Partitioning of oxygen during core formation on the Earth and Mars

Core formation on the Earth and Mars involved the physical separation of metal and silicate, most probably in deep magma oceans. Although core-formation models explain many aspects of mantle geochemistry, they have not accounted for the large differences observed between the compositions of the mantles of the Earth (approximately 8 wt% FeO) and Mars (approximately 18 wt% FeO) or the smaller mass fraction of the martian core. Here we explain these differences as a consequence of the solubility of oxygen in liquid iron-alloy increasing with increasing temperature. We assume that the Earth and Mars both accreted from oxidized chondritic material. In a terrestrial magma ocean, 1,200-2,000 km deep, high temperatures resulted in the extraction of FeO from the silicate magma ocean owing to high solubility of oxygen in the metal. Lower temperatures of a martian magma ocean resulted in little or no extraction of FeO from the mantle, which thus remains FeO-rich. The FeO extracted from the Earth's magma ocean may have contributed to chemical heterogeneities in the lowermost mantle, a FeO-rich D" layer and the light element budget of the core.     

Origin of the Moon in a giant impact near the end of the Earth's formation

The Moon is generally believed to have formed from debris ejected by a large off-centre collision with the early Earth. The impact orientation and size are constrained by the angular momentum contained in both the Earth's spin and the Moon's orbit, a quantity that has been nearly conserved over the past 4.5 billion years. Simulations of potential moon-forming impacts now achieve resolutions sufficient to study the production of bound debris. However, identifying impacts capable of yielding the Earth-Moon system has proved difficult. Previous works found that forming the Moon with an appropriate impact angular momentum required the impact to occur when the Earth was only about half formed, a more restrictive and problematic model than that originally envisaged. Here we report a class of impacts that yield an iron-poor Moon, as well as the current masses and angular momentum of the Earth-Moon system. This class of impacts involves a smaller-and thus more likely-object than previously considered viable, and suggests that the Moon formed near the very end of Earth's accumulation.     

Accretion of the Earth and segregation of its core

The Earth took 30-40 million years to accrete from smaller 'planetesimals'. Many of these planetesimals had metallic iron cores and during growth of the Earth this metal re-equilibrated with the Earth's silicate mantle, extracting siderophile ('iron-loving') elements into the Earth's iron-rich core. The current composition of the mantle indicates that much of the re-equilibration took place in a deep (> 400 km) molten silicate layer, or 'magma ocean', and that conditions became more oxidizing with time as the Earth grew. The high-pressure nature of the core-forming process led to the Earth's core being richer in low-atomic-number elements, notably silicon and possibly oxygen, than the cores of the smaller planetesimal building blocks.     

Evidence for an oxygen-depleted liquid outer core of the Earth

On the basis of geophysical observations, cosmochemical constraints, and high-pressure experimental data, the Earth's liquid outer core consists of mainly liquid iron alloyed with about ten per cent (by weight) of light elements. Although the concentrations of the light elements are small, they nevertheless affect the Earth's core: its rate of cooling, the growth of the inner core, the dynamics of core convection, and the evolution of the geodynamo. Several light elements-including sulphur, oxygen, silicon, carbon and hydrogen-have been suggested, but the precise identity of the light elements in the Earth's core is still unclear. Oxygen has been proposed as a major light element in the core on the basis of cosmochemical arguments and chemical reactions during accretion. Its presence in the core has direct implications for Earth accretion conditions of oxidation state, pressure and temperature. Here we report new shockwave data in the Fe-S-O system that are directly applicable to the outer core. The data include both density and sound velocity measurements, which we compare with the observed density and velocity profiles of the liquid outer core. The results show that we can rule out oxygen as a major light element in the liquid outer core because adding oxygen into liquid iron would not reproduce simultaneously the observed density and sound velocity profiles of the outer core. An oxygen-depleted core would imply a more reduced environment during early Earth accretion.     

新风用地能降温除湿试验

分析了夏热冬冷地区居住建筑室外的气象条件和室内的通风要求,在夏季用地能对新风进行了降温除湿试验,试验结果表明,新风经地能降温除湿后其温湿度基本满足该地区居住建筑室内通风的要求,且系统运行稳定,效果良好。     

液核地球CIP轴的极移和岁差章动

基于经典的液核地球自转动力学理论,通过引入章动参考系相对惯性空间的运动,建立了液核地球极移和章动的联合动力学方程,由此对CIP轴进行了理论定义,并给出了其极移、岁差和章动的动力学方程,在顾及到5阶岁差章动力矩的情况下,给出了岁差章动的解析表达式,通过推导发现,即使没有核幔边界的耗散耦合,奇数阶岁差章动力矩也使得黄经章动和交角章动出现了异向项,即黄经章动出现了cos项,交角章动出现了sin项,同时还证明了岁差表达式与地球模型无关,本的理论可为动力大地测量学和天地球动力学的研究提供理论参考和依据。     

Deformation characteristics and formation mechanism of the Yunmengshan metamorphic core complex

