Stratified Earth

Earth is stratified, as is well known, and its resistivity varies significantly at the top layer depending on the weather and climate. The earth-return impedance of an overhead conductor above the stratified earth was derived in Ref. [16], and the stratified-earth effect was investigated in Ref. [17]. The stratified-earth effect might be far more significant than the accurate evaluation of the homogenous earth-return impedance of Pollaczek and Carson, and this requires a further investigation. 

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Nakagawa, M., A. Ametani, and K. Iwamoto. 1973. Further studies on wave propagation in overhead lines with earth return—Impedance of stratified earth. Proc. lEE 120(2) 1521-1528. 

Besides these features, the formation of a layer due to an interaction of a stratified fluid with light is itself noteworthy. Analogs to this phenomenon can be found in other media. Examples include photochemical reactions in the atmosphere near the Earth s surface, photochemical reactions in the surface water of the ocean and biological activity near the ocean surface. 

The chemical composition of the Lower Mantle below 670 km is essentially unknown. It has often been assumed to be the same as the Upper Mantle with the seismic discontinuity at 670 km representing a phase change to denser polymorphs rather than a chemical boundary (Liu and Bassett, 1986). However, some models of the Earth s interior suggest that the Mantle is stratified with the Upper Mantle and Lower Mantle convecting separately, leading to compositional density differences between these two regions. There is a commonly held view that the Lower Mantle has a higher Fe/(Mg+Fe) ratio than the Upper Mantle (Liu and Bassett, 1986 Jeanloz and Knittle, 1989). 

Before assessing how a chemical moves in the environment, the relevant media, or compartments, must be defined. The environment can be considered to be composed of four broad compartments—air, water, soil, and biota (including plants and animals)—as shown in Fig. 6.6. Various approaches to modeling the environment have been described.14-16 The primary difference in these approaches is the level of spatial and component detail included in each of the compartments. For example, the most simplistic model considers air as a lumped compartment. A more advanced model considers air as composed of air and aerosols, composed of species such as sodium chloride, nitric and sulfuric acids, soil, and particles released anthropogenically.17 A yet more complex model considers air as composed of air in stratified layers, with different temperatures and accessibility to the earth s surface, and aerosols segmented into different size classes.16 As the model complexity increases, its resolution and the data demands also increase. Andren et al.16 report that the simplest of models with lumped air, water, and soil compartments is suitable for... 

The present consensus is that the modern Earth s continental cmst has a bulk andesitic composition (—61% Si02), but it is lithologically and chemically stratified, such that a mafic... 

As the plane continues to climb, the ride becomes smooth. Coffee served in open cups does not spill, providing testimony that in the tropopause [at approximately 10,000 m (33,000 ft)] and the still higher stratosphere (Fig. 4-1), the size and energy of atmospheric eddies decrease. Weather phenomena are confined almost entirely to the troposphere. Being at the edge of the stratosphere is comparable to being in the thermocline of a stratified lake (Section 2.2.2) turbulent diffusion is suppressed, and vertical Fickian transport is slowed. Chemicals released into the air near Earth s surface may mix... 

Virtually all (99.999%) of the mass of the earth s atmosphere lies within 80 km of its surface 80% is within the lowest 12 km. The atmosphere is not a region of smoothly varying properties, but is distinctly stratified. 

Sediments on the surface of the Earth may form in several ways (1) by mere mechanical accumulation (via wind or water), such as gravel and sand deposits in a river or sand dunes in a desert (2) by chemical precipitation, such as salt and calcite precipitation in shallow seas and lakes and (3) by activity of organisms, such as carbonate accumulation in coral reefs or the accumulation of organic matter in swamps (coal precursor). Sediments are typically deposited in layers or beds called strata. When sediments become compacted and cemented together (a process known as lithification), they form sedimentary rocks. This compaction or lithification of sedimentary materials into stratified layers is probably the most significant feature of sedimentary rocks. 

These stratified layers are like pages in the ultimate history book—Earth s history— where each page is dedicated to a particular time frame, earliest to present. Sediments of any particular time period form a distinct layer that is underlain and overlain by equally distinct layers of older and younger times, respectively. These layers, composed of such common rock types as sandstone, shale, and limestone, make up about 75% of the rocks exposed on the surface of the Earth. Geologists can study sedimentary rocks in the making therefore, they probably know more about the origin of this type of rock than igneous and metamorphic rocks combined. 

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