Microtektites, microkrystites, and spinels from a late pliocene asteroid impact in the southern ocean

The properties of glassy spherules found in sedimentary deposits of a late Pliocene asteroid impact into the southeast Pacific are similar to those of both microtektites and microkrystites. These spherules probably formed from molten silicate droplets that condensed from an impact-generate vapor cloud. The spherules contain inclusions of magnesioferrite spinels similar to those in spherules found at the Cretaceous-Tertiary boundary, indicating that both sets of spherules are impact debris formed under similar physical and chemical conditions.     

Staphylococcal alpha-toxin: effects on artificial lipid spherules

Staphylococcal alpha-toxin induces the release of previously sequestered anions or glucose from artificial phospholipid spherules, an effect abolished by specific antitoxin. Alphatoxin resembles streptolysin S in releasing anions or glucose from spherules prepared without cholesterol, and can be distinguished from the membrane-active polyene amphotericin B, which preferentially disrupts spherules containing cholesterol. It may affect biological structures by a similiar interaction with membrane phospholipids.     

鸡(土从)菌生活史的研究

通过孢子分离,小白球分离都在人工合成培养基上萌发成菌丝,形成小白球,证实小白球是鸡(土从)菌生活循环中的一个发育阶段.鸡(土从)菌担孢子萌发的单核菌丝,经过锁状联合发育成双核菌丝,继而形成小白球,但难以在培养基上长出子实体,而在蚁巢上合轴交叉的菌丝交织成小白球,再发育成原基,在适宜的环境条件下鸡(土从)菌破土而出形成子实体.本研究从无性循环及有性循环两方面初步阐明了鸡(土从)菌的生活史.     

Surface Features of Metallic Spherules

Metallic spherules of variable character have been recovered from Antarctic snow. Three types were recognized from their surface features: type 1, smooth, polished spherules, apparently produced by surface melting of the particles upon entry into the earth's atmosphere; type 11, spherules with a corrugated surface caused by differential hardness of internal, intersecting lamellae, but modified by superimposed pits; and type III, spherules with random, circular depressions or pits apparently resulting from impact with submicroscopic particles. Spherules of types II and III were too small to have suffered abrasion by impacts in the earth's atmosphere, and it is postulated that their surfaces may have been produced by erosion in space. Preservation of these surface details would have been possible if entry into the atmosphere took place at low velocities and low-angle trajectories.     

Lonar lake, India: an impact crater in basalt

Discovery of shock-metamorphosed material establishes the impact origin of Lonar Crater. Coarse breccia with shatter coning and microbreccia with moderately shocked fragments containing maskelynite were found in drill holes through the crater floor. Trenches on the rim yield strongly shocked fragments in which plagioclase has melted and vesiculated, and bombs and spherules of homogeneous rock melt. As the only known terrestrial impact crater in basalt, Lonar Crater provides unique opportunities for comparison with lunar craters. In particular, microbreccias and glass spherules from Lonar Crater have close analogs among the Apollo specimens.     

Black magnetic spherule fallout in the eastern gulf of Mexico

Large numbers of black metallic spherules ranging in diameter from a few micrometers to over 800 micrometers are raining into the eastern Gulf of Mexico and adjacent areas of western Florida. The composition of the flux, its association with glass spherules and coky particles, and its magnitude point to industrial pollution, probably coal- and coke-burning facilities around the perimeter of the gulf, as the source. Since metallic particles represent only a small fraction of most fly ash, such an influx of large numbers of black magnetic spherules must be symptomatic of a much higher rate of sedimentation of fly ash. The internal microstructures and the general appearance of spherules derived from industrial processes are similar to those of particles derived from cosmic sources. Because of the high potential for contamination in micrometeorite studies, a complete compositional verification of each "cosmic" particle may be necessary.     

