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1.
Enrichments in boron-10/boron-11 in a calcium-aluminum-rich inclusion from the Allende carbonaceous chondrite are correlated with beryllium/boron in a manner indicative of the in situ decay of short-lived beryllium-10. Because this radionuclide is produced only by nuclear spallation reactions, its existence in early solar system materials attests to intense irradiation processes in the solar nebula. The particle fluence inferred from the initial beryllium-10/beryllium-9 is sufficient to produce other short-lived nuclides, calcium-41 and manganese-53, found in meteorites, but the high canonical abundance of aluminum-26 may still require seeding of the solar system by radioactive stellar debris. 相似文献
2.
Activities of aluminum-26 and beryllium-10 in marine sediment were measured at 0.01 +/- 0.13 and 4.4 +/- 0.9 disintegrations per minute, per kilogram dry weight, respectively. Only an upper limit of 0.03 could be determined for the ratio of aluminum-26 to beryllium-10 in the sediment. The ratio is probably explained by production by cosmic rays in the atmosphere. 相似文献
3.
Lower Pliocene hominid remains from Sterkfontein 总被引：2，自引：0，他引：2
Cosmogenic aluminum-26 and beryllium-10 burial dates of low-lying fossiliferous breccia in the caves at Sterkfontein, South Africa, show that associated hominid fossils accumulated in the Lower Pliocene. These dates indicate that the skeleton StW 573 and newly discovered specimens from Jacovec Cavern have much the same age: approximately 4 million years. These specimens are thus of an age similar to Australopithecus anamensis from East Africa. 相似文献
4.
Despite marine evidence for at least 50 Pliocene-Pleistocene ice sheet advances, only the most recent one has been accurately reconstructed from terrestrial evidence, because there are few techniques for dating older glacial deposits. Here we show that the cosmic ray-produced nuclides beryllium-10 and aluminum-26 can be used to date tills that overlie paleosols. 相似文献
5.
Activities of beryllium-10 and aluminum-26 dissolved in 200-year-old Greenland ice were found to be 18.4 (+ 8.4, - 4.8) x 10(-6) and 3.2 +/- 0.9 x 10(-7) disintegration per minute per liter, respectively. From these values and the precipitation rate (30 milliliters of water per square centimeter per year), the production rates of these isotopes are calculated to be 3.6 (+ 1.6, - 0.9) x 10(-2) and 1.7 +/- 0.5 x 10(-4) atom per second * square centimeter. These rates agree with the rates calculated for the production of these isotopes by cosmic rays in the atmosphere. Probably all the Al(26) in the ice is accounted for by such atmospheric production; however, an upper limit for the influx of cosmic dust bearing aluminum-26 is calculated at 3.2 x 10(5) tons per year for Earth. Only upper limits could be found for Al(26) and Be(10) in the undissolved particulate matter in the ice; their addition to the activities in the dissolved material leaves our conclusions unchanged. 相似文献
6.
Rancitelli LA Perkins RW Cooper JA Kaye JH Wogman NA 《Science (New York, N.Y.)》1969,166(3910):1269-1272
The concentrations of beryllium-7, sodium-22, aluminum-26, potassium-40, scandium-46, vanadium-48, chromium-51, manganese-54, cobalt-57, cobalt-60, and thorium-232 (thallium-208) have been measured in the Allende meteorite by nondestructive gamma-ray spectrometry. The high cobalt-60 content of the meteorite is indicative of a preatmospheric body with a minimum effective radius of 50 centimeters and a weight of 1650 kilograms; the aluminum-26 activity indicates a minimum exposure age of 3 million years. 相似文献
7.
Somayajulu BL 《Science (New York, N.Y.)》1967,156(3779):1219-1220
Analyses of beryllium-10 activity in two sections of a manganese nodule indicate an accumulation rate that compares well with such rates measured by other methods on different nodules. The observed specific activity of beryllium-10 in the nodule is in accord with the calculations based on the production of beryllium-10 by cosmic rays in the atmosphere and with the geochnemistry of beryllium in the ocean. 相似文献
8.
