Sea-level fluctuations and deep-sea sedimentation rates

Sediment accumulation rate curves from 95 drilled cores from the Pacific basin and sea-level curves derived from continental margin seismic stratigraphy show that high biogenous sediment accumulation rates correspond to low eustatic sea levels for at least the last 48 million years. This relationship fits a simple model of high sea levels producing lower land/sea ratios and hence slower chemical erosion of the continents, and vice versa.     

Growth rates of phosphate nodules from the continental margin off peru

Modern sea-floor phosphorite nodules sampled from off the coast of Peru are shown to grow at rates of millimeters per thousand years in spite of the fact that the measured accumulation rates of the underlying sediment are two to four orders of magnitude faster. Phosphate nodules grow downward into soft sediment, and the rates of phosphorus accumulation into nodules are approximately equal to the upward diffusive flux of dissolved phosphate inferred from pore water profiles. These results demonstrate that phosphorus in nodules originates from regeneration in sediments rather than as a result of direct precipitation from bottom waters.     

Isotopic dating of strain fringe increments: duration and rates of deformation in shear zones

The time scales over which deformation in the Earth's crust remains localized in shear zones are poorly known, as are the associated strain rates. We have determined the longevity and rates of deformation using rubidium-strontium (Rb-Sr) microsampling dating of increments of fibrous strain fringes from a Pyrenean shear zone. The fibers grew quasi-continuously through a protracted deformation history between 87 and 50 million years ago, over a period comparable to that of an orogeny. During a short interval between 66 and 62 million years, a rise in strain rate from 1.1 x 10(-15) to 7. 7 x 10(-15) seconds(-1) occurred. This acceleration correlates with an abrupt change in fiber-growth direction and a stress-field inversion from gravitational collapse to renewed horizontal crustal shortening.     

Cope's rule, hypercarnivory, and extinction in North American canids

Over the past 50 million years, successive clades of large carnivorous mammals diversified and then declined to extinction. In most instances, the cause of the decline remains a puzzle. Here we argue that energetic constraints and pervasive selection for larger size (Cope's rule) in carnivores lead to dietary specialization (hypercarnivory) and increased vulnerability to extinction. In two major clades of extinct North American canids, the evolution of large size was associated with a dietary shift to hypercarnivory and a decline in species durations. Thus, selection for attributes that promoted individual success resulted in progressive evolutionary failure of their clades.     

The Large Crater Origin of SNC Meteorites

A large body of evidence strongly suggests that the shergottite, nakhlite, and Chassigny (SNC) meteorites are from Mars. Various mechanisms for the ejection of large rocks at martian escape velocity (5 kilometers per second) have been investigated, but none has proved wholly satisfactory. This article examines a number of possible ejection and cosmic-ray exposure histories to determine which is most plausible. For each possible history, the Melosh spallation model is used to estimate the size of the crater required to produce ejecta fragments of the required size with velocities >/=5 kilometers per second and to produce a total mass of solid ejecta consistent with the observed mass flux of SNC meteorites. Estimates of crater production rates on Mars are then used to evaluate the probability that sufficiently large craters have formed during the available time. The results indicate that the SNC meteorites were probably ejected from a very large crater (> 100 kilometers in diameter) about 200 million years ago, and that cosmic-ray exposure of the recovered meteorites was initiated after collisional fragmentation of the original ejecta in space at much later times (0.5 to 10 million years ago).     

A tsunami deposit at the cretaceous-tertiary boundary in Texas

At sites near the Brazos River, Texas, an iridium anomaly and the paleontologic Cretaceous-Tertiary boundary directly overlie a sandstone bed in which coarse-grained sandstone with large clasts of mudstone and reworked carbonate nodules grades upward to wave ripple-laminated, very fine grained sandstone. This bed is the only sandstone bed in a sequence of uppermost Cretaceous to lowermost Paleocene mudstone that records about 1 million years of quiet water deposition in midshelf to outer shelf depths. Conditions for depositing such a sandstone layer at these depths are most consistent with the occurrence of a tsunami about 50 to 100 meters high. The most likely source for such a tsunami at the Cretaceous-Tertiary boundary is a bolidewater impact.     

Tellurium Content of Marine Manganese Oxides and Other Manganese Oxides

Tellurium in amounts ranging from 5 to 125 parts per million was present in all of 12 samples of manganese oxide nodules from the floor of the Pacific and Indian oceans. These samples represent the first recognized points of high tellurium concentration in a sedimentary cycle. The analyses may lend support to the theory that the minor-element content of sea-floor manganese nodules is derived from volcanic emanations.     