Silicate spherules from tunguska impact area: electron microprobe analysis

The major oxide composition of four silicate spherules from the area of forest devastated by the explosion of the Tunguska meteorite has been determined by electron microprobe analysis. In general, the spherules have compositions similar to that of igneous glass except for the low iron and the high calcium oxide content of the three spherules that have a low content of silicon dioxide. None of the spherules seem to have compositions similar to the silicate portiof any major meteorite group.     

Polystyrene spherules in coastal waters

Polystyrene spherules averaging 0.5 millimeter in diameter (range 0.1 to 2 millimeters) are abundant in the coastal waters of southern New England. Two types are present, a crystalline (clear) form and a white, opaque form with pigmentation resulting from a diene rubber. The spherules have bacteria on their surfaces and contain polychlorinated biphenyls, apparently absorbed from ambient seawater, in a concentration of 5 parts per million. White, opaque spherules are selectively consumed by 8 species of fish out of 14 species examined, and a chaetognath. Ingestion of the plastic may lead to intestinal blockage in smaller fish.     

Chesterton soil concretions: ilmenite and not iron-manganese cementing matrix

Dark reddish-brown spherules are common in soils of the Chesterton soil series of a high marine terrace in southern California. The spherules are concretionary in structure and are bound by ilmenite rather than by an iron-manganese complex. The spherules have been mislabeled both with respect to structure and mineralogy.     

The Opportunity Rover's Athena science investigation at Meridiani Planum, Mars

The Mars Exploration Rover Opportunity has investigated the landing site in Eagle crater and the nearby plains within Meridiani Planum. The soils consist of fine-grained basaltic sand and a surface lag of hematite-rich spherules, spherule fragments, and other granules. Wind ripples are common. Underlying the thin soil layer, and exposed within small impact craters and troughs, are flat-lying sedimentary rocks. These rocks are finely laminated, are rich in sulfur, and contain abundant sulfate salts. Small-scale cross-lamination in some locations provides evidence for deposition in flowing liquid water. We interpret the rocks to be a mixture of chemical and siliciclastic sediments formed by episodic inundation by shallow surface water, followed by evaporation, exposure, and desiccation. Hematite-rich spherules are embedded in the rock and eroding from them. We interpret these spherules to be concretions formed by postdepositional diagenesis, again involving liquid water.     

Morphology and related chemistry of small lunar particles from tranquillity base

Glass spherules show multiple high-velocity impact craters and are coated with small particles including glass, plagioclase, clinopyroxene, ilmenite, olivine, chromite, rock fragments, and frozen droplets of iron, nickel-iron, and troilite. These spherules passed through an impact cloud of hot fragmental material, condensing iron-rich vapor and high-velocity projectiles. Breccia contains concentric, accretionary lapilli units and appears to be a sintered deposit from a hot lunar base surge generated by impact.     

Lunar impact history from (40)Ar/(39)Ar dating of glass spherules

Lunar spherules are small glass beads that are formed mainly as a result of small impacts on the lunar surface; the ages of these impacts can be determined by the (40)Ar/(39)Ar isochron technique. Here, 155 spherules separated from 1 gram of Apollo 14 soil were analyzed using this technique. The data show that over the last approximately 3.5 billion years, the cratering rate decreased by a factor of 2 to 3 to a low about 500 to 600 million years ago, then increased by a factor of 3.7 +/- 1.2 in the last 400 million years. This latter period coincided with rapid biotic evolutionary radiation on Earth.     

Soils of Eagle crater and Meridiani Planum at the Opportunity Rover landing site

The soils at the Opportunity site are fine-grained basaltic sands mixed with dust and sulfate-rich outcrop debris. Hematite is concentrated in spherules eroded from the strata. Ongoing saltation exhumes the spherules and their fragments, concentrating them at the surface. Spherules emerge from soils coated, perhaps from subsurface cementation, by salts. Two types of vesicular clasts may represent basaltic sand sources. Eolian ripples, armored by well-sorted hematite-rich grains, pervade Meridiani Planum. The thickness of the soil on the plain is estimated to be about a meter. The flatness and thin cover suggest that the plain may represent the original sedimentary surface.     