The Grenoble cyclotron has been used as a mass spectrometer to measure ratios of beryllium-10 to beryllium-9 of 10(-8), 10(-9), and 10(-10) in standardized beryllium oxide samples. Similar measurements can be used to determine cosmogenic beryllium-10 (half-life, 1.5 x 10(6) years) profiles in various geophysical reservoirs such as sea sediments and polar ice. This procedure can be used either to date such samples or to give information about geophysical and astrophysical phenomena that have influenced the beryllium-10 production rate in the past. 相似文献
9.
The cosmic-ray exposure age of the Farmington meteorite was found to be greater than 7000 years from the ratio of the carbon-14 and argon-39 present and less than 25,000 years from the ratio of the aluminum-26 and argon-39 present. This exposure age is about an order of magnitude smaller than was estimated previously. 相似文献
10.
Accurate terrestrial glacial chronologies are needed for comparison with the marine record to establish the dynamics of global climate change during transitions from glacial to interglacial regimes. Cosmogenic beryllium-10 measurements in the Wind River Range indicate that the last glacial maximum (marine oxygen isotope stage 2) was achieved there by 21,700 +/- 700 beryllium-10 years and lasted 5900 years. Ages of a sequence of recessional moraines and striated bedrock surfaces show that the initial deglaciation was rapid and that the entire glacial system retreated 33 kilometers to the cirque basin by 12,100 +/- 500 beryllium-10 years. 相似文献
11.
RP Scherer A Aldahan S Tulaczyk G Possnert H Engelhardt B Kamb 《Science (New York, N.Y.)》1998,281(5373):82-85
Some glacial sediment samples recovered from beneath the West Antarctic ice sheet at ice stream B contain Quaternary diatoms and up to 10(8) atoms of beryllium-10 per gram. Other samples contain no Quaternary diatoms and only background levels of beryllium-10 (less than 10(6) atoms per gram). The occurrence of young diatoms and high concentrations of beryllium-10 beneath grounded ice indicates that the Ross Embayment was an open marine environment after a late Pleistocene collapse of the marine ice sheet. 相似文献
12.
Each of seven Australasian tektites contains about 1 x l0(8) atoms of beryllium-10 (half-life, 1.53 x 10(6) years) per gram. Cosmic-ray bombardment of the australites cannot have produced the measured amounts of beryllium-10 either at the earth's surface or in space. The beryllium-10 contents of these australites are consistent with a sedimentary precursor that adsorbed from precipitation beryllium-10 produced in the atmosphere. The sediments must have spent several thousand years at the earth's surface within a few million years of the tektite-producing event. 相似文献
13.
The radioactivity of aluminum-26 in two cores of Pacific sediments is an order of magnitude higher than was expected, as a result of its production by cosmic-ray interactions in the terrestrial environment. The higher activity can be explained only by postulating influx with extraterrestrial cosmic dust that had been exposed to significant flux of energetic particles capable of producing nuclear interactions. These particles may well be the "solar" cosmic rays that are sporadically accelerated by Sun during certain solar flares, since the steady galactic cosmic-ray flux is inadequate. The long-term average flux of low-energy protons in interplanetary space, required to yield the observed rate of influx of aluminum-26, is deduced on the basis of certain assumptions. 相似文献
14.
Silicate grains from Tranquillity Base have shock-induced features ranging from internal fragmentation through complete disruption of the lattice to thermal melting. Half the crystalline grains with diameters less than 125 micrometers have features of shock equivalent to those produced in the laboratory at pressures greater than about 40 kilobars. One quarter have features indicative of pressures greater than 90 kilobars. These properties together with great quantities of melt glass and aluminum-26 in the fine-grained material are indicative of repeated shock-loading by meteoritic bombardment over long periods of time. 相似文献
15.
