows the liquidlike state at the molecular level. The detailed information of micelle interior is the foundation for understanding micelle applications, such as solubilization, drug delivery and catalysis.

Ultra-High Pressure Dynamic Compression of Geological Materials

Dynamic compression experiments on geological materials are important for understanding the composition and physical state of the deep interior of the Earth and other planets. These experiments also provide insights into impact processes relevant to planetary formation and evolution. Recently, new techniques for dynamic compression using high-powered lasers and pulsed-power systems have been developed. These methods allow for compression on timescales ranging from nanoseconds to microseconds and can often achieve substantially higher pressures than earlier gas-gun-based loading techniques. The capability to produce shockless (ramp) compression provides access to new regimes of pressure-temperature space while new diagnostics allow for a more detailed understanding of the structure and physical properties of materials under dynamic loading. This review summarizes these recent advances, focusing on results for geological materials at ultra-high pressures above 200 GPa.

1D geothermal inversion of the lunar deep interior temperature and heat production in the equatorial area

We present a study on lunar interior temperature and heat production by 1D geothermal inversion. With the layered structure and thermal state of the lunar interior reported by lunar seismic and magnetic sounding research, a forward modeling of deep temperature is given based on the theory of thermal conduction. Then, the particle swarm optimization (PSO) method is applied to implement the inversion of lunar interior heat production. A six-layer model is solved using a global heat flux of 12 mW/m2 and a near-surface temperature of 250 K. The inversion results show that the crust has an average heat production of approximately 210 nW/m3, the mantle has a depleted heat production varying from 3.7 to 8.1 nW/m3, and the heat production in the lunar core varies from 30 to 36 nW/m3. The distribution of heat production indicates that the present radioisotopes are mainly concentrated in the lunar crust. Different from previous estimates, the heat release in the lunar core may be considerable, similar to the average heat production in the Moon, implying that the residual heat from lunar accretion or radioactive decay is probably substantial; in contrast, perhaps the core was involved to a limit in the material exchange with the mantle. In addition, the obtained heat flux at the core-mantle boundary meets the value required for the core adiabatic process, indicating that the core convection may have stopped.

Classification Modelling for the Impact of Historical Site on Residential Property Rental Value in Osogbo, Nigeria

Previous studies have revealed that historical sites have impact on property value. However, none of the previous studies have forecasted the impact of historical site on residential property value using a classification model. Data for the study were gathered from the record of recent letting in the study area. For the purpose of precision, this study adopted artificial neural network, logistic regression and support vector machine as model of classifying the rental value of residential property in Osogbo, Nigeria. The study considered relevant variables which include distance to cultural site, age of building, state of exterior and state of interior as input variables. Findings from the study revealed that the three adopted forecasting models have over 80% percent of the forecasted properties correctly classified which make the property forecasting reliable.

Tidal Records as Liquid Climate Archives for Large-Scale Interior Mediterranean Variability

Characterization of interior ocean variability is necessary for understanding climate. Water mass evolution shapes ocean-atmosphere interactions and contributes to determine timescales for global and regional climate variability. However, a robust assessment of past state and variability of the ocean interior is prevented by sparseness/shortness of historical subsurface observations and uncertainties affecting proxy-based reconstructions. Here, we propose a novel approach to infer past large-scale interior ocean variability with unprecedented accuracy and temporal resolution. It exploits links between stratification determined by “large-scale” water mass distributions and local dynamics. We characterize interannual interior ocean variability in the Mediterranean Sea in the early 20th century contained in tidal measurements in the Strait of Messina, and demonstrate the general applicability of our method, paving the way to a new approach to analyze historical oceanographic records: Regions where different water masses are known to collide can thus act as magnifying glasses for basin-scale interior ocean variability, hence providing “liquid archives” for climatology.

Density‐Pressure Profiles of Fe‐Bearing MgSiO3 Liquid: Effects of Valence and Spin States, and Implications for the Chemical Evolution of the Lower Mantle

AbstractDensity is a key property controlling the chemical state of Earth's interior. Our knowledge about the density of relevant melt compositions is currently poor at deep‐mantle conditions. Here we report results from first‐principles molecular‐dynamics simulations of Fe‐bearing MgSiO3 liquids considering different valence and spin states of iron over the whole mantle pressure conditions. Our simulations predict the high‐spin to low‐spin transition in both ferrous and ferric iron in the silicate liquid to occur gradually at pressures around 100 GPa. The calculated iron‐induced changes in the melt density (about 8% increase for 25% iron content) are primarily due to the difference in atomic mass between Mg and Fe, with smaller contributions (<2%) from the valence and spin states. A comparison of the predicted density of mixtures of (Mg,Fe)(Si,Fe)O3 and (Mg,Fe)O liquids with the mantle density indicates that the density contrast between the melt and residual‐solid depends strongly on pressure (depth): in the shallow lower mantle (depths < 1,000 km), the melt is lighter than the solids, whereas in the deep lower mantle (e.g., the D″ layer), the melt density exceeds the mantle density when iron content is relatively high and/or melt is enriched with Fe‐rich ferropericlase.

