Lithosphere/rocks rock cycle

The phenomena described above are parts of the tectonic cycle, a geological cycle that describes how tectonic plates move relative to each other, magma rises to form new solid rocks, and solid lithospheric rocks sink to become melted, thus forming new magma. The tectonic cycle is illustrated in Figure 17.2. 

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. 

Carbon. Most of the Earth s supply of carbon is stored in carbonate rocks in the Hthosphere. Normally the circulation rate for lithospheric carbon is slow compared with that of carbon between the atmosphere and biosphere. The carbon cycle has received much attention in recent years as a result of research into the possible relation between increased atmospheric carbon dioxide concentration, most of which is produced by combustion of fossil fuel, and the "greenhouse effect," or global warming. Extensive research has been done on the rate at which carbon dioxide might be converted to cellulose and other photosyntheticaHy produced organic compounds by various forms of natural and cultivated plants. Estimates also have been made of the rate at which carbon dioxide is released to soil under optimum conditions by various kinds of plant cover, such as temperature-zone deciduous forests, cultivated farm crops, prairie grassland, and desert vegetation. 

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. 

Carbon-12 is a stable isotope and is by far the most abundant isotope of carbon found on Earth. Carbon-13 is also stable but occurs on Earth only as a very small proportion of the total carbon. Carbon is found in large quantities in the atmosphere (mostly as COj, the most abundant atmospheric gas after N, O, Ar, and water vapor), the lithosphere (especially in rocks, like limestone, that contain the carbonate ion (CO 3 ), and the hydrosphere (as dissolved CO and as H COj, HCO3, and COl ). Carbon is constantly cycling through the air, water, and rocks on Earth, as well as through living organisms, since carbon is the basis of life as we know it. 

For simplicity, igneous phosphate rock is defined as rock formed when primary primitive magma cooled. It will be assumed that most of the igneous phosphate rock of Earth has been igneous phosphate rock since the lithosphere first cooled and has not been through more than one heating and cooling cycle. This is surely not true in all cases, but is approximately correct. 

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