A long-lived lunar core dynamo

Paleomagnetic measurements indicate that a core dynamo probably existed on the Moon 4.2 billion years ago. However, the subsequent history of the lunar core dynamo is unknown. Here we report paleomagnetic, petrologic, and (40)Ar/(39)Ar thermochronometry measurements on the 3.7-billion-year-old mare basalt sample 10020. This sample contains a high-coercivity magnetization acquired in a stable field of at least ~12 microteslas. These data extend the known lifetime of the lunar dynamo by 500 million years. Such a long-lived lunar dynamo probably required a power source other than thermochemical convection from secular cooling of the lunar interior. The inferred strong intensity of the lunar paleofield presents a challenge to current dynamo theory.     

Seismic detection of the lunar core

Despite recent insight regarding the history and current state of the Moon from satellite sensing and analyses of limited Apollo-era seismic data, deficiencies remain in our understanding of the deep lunar interior. We reanalyzed Apollo lunar seismograms using array-processing methods to search for the presence of reflected and converted seismic energy from the core. Our results suggest the presence of a solid inner and fluid outer core, overlain by a partially molten boundary layer. The relative sizes of the inner and outer core suggest that the core is ~60% liquid by volume. Based on phase diagrams of iron alloys and the presence of partial melt, the core probably contains less than 6 weight % of lighter alloying components, which is consistent with a volatile-depleted interior.     

Abundances of 30 elements in lunar rocks, soil, and core samples

Abundances of 30 elements in seven lunar rocks and soil were determined by instrumental and radiochemical activation analysis. Seven major and minor elements in chips from 27 rocks were determined by instrumental activation analysis. Abundances of ten bulk elements overlap for the breccia rocks and soil samples. All lunar rare earth elements distribution patterns resemble those found in terrestrial abyssal subalkaline basalt, but with Eu depleted by about 60 percent in all lunar samples compared to the adjacent rare earth elements. Precipitation of plagioclase and hypersthene achondritic-like minerals from a melt could account for Eu depletion and the observed distribution of rare earth elements. Abundances of Ti, Al, Ca, Na, and Mn determined by instrumental activation analysis in five core-tube soil samples indicate uniformity for Al and Mn and apparent differences (10 to 20 percent) for Ti, Ca, and Na at 7.8 and 10.5 centimeters as compared to 0to5.2 centimeter depths.     

Apollo 11 drive-tube core samples: an initial physical analysis of lunar surface sediment

Two drive-tube core samples were obtained at Tranquillity Base. Fines include much glass, are unweathered, medium gray, loose, nonstructured, very weakly coherent, and demonstrate both accumulation and mixing in a waterless vacuum environment. In contrast to chemical weathering characteristic on the earth, lunar alteration processes are primarily mechanical. We infer that environmental processes of the lunar surface may be expressed as follows: R (regolith) = f(cl, p, r, t, b, a, . . .), in which climate (cl) is constant and the time (t)-de-pendent processes of bombardment (b) and accumulation (a) assume significance unparalleled on the earth because of their effects on parent material (p) and relief (r).     

The remanent magnetization of lunar soils

The magnetic material in the lunar soils makes them potentially strong carriers of remanence and magnetically viscous. The soils therefore block remanence in the temperature range of the lunar diurnal cycle. This remanence is stable against alternating-field demagnetization. A mechanism whereby such hard natural remanent magnetization may be acquired by material buried in the regolith is proposed.     

Apollo 12 lunar samples: trace element analysis of a core and the uniformity of the regolith

Four core and soil samples from Apollo 12 are enriched in a number of trace elements of meteoritic origin to virtually the same degree as Apollo 11 soil. An average meteoritic influx rate of about 4 x 10(-9) gram per square centimeter per year thus seems to be valid for the entire moon. A sample from a light gray, coarse-grained layer in the core resembles lunar basalts in composition, but is enriched by factors of 10(4) to 10(5) in bismuth and cadmium.     

Earthquake waves and the geomagnetic dynamo

It is proposed that earthquake waves energize the geomagnetic dynamo. Fluid motions generated by earthquakes may have enough energy to be in equipartition with fields as large as 100 gauss. Seismic waves from meteoritic impacts with energies sufficient to reverse the field occur every 170,000 years.     