Quantum hair of black holes out of equilibrium

Classically, the black hole (BH) horizon is completely opaque, hiding any clues about the state and very existence of its interior. Quantum mechanically and in equilibrium, the situation is not much different: Hawking radiation will now be emitted, but it comes out at an extremely slow rate, is thermal to a high degree of accuracy and thus carries a minimal amount of information about the quantum state within the BH. Here, it is shown that the situation is significantly different when a quantum BH is out of equilibrium. We argue that the BH can then emit "supersized" Hawking radiation with a much larger amplitude than that emitted in equilibrium. The result is a new type of quantum hair that can reveal the state and composition of the BH interior to an external observer. Moreover, the frequency and amplitude of the new hair can be explained by the observer without invoking any new physical principles. The new hair decays at a parametrically slow rate in comparison to the Schwarzschild time scale and can be detected through the emission of gravitational waves (and possibly other types of waves); for example, during and after a BH-merger event. The current discussion is motivated by a previous analysis, in the context of a recently proposed polymer model for the BH interior, that implies emissions just like those described here. We expect, however, that the new hair is a model-independent property of quantum BHs.

The state of Hawking radiation is non-classical

We show that the state of the Hawking radiation emitted from a large Schwarzschild black hole (BH) deviates significantly from a classical state, in spite of its apparent thermal nature. For this state, the occupation numbers of single modes of massless asymptotic fields, such as photons, gravitons and possibly neutrinos, are small and, as a result, their relative fluctuations are large. The occupation numbers of massive fields are much smaller and suppressed beyond even the expected Boltzmann suppression. It follows that this type of thermal state cannot be viewed as classical or even semiclassical. We substantiate this claim by showing that, in a state with low occupation numbers, physical observables have large quantum fluctuations and, as such, cannot be faithfully described by a mean-field or by a WKB-like semiclassical state. Since the evolution of the BH is unitary, our results imply that the state of the BH interior must also be non-classical when described in terms of the asymptotic fields. We show that such a non-classical interior cannot be described in terms of a semiclassical geometry, even though the average curvature is sub-Planckian.

Depth-dependent δ13C trends in platform and slope settings of the Campbellrand-Malmani carbonate platform and possible implications for Early Earth oxygenation

The evolution of oxygenic photosynthesis is widely seen as the major biological factor for the profound shift from reducing to slightly oxidizing conditions in Earth’s atmosphere during the Archean-Proterozoic transition period. The delay from the first biogenic production of oxygen and the permanent oxidation of Earth’s atmosphere during the early Paleoproteorozoic Great Oxidation Event (GOE) indicates that significant environmental modifications were necessary for an effective accumulation of metabolically produced oxygen. Here we report a distinct temporal shift to heavier carbon isotope signatures in lagoonal and intertidal carbonates (δ13Ccarb from −1.6 to +0.4‰, relative to VPDB) and organic matter (δ13Corg from about −40 to −25‰, relative to VPDB) from the 2.58–2.50Gy old shallow-marine Campbellrand-Malmani carbonate platform (South Africa). This indicates an enhanced primary production and lateral transport of organic material offshore to greater depths as well as a change from an anaerobic to an aerobic ecosystem. Trace element data indicate limited influx of reducing species from deep open ocean water into the platform and an increased supply of nutrients from the continent, both supporting primary production and an increasing oxidation state of the platform interior. These restricted conditions allowed that the dissolved inorganic carbon (DIC) pool in the platform interior developed differently than the open ocean. This is supported by coeval carbonates from the marginal slope setting, which had a higher interaction with open ocean water and do not record a comparable shift in δ13Ccarb throughout the sequence. We propose that the emergence of stable shallow-water carbonate platforms in the Neoarchean provided ideal conditions for the evolution of early aerobic ecosystems, which finally led to the full oxidation of Earth’s atmosphere during the GOE.

