Creating an isotopically similar Earth–Moon system with correct angular momentum from a giant impact     

Bryant M. Wyatt  Jonathan M. Petz  William J. Sumpter  Ty R. Turner  Edward L. Smith  Baylor G. Fain  Taylor J. Hutyra  Scott A. Cook  John H. Gresham  Michael F. Hibbs  Shaukat N. Goderya 《Journal of Astrophysics and Astronomy》2018,39(2):26

The giant impact hypothesis is the dominant theory explaining the formation of our Moon. However, the inability to produce an isotopically similar Earth–Moon system with correct angular momentum has cast a shadow on its validity. Computer-generated impacts have been successful in producing virtual systems that possess many of the observed physical properties. However, addressing the isotopic similarities between the Earth and Moon coupled with correct angular momentum has proven to be challenging. Equilibration and evection resonance have been proposed as means of reconciling the models. In the summer of 2013, the Royal Society called a meeting solely to discuss the formation of the Moon. In this meeting, evection resonance and equilibration were both questioned as viable means of removing the deficiencies from giant impact models. The main concerns were that models were multi-staged and too complex. We present here initial impact conditions that produce an isotopically similar Earth–Moon system with correct angular momentum. This is done in a single-staged simulation. The initial parameters are straightforward and the results evolve solely from the impact. This was accomplished by colliding two roughly half-Earth-sized impactors, rotating in approximately the same plane in a high-energy, off-centered impact, where both impactors spin into the collision.  相似文献   

The Gulf of Maine boundary: Dropping anchor or setting a course?     

Ted L. McDorman  Phillip M. Saunders  David L. VanderZwaag 《Marine Policy》1985,9(2):90-107

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Late Holocene relative sea level rise and the Neoglacial history of the Greenland ice sheet     

Antony J. Long  Sarah A. Woodroffe  Sue Dawson  David H. Roberts  Charlotte L. Bryant 《第四纪科学杂志》2009,24(4):345-359

In West Greenland, early and mid Holocene relative sea level (RSL) fall was replaced by late Holocene RSL rise during the Neoglacial, after 4–3 cal. ka BP (thousand calibrated years before present). Here we present the results of an isolation basin RSL study completed near to the coastal town of Sisimiut, in central West Greenland. RSL fell from 14 m above sea level at 5.7 cal. ka BP to reach a lowstand of ?4.0 m at 2.3–1.2 cal. ka BP, before rising by an equivalent amount to present. Differences in the timing and magnitude of the RSL lowstand between this and other sites in West and South Greenland record the varied interplay of local and non‐Greenland RSL processes, notably the reloading of the Earth's crust caused by a Neoglacial expansion of the Greenland Ice Sheet (GIS) and the subsidence associated with the collapse of the Laurentide Ice Sheet forebulge. This means that the timing of the sea level lowstand cannot be used to infer directly when the GIS advanced during the Neoglacial. The rise in Late Holocene RSL is contrary to recently reported bedrock uplift in the Sisimiut area, based on repeat GPS surveys. This indicates that a belt of peripheral subsidence around the current ice sheet margin was more extensive in the late Holocene, and that there has been a switch from subsidence to uplift at some point in the last thousand years or so. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

The surface of Mars: Michael H. Carr. Yale University Press,New Haven and London, 1984. 236 pp., $24.95     

Ted A. Maxwell 《Icarus》1985,63(1):179-180

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The hydrochemistry of a semi-arid pan basin case study: Sua Pan,Makgadikgadi, Botswana     

Frank D. Eckardt  Robert G. Bryant  Graham McCulloch  Baruch Spiro  Warren W. Wood 《Applied Geochemistry》2008

This study presents results on the fluid and salt chemistry for the Makgadikgadi, a substantial continental basin in the semi-arid Kalahari. The aims of the study are to improve understanding of the hydrology of such a system and to identify the sources of the solutes and the controls on their cycling within pans. Sampling took place against the backdrop of unusually severe flooding as well as significant anthropogenic extraction of subsurface brines. This paper examines in particular the relationship between the chemistry of soil leachates, fresh stream water, salty lake water, surface salts and subsurface brines at Sua Pan, Botswana with the aim of improving the understanding of the system’s hydrology. Occasionally during the short wet season (December–March) surface water enters the saline environment and precipitates mostly calcite and halite, as well as dolomite and traces of other salts associated with the desiccation of the lake. The hypersaline subsurface brine (up to TDS 190,000 mg/L) is homogenous with minor variations due to pumping by BotAsh mine (Botswana Ash (Pty) Ltd.), which extracts 2400 m³ of brine/h from a depth of 38 m. Notable is the decrease in TDS as the pumping rate increases which may be indicative of subsurface recharge by less saline water. Isotope chemistry for Sr (⁸⁷Sr/⁸⁶Sr average 0.722087) and S (δ³⁴S average 34.35) suggests subsurface brines have been subject to a lithological contribution of undetermined origin. Recharge of the subsurface brine from surface water including the Nata River appears to be negligible.  相似文献   