Bistatic-radar detection of lunar scattering centers with lunar orbiter I

Continuous-wave signals transmitted from Lunar Orbiter I have been received on Earth after they have been reflected from the surface of the moon. The frequency spectrum of the reflected signals is used to locate discrete, heterogeneous, scattering centers on the lunar surface. The scattering centers are probably distinguished from the surrounding terrain by a higher surface reflectivity. Continuous-wave bistatic radar could provide an important new method for the study and mapping of planetary surfaces.     

Polarity transition records and the geomagnetic dynamo

The Parker-Levy approach to reversals of the geomagnetic field predicts meridional transitional paths of the virtual geomagnetic pole (VGP) which pass either through the site of observation or through its antipode, depending upon the site location and the sense of the polarity transition. Comparison with the most detailed transitional VGP path records presently available gives some indication of the above behavior as predicted by the Parker-Levy model. Discrepancies may be due to complexities in the distribution of cyclonic convection cells in the core not considered in the formal mathematical treatment. The predicted variation in transitional field intensity experienced at any given site also is compatible with several reported transition records.     

The apollo 15 lunar samples: a preliminary description

Samples returned from the Apollo 15 site consist of mare basalts and breccias with a variety of premare igneous rocks. The mare basalts are from at least two different lava flows. The bulk chemical compositions and textures of these rocks confirm the previous conclusion that the lunar maria consist of a series of extrusive volcanic rocks that are rich in iron and poor in sodium. The breccias contain abundant clasts of anorthositic fragments along with clasts of basaltic rocks much richer in plagioclase than the mare basalts. These two rock types also occur as common components in soil samples from this site. The rocks and soils from both the front and mare region exhibit a variety of shock characteristics that can best be ascribed to ray material from the craters Aristillus or Autolycus.     

Thermally driven rossby-mode dynamo for solar magnetic-field reversals

There is increasing interest in the possible existence of large eddies or "Rossby waves" in Sun's convection zone and photosphere. It is shown that many flows of this type, driven by an equator-pole temperature diffrence, act as hydromagnetic dynamos to produce magnetic fields that periodically reverse. The periods and field amplitudes agree with solar phenomena within an order of magnitude.     

Support for the lunar cataclysm hypothesis from lunar meteorite impact melt ages

Lunar meteorites represent a more random sampling of lunar material than the Apollo or Luna collections and, as such, lunar meteorite impact melt ages are the most important data in nearly 30 years with which to reexamine the lunar cataclysm hypothesis. Within the lunar meteorite breccias MAC 88105, QUE 93069, DaG 262, and DaG 400, seven to nine different impact events are represented with 40Ar-39Ar ages between 2.76 and 3.92 billion years ago (Ga). The lack of impact melt older than 3.92 Ga supports the concept of a short, intense period of bombardment in the Earth-moon system at approximately 3.9 Ga. This was an anomalous spike of impact activity on the otherwise declining impact- frequency curve.     

The selective cause of an ancient adaptation

Phylogenetic analysis reveals that the use of nicotinamide adenine dinucleotide phosphate (NADP) by prokaryotic isocitrate dehydrogenase (IDH) arose around the time eukaryotic mitochondria first appeared, about 3.5 billion years ago. We replaced the wild-type gene that encodes the NADP-dependent IDH of Escherichia coli with an engineered gene that possesses the ancestral NAD-dependent phenotype. The engineered enzyme is disfavored during competition for acetate. The selection intensifies in genetic backgrounds where other sources of reduced NADP have been removed. A survey of sequenced prokaryotic genomes reveals that those genomes that encode isocitrate lyase, which is essential for growth on acetate, always have an NADP-dependent IDH. Those with only an NAD-dependent IDH never have isocitrate lyase. Hence, the NADP dependence of prokaryotic IDH is an ancient adaptation to anabolic demand for reduced NADP during growth on acetate.     

中国古代史官制度及文化

中华民族向来具有发达的历史意识,十分重视历史的记载与传承,而通过国家建立行政色彩浓厚的史官制度功不可没。文章首先对我国古代史官制度的历史沿革进行了诠释,着重分析了我国古代史官制度的特征,并进一步探讨了考论得失,惩恶劝善的史官精神。