Constraints on dissipation in the deep interiors of Ganymede and Europa from tidal phase-lags

Jupiter’s satellites are subject to strong tidal forces which result in variations of the gravitational potential and deformations of the satellites’ surfaces on the diurnal tidal cycle. Such variations are described by the Love numbers $$k_2$$ and $$h_2$$ for the tide-induced potential variation due to internal mass redistribution and the radial surface displacement, respectively. The phase-lags $$ \phi _{k_2}$$ and $$ \phi _{h_2}$$ of these complex numbers contain information about the rheological and dissipative states of the satellites. Starting from interior structure models and assuming a Maxwell rheology to compute the tidal deformation, we calculate the phase-lags in application to Ganymede and Europa. For both satellites we assume a decoupling of the outer ice-shell from the deep interior by a liquid subsurface water ocean. We show that, in this case, the phase-lag difference $$\varDelta \phi = \phi _{k_2}- \phi _{h_2}$$ can provide information on the rheological and thermal state of the deep interiors if the viscosities of the deeper layers are small. In case of Ganymede, phase-lag differences can reach values of a few degrees for high-pressure ice viscosities $${<}10^{14}$$ Pa s and would indicate a highly dissipative state of the deep interior. In this case $$\varDelta \phi $$ is dominated by dissipation in the high-pressure ice layer rather than dissipation within the ice-I shell. These phase lags would be detectable from spacecraft in orbit around the satellite. For Europa $$\varDelta \phi $$ could reach values exceeding $$20^\circ $$ and phase-lag measurements could help distinguish between (1) a hot dissipative silicate mantle which would in thermal equilibrium correspond to a very thin outer ice-I shell and (2) a cold deep interior implying that dissipation would mainly occur in a thick (several tens of km) outer ice-I shell. These measurements are highly relevant for ESA’s Jupiter Icy Moons Explorer (JUICE) and NASA’s Europa Multiple Flyby Mission, both targeted for the Jupiter system.

Quantum state of the black hole interior

If a black hole (BH) is initially in an approximately pure state and it evaporates by a unitary process, then the emitted radiation will be in a highly quantum state. As the purifier of this radiation, the state of the BH interior must also be in some highly quantum state. So that, within the interior region, the mean-field approximation cannot be valid and the state of the BH cannot be described by some semiclassical metric. On this basis, we model the state of the BH interior as a collection of a large number of excitations that are packed into closely spaced but single-occupancy energy levels; a sort-of "Fermi sea" of all light-enough particles. This highly quantum state is surrounded by a semiclassical region that lies close to the horizon and has a non-vanishing energy density. It is shown that such a state looks like a BH from the outside and decays via gravitational pair production in the near-horizon region at a rate that agrees with the Hawking rate. We also consider the fate of a classical object that has passed through to the BH interior and show that, once it has crossed over the near-horizon threshold, the object meets its demise extremely fast. This result cannot be attributed to a "firewall", as the trauma to the in-falling object only begins after it has passed through the near-horizon region and enters a region where semiclassical spacetime ends but the energy density is still parametrically smaller than Planckian.

Magnetic meteorites and the early solar system

Today, the Earth generates a magnetic field through convection of the electrically conducting molten iron in its outer core. Core convection is governed by the thermal and chemical processes that operate deep within our planet; thus measurements of the intensity and direction of the magnetic field can provide insights into the thermochemical state of the Earth's interior. Crustal rocks can also record and preserve a memory of the field they experienced as they were forming. Paleomagnetic measurements can therefore provide records of ancient magnetic activity and, by extension, the internal conditions of our planet in the past (Tarduno et al. 2014). A combination of paleomagnetic and present-day magnetic measurements therefore allow us to study the long-term and large-scale evolution of our planet over billions of years; this method could also potentially allow us to predict how it may behave in the future.

地球物質情報に基づく地球熱史解明：到達点の概観と今後の展開

Approaches to elucidate thermal history of the earth based on information of earth materials are reviewed. Limitations of these approaches are examined, and ways for the improvement and additional approaches to better constrain the thermal history of the earth are proposed. A short note of the current thermal status of the earth is followed by examination of earth's thermal history based on geophysical modeling of mantle convection, combination of which with material information is essential to deepen our understanding. There are several proxies of earth materials for secular changes of the thermal state of the earth's interior. Those often used so far are: (1) chemical composition of magmas, from which ‘potential temperatures’ of the ambient mantle are estimated, (2) pressure and temperature conditions of crustal materials (metamorphic rocks), from which ‘metamorphic geothermal gradients’ are estimated, (3) thickness of the crust and lithosphere, from which thermal gradients of the crust and lithosphere are estimated along with the temperature estimation of the bottoms, and (4) pressure and temperature of mantle materials, from which ‘mantle geothermal gradients’ of the lithosphere are estimated. Each method has problems to be resolved for quantitative estimation of the secular variation of the earth's thermal state. The following approaches are proposed: (1) coupling thickness of oceanic crust and depletion zone of residual mantle and major element composition of volcanic rocks, (2) high-resolution analysis of thermal history of crust and mantle materials to better constrain steady-state geotherms, and (3) simultaneous estimation of ambient pressure and temperature as well as mantle potential temperature from analysis of magma intrusions in the crust. Finally, the importance of extraterrestrial materials and earth-like exoplanets to reveal thermal history of the early earth, for which direct information is not available, is remarked.