The Yunmengshan metamorphic core complex in the middle part of the Yanshan Fold and Thrust Belt records crust extension processes of the eastern North China Craton during its peak destruction.Development of the metamorphic core complex was controlled by the generally NNE-striking Dashuiyu Shear Zone.The shear zone dips SE and becomes shallower NE-wards,leading to exposures of a ductile shear zone in the southern and middle parts and brittle faults in the northern part.Exposure structures,microstructures,and quartz C-axis fabrics indicate that the ductile shear zone belongs to an extensional shear zone with a top-to-the-SE shear sense.Deformation temperatures of 300–520°C suggest a midcrustal origin for the ductile shear zone.A ductile deformation belt in the footwall of the shear zone is only as wide as 1–3 km,indicating no widespread mid-crustal ductile flow in the region during the deformation.Zircon U–Pb dating of dykes and plutons as well as hornblende and biotite40Ar/39Ar dating demonstrate that the metamorphic core complex originated at 135 Ma and experienced intense shearing of the Dashuiyu Shear Zone,development of the supradetachment basins,and synkinematic intrusion during 135–125 Ma.The metamorphic core complex was subjected to rapid exhumation during 125–114 Ma when the Dashuiyu Shear Zone suffered continuous activity and passive doming.The shear zone and its hanging wall were cut or replaced by a series of brittle faults when they wereuplifted to a brittle regime,showing that exhumation took place in continuous extensional activities.The metamorphic core complex turned into slow exhumation in an extensional regime in the following latest Early Cretaceous.The evolution history suggests that the Yunmengshan metamorphic core complex was developed by the rolling-hinge model,a common formation mechanism for intraplate metamorphic core complexes in the North China Craton,under the continuous NW–SE extension during the Early Cretaceous(135–100 Ma).     

液核地球各种轴系的表述

 之前的整体地球自转动力学理论的局限性之一,就是在数学上不能明确表述地球的各种几何轴和物理轴(Tisserand轴、自转轴、瞬时形状轴、角动量轴、CEP和CIP轴等).基于经典的液核地球自转动力学理论,建立了极移和‘章动'的联合动力学方程.由此给出了液核地球各种几何轴和物理轴的极移、岁差章动的动力学方程,明确了各种轴的定义及其之间的理论关系.     

深部地层取心层裂机理研究

在深部高地应力地层中取心,岩心层裂(饼化)是一种常见的工程现象。岩心层裂和岩体的物性、力学性质以及原地应力密切相关。为研究钻井取心过程中岩心层裂现象的机理,结合川西南部地区Ａ井和B井取心过程中的岩心层裂现象,考虑岩石矿物组分与岩石脆性指数的关系,基于应力集中的非均匀岩石拉伸破坏模型,给出了岩心层裂现象产生的判据,采用理论计算和数值模拟方法对饼化现象进行了验证。研究结果表明：脆性矿物含量越高,岩石脆性越强,越易生成裂缝;岩心套取是一个卸载水平方向最大主应力的过程,卸载速度越快,损伤处的附加拉应力越大,且对应被激活损伤的尺寸就越小,当附加拉应力大于岩石抗拉强度时,会出现岩心层裂现象,随着取心的继续此过程将重复地发生下去。     

地冷耦合除湿型空调系统的热力学分析

地冷空调使用天然可再生的土壤冷源，在夏季某些室外条件下可为房间供冷，但室外温湿度很高时．独立的地冷空调系统无法满足空调舒适度标准．本文中提出一种新型地冷耦合除湿型空调系统。在地冷系统前耦合吸附器对空气预除湿，并在不同的室外条件下，对独立地冷空调和地冷耦合除湿型空调系统进行了热力学分析和对比．结果表明相对于独立的地冷空调，地冷耦合吸附除湿型空调系统的性能和可靠性提高．     

5·12地震-大熊猫栖息地灾后生态修复重建探讨

本文介绍了大熊猫生境以及大熊猫自身特征,同时阐述了汶川地震对四川大熊猫栖息地影响.最后,为了有效保护大熊猫,从大熊猫面临的威胁入手,提出恢复破坏的栖息地、加强生态走廊建设、生态环境综合治理、加强基地建设、加强国际科技合作等措施建议.     

Enhanced atmospheric loss on protoplanets at the giant impact phase in the presence of oceans

The atmospheric compositions of Venus and Earth differ significantly, with the venusian atmosphere containing about 50 times as much 36Ar as the atmosphere on Earth. The different effects of the solar wind on planet-forming materials for Earth and Venus have been proposed to account for some of this difference in atmospheric composition, but the cause of the compositional difference has not yet been fully resolved. Here we propose that the absence or presence of an ocean at the surface of a protoplanet during the giant impact phase could have determined its subsequent atmospheric amount and composition. Using numerical simulations, we demonstrate that the presence of an ocean significantly enhances the loss of atmosphere during a giant impact owing to two effects: evaporation of the ocean, and lower shock impedance of the ocean compared to the ground. Protoplanets near Earth's orbit are expected to have had oceans, whereas those near Venus' orbit are not, and we therefore suggest that remnants of the noble-gas rich proto-atmosphere survived on Venus, but not on Earth. Our proposed mechanism explains differences in the atmospheric contents of argon, krypton and xenon on Venus and Earth, but most of the neon must have escaped from both planets' atmospheres later to yield the observed ratio of neon to argon.