Application of carbon isotope stratigraphy to late miocene shallow marine sediments, new zealand

A distinct (0.5 per mil) carbon-13/carbon-12 isotopic shift in the light direction has been identified in a shallow marine sedimentary sequence of Late Miocene age at Blind River, New Zealand, and correlated with a similar shift in Late Miocene Deep Sea Drilling Project sequences throughout the Indo-Pacific. A dated piston core provides an age for the shift of 6.2 +/- 0.1 million years. Correlations based on the carbon isotopic change require a revision of the previously established magnetostratigraphy at Blind River. The carbon shift at Blind River occurs between 6.2 and 6.3 +/- 0.1 million years before present. A new chronology provides an age for the evolutionary first appearance datum of Globorotalia conomiozea at 6.1 +/- 0.1 million years, the beginning of a distinct latest Miocene cooling event associated with the Kapitean stage at 6.2 +/- 0.1 million years, and the beginning of a distinct shallowing of water depths at 6.1 +/- 0.1 million years. The Miocene-Pliocene boundary as recognized in New Zealand is now dated at 5.3 +/- 0.1 million years. Extension of carbon isotope stratigraphy to other shallow Late Miocene sequences should provide an important datum for international correlation of Late Miocene shallow and deep marine sequences.     

GM(1,1)模型在烟台市人口预测中的应用

分析了1949~2004年烟台市人口变动状况,应用GM(1,1)灰色模型拟合了该地区人口数量,并对未来4年的人口数量进行了预测。结果显示,1949~2004年烟台市人口整体呈上升趋势,1960年有1个人口低谷值417.95万人;分别利用1949~2004年和1979~2004年人口数据建立GM(1,1)灰色模型,两者的拟合精度均较高,但后者要优于前者;利用1979~2004年人口数据建立的灰色模型预测未来4年内烟台市人口分别为664.45万、668.01万6、71.59万和675.19万人,人口有逐年缓慢上升的趋势。     

U-Pb ages from the neoproterozoic Doushantuo Formation, China

U-Pb zircon dates from volcanic ash beds within the Doushantuo Formation (China) indicate that its deposition occurred between 635 and 551 million years ago. The base records termination of the global-scale Marinoan glaciation and is coeval with similar dated rocks from Namibia, indicating synchronous deglaciation. Carbon isotopic and sequence-stratigraphic data imply that the spectacular animal fossils of the Doushantuo Formation are for the most part younger than 580 million years old. The uppermost Doushantuo Formation contains a pronounced negative carbonate carbon isotopic excursion, which we interpret as a global event at circa 551 million years ago.     

Periodicity of extinctions in the geologic past: deterministic versus stochastic explanations

The temporal spacing and the magnitude of major extinctions over the past 250 and 570 million years, based on the use of different metrics of extinction probability, are analyzed by comparing deterministic and stochastic explanations. The best-fitting time series model is a stochastic autoregressive model that displays a pseudoperiodic behavior with a cycle length of 31 million years for the past 250 million years, regardless of the metric of extinction probability. The periodicity lengthens and weakens when the analysis is extended to the entire Phanerozoic. The history of the probability of extinction for the entire Phanerozoic, based on time series analysis, does not support the reported bipartite distribution of Van Valen. Rather, the probability of extinction has decreased uniformly over Phanerozoic time whereas the inertia or stability of the biotic system after the Late Permian crisis has increased.     

Earliest Pleistocene hominid cranial remains from Dmanisi, Republic of Georgia: taxonomy, geological setting, and age

Archaeological excavations at the site of Dmanisi in the Republic of Georgia have uncovered two partial early Pleistocene hominid crania. The new fossils consist of a relatively complete cranium and a second relatively complete calvaria from the same site and stratigraphic unit that yielded a hominid mandible in 1991. In contrast with the uncertain taxonomic affinity of the mandible, the new fossils are comparable in size and morphology with Homo ergaster from Koobi Fora, Kenya. Paleontological, archaeological, geochronological, and paleomagnetic data from Dmanisi all indicate an earliest Pleistocene age of about 1.7 million years ago, supporting correlation of the new specimens with the Koobi Fora fossils. The Dmanisi fossils, in contrast with Pleistocene hominids from Western Europe and Eastern Asia, show clear African affinity and may represent the species that first migrated out of Africa.     