Radon transfer from groundwater used in showers to indoor air     

David S. Vinson  Ted R. Campbell  Avner Vengosh 《Applied Geochemistry》2008

Estimation of Rn transfer from water to indoor air based on multi-day measurements may underestimate alpha exposure that occurs at short time scales in confined spaces, such as from showering, in houses with high Rn activities in the water supply. In order to examine one such incremental increase in exposure, variations in Rn in water and indoor air in 18 houses with private wells in western North Carolina (USA) were investigated. Radon in well water ranged from 158 to 811 Bq L⁻¹ (median 239 Bq L⁻¹). After 20-min showers in bathrooms with closed doors, peak Rn in air increases (above background) ranged from 71 to 4420 Bq m⁻³ (median 1170 Bq m⁻³). Calculated transfer coefficients at the scale of a 40-min closed bathroom (20-min shower plus 20 min post-shower) are described by a lognormal distribution whose geometric mean exceeds the widely-used ∼10⁻⁴ whole-house transfer coefficient by about one order of magnitude. As short-lived decay products grow from shower-derived Rn, short-term alpha energy exposure occurs in bathrooms in addition to the exposure caused by Rn mixed throughout the volume of the house. Due to the increasing ratio of Rn decay products to Rn, alpha energy exposure is greatest several minutes after the shower is turned off. For a 7.2-min shower with 10 min of additional exposure before opening the door, a geometric mean 5.6% increase in exposure over the ∼10⁻⁴ whole-house transfer coefficient derived from longer measurement periods was estimated. In addition to Rn activity in water, short-term shower exposure to Rn progeny depends on exposure time, ventilation, attachment and deposition, among other variable factors that characterize individual houses and residents.  相似文献   

Environmental overview of Eckernförde Bay,northern Germany     

T. H. Orsi  F. Werner  D. Milkert  A. L. Anderson  W. R. Bryant 《Geo-Marine Letters》1996,16(3):140-147

This environmental overview of Eckernförde Bay (northern Germany) summarizes the results of previous studies relevant to the Office of Naval Research's Coastal Benthic Boundary Layer (CBBL) Baltic field exercise conducted during 1993–1994. Significant environmental characteristics include the following: (1) surface sediment distribution is related to water depth, dictated primarily by hydrodynamic reworking of older glacial deposits; (2) the origin and characteristics of small-scale sedimentary structures depend on storm-generated waves and currents; (3) the proximity of the sea surface and sediment —water interface results in a pelagic—benthic coupling that drives biogeochemical processes and produces organicrich, acoustically turbid sediments; and (4) the bay floor is complicated topographically by pockmarks and manmade sedimentary structures.  相似文献   

Geology of the lunar farside crater Necho   总被引：1，自引：0，他引：1  

Ann W. Gifford  Ted A. Maxwell  Farouk El-Baz 《Earth, Moon, and Planets》1979,21(1):25-42

The lunar farside crater Necho (30 km diameter) displays intricate morphological and structural characteristics. The highland setting provides a complex impact site when compared with the relatively uniform setting of mare craters. Therefore, the effects of pre-impact topography and structure play a dominant role in Necho's formation and modification. Necho's bright ejecta, extensive rays, fresh morphology, and lack of superposed craters indicate that it is extremely young. The asymmetric distribution of ejecta materials may be due to substrate effects, topographic shalowing, or oblique impact.Necho's interior is divided into five physiographic units based on morphologic differences: three floor units (Necho does not display a true flat floor), one hilly central unit, and the wall unit which includes terraces and smooth walls. The interior of the crater also exhibits an unusual asymmetry in the prevalence of terraced units on the western wall. Interior morphology and terrace orientations are probably the result of pre-impact effects. Structural and topographic orientations associated with three large pre-existing degraded craters dominate the impact site.  相似文献   

Beyond the impasse: the power of political ecology in Third World environmental research   总被引：3，自引：0，他引：3  

Raymond L Bryant 《Area》1997,29(1):5-19

Summary In the context of a deepening impasse in Third World environmental research, this paper suggests that researchers should adopt a political ecology perspective to ensure that research addresses the political and economic issues that underlie the Third World's environmental problems. Since an understanding of unequal power relations is central to political ecology, the paper considers how questions of power influence human-environmental interaction, before assessing briefly how research of this kind might contribute to a resolution of the Third World's environmental problems.  相似文献   

The multiple chronological techniques applied to the Lake Suigetsu SG06 sediment core,central Japan     

Richard A. Staff  Takeshi Nakagawa  Gordon Schlolaut  Michael H. Marshall  Achim Brauer  Henry F. Lamb  Christopher Bronk Ramsey  Charlotte L. Bryant  Fiona Brock  Hiroyuki Kitagawa  Johannes van der Plicht  Rebecca L. Payne  Victoria C. Smith  Darren F. Mark  Alison Macleod  Simon P. E. Blockley  Jean‐Luc Schwenninger  Pavel E. Tarasov  Tsuyoshi Haraguchi  Katsuya Gotanda  Hitoshi Yonenobu  Yusuke Yokoyama  Suigetsu Project Members 《Boreas: An International Journal of Quaternary Research》2013,42(2):259-266

The varved sediment of Lake Suigetsu (central Japan) provides a valuable opportunity to obtain high‐resolution, multi‐proxy palaeoenvironmental data across the last glacial/interglacial cycle. In order to maximize the potential of this archive, a well‐constrained chronology is required. This paper outlines the multiple geochronological techniques being applied – namely varve counting, radiocarbon dating, tephrochronology (including argon–argon dating) and optically stimulated luminescence (OSL) – and the approaches by which these techniques are being integrated to form a single, coherent, robust chronology. Importantly, we also describe here the linkage of the floating Lake Suigetsu (SG06) varve chronology and the absolute (IntCal09 tree‐ring) time scale, as derived using radiocarbon data from the uppermost (non‐varved) portion of the core. This tie‐point, defined as a distinct (flood) marker horizon in SG06 (event layer B‐07–08 at 1397.4 cm composite depth), is thus derived to be 11 255 to 11 222 IntCal09 cal. years BP (68.2% probability range).  相似文献