The global distribution of fluorocarbon-12 and fluorocarbon-11 is used to establish a relatively fast interhemispheric exchange rate of 1 to 1.2 years. Atmospheric residence times of 65 to 70 years for fluorocarbon-12 and 40 to 45 years for fluorocarbon-l1 best fit the observational data. These residence times rule out the possibility of any significant missing sinks that may prevent these fluorocarbons from entering the stratosphere. Atmospheric measurements of methyl chloroform support an 8-to 10-year residence time and suggest global average hydroxyl radical (HO) concentrations of 3 x 10(5) to 4 x 10(5) molecules per cubic centimeter. These are a factor of 5 lower than predicted by models. Additionally, methyl chloroform global distribution supports Southern Hemispheric HO levels that are a factor of 1.5 or more larger than the Northern Hemispheric values. The long residence time and the rapid growth of methyl chloroform cause it to be a potentially significant depleter of stratospheric ozone. The oceanic sink for atmospheric carbon tetrachloride is about half as important as the stratospheric sink. A major source of methyl chloride (3 x 10(12)grams per year), sufficient to account for nearly all the atmospheric methyl chloride, has been identified in the ocean. 相似文献
16.
Measurements of radon-222 in seawater suggest the following. The radium-226 content of surface water in both the Atlantic and Pacific oceans is uniformly close to about 4 x 10(-14) gram per liter. The deep Pacific has a concentration of radium-226 that is four times higher and the deep Atlantic a concentration twice as high as that of the surface. These distribution profiles can be explained by the same particle-settling rate for radium-226 from surface to depth for the two oceans and by a threefold longer residence time of water in the deep Pacific than in the deep Atlantic. The vertical distribution of the deficiency of radon-222 in the surface water of the northwest Pacific Ocean suggests a coefficient of vertical eddy diffusion as high as 120 square centimeters per second and a gas-exchange rate for carbon dioxide in surface water between 14 and 60 moles per square meter per year. Vertical profiles of the excess of radon-222 in near-bottom water of the South Atlantic give coefficients of vertical eddy diffusion ranging from 1.5 to more than 50 square centimeters per second. 相似文献
17.
S Baumgartner J Beer J Masarik G Wagner L Meynadier H Synal 《Science (New York, N.Y.)》1998,279(5355):1330-1332
Geomagnetic field strength is expected to affect the production rate of cosmogenic isotopes such as beryllium-10, carbon-14, or chlorine-36. Chlorine-36 data from the Greenland Ice Core Project (GRIP) ice core agree well with a production rate calculation based on a paleomagnetic reconstruction for the past 100,000 years over both long- and short-term variations. A chlorine-36 peak at 38,000 years ago previously found in the beryllium-10 record from the Vostok ice core can be explained by a period of low geomagnetic field intensity. 相似文献
18.
Diamond anvil presses of a new design were used to compress samples of beryllium-7 oxide to 120, 210, and 270 kilobars. The decay constant for the conversion of beryllium-7 to lithium-7 by electron capture was measured for compressed and uncompressed samples. A least-squares fit of the equation (lambda(c)-lambda)/lambda = KpP to the experimental data, where lambda(C) and lambda are the decay constants of the compressed sample and an uncompressed sample, respectively, and P is pressure, yields a value of (2.2 +/- 0.1) x 10(-5) kbar(-1) for the constant K(p). 相似文献
19.
Montagna P McCulloch M Taviani M Mazzoli C Vendrell B 《Science (New York, N.Y.)》2006,312(5781):1788-1791
Phosphorus is a key macronutrient being strongly enriched in the deep ocean as a result of continuous export and remineralization of biomass from primary production. We show that phosphorus incorporated within the skeletons of the cosmopolitan cold-water coral Desmophyllum dianthus is directly proportional to the ambient seawater phosphorus concentration and thus may serve as a paleo-oceanographic proxy for variations in ocean productivity as well as changes in the residence times and sources of deep-water masses. The application of this tool to fossil specimens from the Mediterranean reveals phosphorus-enriched bottom waters at the end of the Younger Dryas period. 相似文献
20.
Radiocarbon data from the Cariaco Basin provide calibration of the carbon-14 time scale across the period of deglaciation (15,000 to 10, 000 years ago) with resolution available previously only from Holocene tree rings. Reconstructed changes in atmospheric carbon-14 are larger than previously thought, with the largest change occurring simultaneously with the sudden climatic cooling of the Younger Dryas event. Carbon-14 and published beryllium-10 data together suggest that concurrent climate and carbon-14 changes were predominantly the result of abrupt shifts in deep ocean ventilation. 相似文献