Anorthosite belts, continental drift, and the anorthosite event

Most anorthosites lie in two principal belts when plotted on a predrift continental reconstruction. Anorthosite ages in the belts cluster around 1300 +/- 200 million years and range from 1100 to 1700 million years. This suggests that anorthosites are the product of a unique cataclysmic event or a thermal event that was normal only during the earth's early history.     

Rubidium-strontium, uranium, and thorium-lead dating of lunar material

Rubidiuom and stronztiulm concentrations and strontium isotopic compositions have been measutred on whole rock samples and density fractions of microgabbro. Density fractionis on two rocks define isochrons of 3400 and 4500 million years with large uincertainties owing to low enrichment of radiogenic strontium. Lead from fine surface material is highly radiogenic. An age of 4750 million years has been calculated from the ratio of (207)Pb/(206)Pb. The concentrations of uiranium, thorium, and lead isotopes are consistent with the evolution of lead in a 4700-million-year-old closed system characterized by the ratios of uranium to lead and of thoriunm to lead in this sutrface material.     

Chaotic evolution of the solar system

The evolution of the entire planetary system has been numerically integrated for a time span of nearly 100 million years. This calculation confirms that the evolution of the solar system as a whole is chaotic, with a time scale of exponential divergence of about 4 million years. Additional numerical experiments indicate that the Jovian planet subsystem is chaotic, although some small variations in the model can yield quasiperiodic motion. The motion of Pluto is independently and robustly chaotic.     

Natural variability of Greenland climate, vegetation, and ice volume during the past million years

The response of the Greenland ice sheet to global warming is a source of concern notably because of its potential contribution to changes in the sea level. We demonstrated the natural vulnerability of the ice sheet by using pollen records from marine sediment off southwest Greenland that indicate important changes of the vegetation in Greenland over the past million years. The vegetation that developed over southern Greenland during the last interglacial period is consistent with model experiments, suggesting a reduced volume of the Greenland ice sheet. Abundant spruce pollen indicates that boreal coniferous forest developed some 400,000 years ago during the "warm" interval of marine isotope stage 11, providing a time frame for the development and decline of boreal ecosystems over a nearly ice-free Greenland.     

Volcanic dust in deep-sea sediments: relationship of microfeatures to explosivity estimates

Particle size variations in a series of volcanic ash layers, deposited in high latitudes of the South Pacific during the past 2.5 million years, were earlier analyzed by using a model in which source cloud height and minimum volcanic paleoexplosivity are derived from downwind ash distribution. Examination of submicrometer morphological features of the volcanic glass shards reveals a clear relationship between what appear to be impact features on the glass surfaces and the independently derived paleoexplosivities, which suggests that this may be a simple means to characterize ash horizons and estimate relative volcanic explosivities.     

莱芜市人口的具有外生变量的时间序列预测模型

基于人口总量与经济增长有强相关关系,结合时间序列预测模型的良好适应性,建立了将经济增长作为外生变量的人口时间序列预测模型,以莱芜市1989-2011年人口总量和GDP总量数据为例,建立了莱芜市人口发展趋势的含外生变量的时间序列模型,并对模型的精确度进行检验,模型结果精确度较为理想。然后对2012-2016年莱芜市人口总量及其增长速度进行了预测,结果显示,"十二五"期间莱芜市总人口在未来几年将保持年均增长量为0.4万人,环比平均增长速度为0.3%,人口总规模将近130万。     

Runcaria, a middle devonian seed plant precursor

The emergence of the seed habit in the Middle Paleozoic was a decisive evolutionary breakthrough. Today, seed plants are the most successful plant lineage, with more than 250,000 living species. We have identified a middle Givetian (385 million years ago) seed precursor from Belgium predating the earliest seeds by about 20 million years. Runcaria is a small, radially symmetrical, integumented megasporangium surrounded by a cupule. The megasporangium bears an unopened distal extension protruding above the multilobed integument. This extension is assumed to be involved in anemophilous pollination. Runcaria sheds new light on the sequence of character acquisition leading to the seed.     

Spontaneous mutation rates at five coat-color loci in mice

Examination of 1.5 million mice yielded natural mutation rates estimnated from 5.2 million gene reproductions at five specific coat-color loci. The average rates were 11.1 x 10(-6) for forward mutations and 2.7 x 10(-6) for reverse mutations. Differences between the frequencies of mutations at the individual loci were evident.