نتایج جستجو برای: weathering resistance
تعداد نتایج: 381072 فیلتر نتایج به سال:
It has been proposed that increased rates of chemical weathering and the related drawdown of atmospheric CO on the 2 Ž . continents may have at least partly contributed to the low CO concentrations during the last glacial maximum LGM . 2 Variations in continental erosion could thus be one of the driving forces for the glacialrinterglacial climate cycles during Quaternary times. To test such an ...
A model for the combined long-term cycles of carbon and sulfur has been constructed which combines all the factors modifying weathering and degassing of the GEOCARB III model [Berner R.A., Kothavala Z., 2001. GEOCARB III: a revised model of atmospheric CO2 over Phanerozoic time. Am. J. Sci. 301, 182–204] for CO2 with rapid recycling and oxygen dependent carbon and sulfur isotope fractionation o...
–Carbon bound in gibbsite, collected from a residual weathering profile developed on a Paleozoic granite in the Georgia Piedmont, was examined for its C content and found to be geologically young. The study site, located at the Panola Mountain Research Watershed, has developed a granite–saprolite–soil regolith in which C-gibbsite model ages deep within the profile (C-horizon) average about 8000...
As chemical weathering of silicate rocks acts as a sink for atmospheric CO2 and as greenhouse effect gases such as CO2 have a leading role in climate regulation, much of river geochemical studies now focus on chemical and mechanical riverine erosion and on their controlling parameters. Moreover, weathering has probably had a dominating influence in the climatic evolution of the Earth, and studi...
Mitochondrial DNA analysis of skeletal material is invaluable in forensic identification, although results can vary widely among remains. Previous studies have included bones of different ages, burial conditions, and even species. In the research presented, a collection of human remains that lacked major confounders such as burial age, interment style, and gross environmental conditions, while ...
The weathering hypothesis states that teen childbearing among African American women is rationalized given greater early exposure to poor physical health and shortened life spans that result from the physical consequences of social inequality in African American communities (i.e., “weathering”). This paper tests a simple yet unexplored test of the basic assumption of the weathering hypothesis: ...
Fossil and phylogenetic evidence indicates legume-rich modern tropical forests replaced Late Cretaceous palm-dominated tropical forests across four continents during the early Cenozoic (58-42 Ma). Tropical legume trees can transform ecosystems via their ability to fix dinitrogen (N2) and higher leaf N compared with non-legumes (35-65%), but it is unclear how their evolutionary rise contributed ...
We tested antlers of Coues white-tailed (Odocoileus virginianus couesi) and mule deer (O. hemionus) in various stages of natural decomposition to determine the degree of weathering that cast antlers could endure and still yield usable DNA. Based on physical characteristics, we partitioned antlers into 7 weathering categories ranging from freshly cast (class 1) to having been exposed to weatheri...
Critical Zone (CZ) research investigates the chemical, physical, and biological processes that modulate the Earth's surface. Here, we advance 12 hypotheses that must be tested to improve our understanding of the CZ: (1) Solar-to-chemical conversion of energy by plants regulates flows of carbon, water, and nutrients through plant-microbe soil networks, thereby controlling the location and extent...
The heliocentric stratification of asteroid spectral types may hold important information on the early evolution of the Solar System. Asteroid spectral taxonomy is based largely on principal component analysis. However, how the surface properties of asteroids, such as the composition and age, are projected in the principal-component (PC) space is not understood well. We decompose multi-band dis...
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