Lithosphere/rocks weathering

Let us now determine the functional and dynamic characteristics of the fluxes of phosphorus (Table 4.4) based on analysis of existing ideas about their nature. The atmospheric cycle is governed by rock weathering, volcanic eruptions, and by the leaching of phosphorus by precipitation. From available estimates, the content of phosphorus in the lithosphere constitutes 0.093%, and the processes of weathering deliver annually to the atmosphere from 0.67 mgPcm 3 yr 1 to 5.06mgPcm-3 yr-1. Every year, volcanic eruptions contribute to the atmosphere about 0.2 106 tP. Since these processes are complicated and stochastic in nature and their models are absent, as a first approximation fluxes H and //f9 can be considered constant. 

Aluminum, a silver-white, malleable, and ductile metal, is the most abundant metallic element in the lithosphere, comprising about 8% of the earth s crust. It is never found free in nature, but occurs combined with other elements, most commonly as aluminosilicates, oxides, and hydroxides in rock, minerals, clays, and soil. It is also present in air, water, and many foods. Bauxite, a weathered rock consisting primarily of aluminum hydroxide minerals, is the primary ore used in aluminum production. Aluminum enters environmental media naturally through the weathering of rocks and minerals. Anthropogenic releases are in the form of air emissions, waste water effluents, and solid waste primarily associated with industrial processes, such as aluminum production. Because of its prominence as a major constituent of the earth s crust, natural weathering processes far exceed the contribution of releases to air, water, and land associated with human activities. 

There were times on our planet when the barren dryness of uninhabited continents sharply contrasted with the densely populated sea. The continental lithosphere was then essentially represented by rock surfaces of different types. Sedimentary rocks were rare, if not absent. As rock materials became exposed to the subaerial environment at the Earth s surface, they encountered a whole range of environmental challenges such as temperature fluctuations, water, unbuffered cosmic and solar irradiation and atmospheric gases and solids instead of dissolved species. These influences resulted in rocks undergoing alterations in material properties leading to erosion and breakdown into ever-smaller particles and constituent minerals, formation of sandy sediments, and mineral soils (Ehrlich, 1996). Primordial terrestrial environments can therefore be visualized as a freshly exposed and only slightly physically pre-weathered rock surface. 

Some rocks have a natural porosity and, at the interface of the atmosphere and the lithosphere and given the presence of moisture, all rocks tend to weather to a relatively porous soil. In the simplest case, the pore spaces of soil are occupied by atmospheric air, but the very moisture that enhances soil formation is also highly supportive of flora and fauna, which interact with the air in the pores and modify its composition. 

The whole-rock Rb-Sr date of 1789 141 Ma (Paleoproterozoic) is the time when these rocks were recrystallized during regional metamorphism to amphibolite grade and the strontium they contained was isotopically homogenized so that all three specimens had the same initial Sr/ Sr ratio of 0.7059 0.0041. This value indicates that their protoliths contained strontium derived from the lithospheric mantle in the form of volcanic rocks or their weathering products. 

The flow of matter from continents to oceans and to the ocean floor is obviously visible it is frequently termed exogenous or minor cycle . It describes the transfer of matter from the lithosphere to the hydrosphere and then back to the lithosphere. It is questionable whether a fragment of weathered rock, either crystalline or sedimentary in origin, moving in streams is part of the lithosphere. 

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