Silicate spherules from deep-sea sediments: confirmation of extraterrestrial origin

Silicate spherules produced by atmospheric melting of meteoric bodies are probably the most common form of extraterrestrial material on the earth. It has never been possible to positively identify such particles although it has been known for more than a century that silicate spherules of suspected extraterrestrial origin are present in deep-sea sediments. One such spherule has been identified as definitely extraterrestrial since its abundances of nonvolatile trace elements closely match those of primitive solar system material.     

Geological and geochemical record of 3400-million-year-old terrestrial meteorite impacts

Beds of sand-sized spherules in the 3400-million-year-old Fig Tree Group, Barberton Greenstone belt, South Africa, formed by the fall of quenched liquid silicate droplets into a range of shallow-to deep-water depositional environments. The regional extent of the layers, their compositional complexity, and lack of included volcanic debris suggest that they are not products of volcanic activity. The layers are greatly enriched in iridium and other platinum group elements in roughly chondritic proportions. Geochemical modeling based on immobile element abundances suggests that the original average spherule composition can be approximated by a mixture of fractionated tholeiitic basalt, komatiite, and CI carbonaceous chondrite. The spherules are thought to be the products of large meteorite impacts on the Archean earth.     

Nickel-iron spherules from aouelioul glass

Nickel-iron spherules, ranging from less than 0.2 to 50 microns in diameter and containing 1.7 to 9.0 percent Ni by weight, occur in glass associated with the Aouelloul crater. They occur in discrete bands of siliceous glass enriched in dissolved iron. Their discovery is significant tangible evidence that both crater and glass originated from terrestrial impact.     

Microtektites and mass extinctions: evidence for a late devonian asteroid impact

Glass spherules, similar to microtektites, have been found near the Frasnian-Famennian boundary (F/F) (Upper Devonian) at Senzeilles, Belgium, contemporaneous with one of the largest marine mass extinctions of the Phanerozoic. These spherules exhibit a wide range of compositions and display teardrop, dumbbell, and compound morphologies analogous to microtektites. In addition, they lack crystallites, have few or no vesicles, and have a low content of volatile material. These characteristics are supportive of an impact origin. The Siljan Ring (Sweden) and Charlevoix structure (Quebec,Canada) are candidate craters of this age. The presence of microtektites near the F/F boundary supports the hypothesis that an impact caused the Upper Devonian worldwide benthic mass extinctions.     

Corneal calcification

Superficial calcification was produced in the normal rabbit cornea by mild irradiation with a carbon dioxide laser. The calcification was entirely extracellular and closely resemnbled that observed in human band keratopathy, which was characterized as hydroxyapatite by x-ray diffraction. The electron-mnicroscopic appearance of calcific spheriules and conglomerates in early cornteal calcification is presented. The calcific spherules arise at the basal plasma membrane surface of the epithelial cells in close relation to their basement membrane.     

The formation conditions of chondrules and chondrites

Chondrules, which are roughly millimeter-sized silicate-rich spherules, dominate the most primitive meteorites, the chondrites. They formed as molten droplets and, judging from their abundances in chondrites, are the products of one of the most energetic processes that operated in the early inner solar system. The conditions and mechanism of chondrule formation remain poorly understood. Here we show that the abundance of the volatile element sodium remained relatively constant during chondrule formation. Prevention of the evaporation of sodium requires that chondrules formed in regions with much higher solid densities than predicted by known nebular concentration mechanisms. These regions would probably have been self-gravitating. Our model explains many other chemical characteristics of chondrules and also implies that chondrule and planetesimal formation were linked.     

Spatial Distribution of Phoronopsis viridis Hilton

When hot saturated solutions of thermal copolymers containing the 18 common amino acids are allowed to cool, huge numbers of uniform, microscopic, relatively firm, and elastic spherules separate. The place of this phenomenon in a comprehensive theory of original thermal generation of primordial living units is considered.