Composition of earth’s crust

Explain why a line graph might not be appropriate to show the chemical composition of Earth s crust. 

Why does the composition of Earth s crust differ so greatly from that of its core ... 

The composition of Earth s crust and that of the human body are significantly different. The numbers represent percentages by mass in each. The elements oxygen and hydrogen are found in both, but carbon is concentrated in living things. 

Can you name two significant differences between the elemental composition of Earth s crust and the elemental composition of the human body ... 

Three major types of rocks are found in Earth s crust igneous rocks, formed by solidification of molten rock (e.g., basalt) sedimentary rocks (e.g., sandstone, which is cemented sand), formed by deposition of dissolved or suspended substances from oceans and rivers and metamorphic rocks (e.g., marble), formed by the action of heat and pressure on existing rocks. Figure 18.2 gives the average composition of Earth s crust. The most abundant substances in rocks are silicates, which are composed of silicon, oxygen, and positive metal ions (Section 18.5). The more than 2000 kinds of known minerals fall into a few major classes (Table 18.1). 

Many scientists thought that Earth must have formed as long as 3.3 billion years ago, but their evidence was confusing and inconsistent. They knew that some of the lead on Earth was primordial, i.e., it dated from the time the planet formed. But they also understood that some lead had formed later from the radioactive decay of uranium and thorium. Different isotopes of uranium decay at different rates into two distinctive forms or isotopes of lead lead-206 and lead-207. In addition, radioactive thorium decays into lead-208. Thus, far from being static, the isotopic composition of lead on Earth was dynamic and constantly changing, and the various proportions of lead isotopes over hundreds of millions of years in different regions of the planet were keys to dating Earth s past. A comparison of the ratio of various lead isotopes in Earth s crust today with the ratio of lead isotopes in meteorites formed at the same time as the solar system would establish Earth s age. Early twentieth century physicists had worked out the equation for the planet s age, but they could not solve it because they did not know the isotopic composition of Earth s primordial lead. Once that number was measured, it could be inserted into the equation and blip, as Patterson put it, out would come the age of the Earth. ... 

In contrast to their rather low dissolved concentrations in seawater, some of the trace metals, e g., iron and aluminum, along with oxygen and silicon, comprise the bulk of Earth s crust. Some trace elements are micronutrients and, hence, have the potential to control plankton species composition and productivity. This provides a connection in the crustal-ocean-atmosphere fectory to the carbon cycle and global climate. 

With these restrictions, almost 4,000 different minerals are known, with several dozen new minerals identified each year. Every mineral possesses a combination of chemical composition and crystal structure that makes it unique, and by which it is classified (grouped with similar minerals) and identified. These minerals make up the solid Earth, the moon, and even meteorites. However, only 20 or so minerals compose the bulk of Earth s crust, that is, the part of the solid Earth accessible to human beings, extending from the surface downward to a maximum depth of about 55 mi (90 km). These minerals are often called the rock-forming minerals. 

Table 17.2. Comparison of cosmic composition and earth s crust The fourth column is from Cox, P. A. (1997). The Elements. Oxford Oxford University Press. The second and third columns are derived...

Estimates of the chemical composition of Earth s mantle normally refer to the composition of the Earth s mantle as it existed immediately after core formation but before the extraction of the continental crust. This composition is known as the bulk silicate Earth (BSE) or the Primitive mantle and is an important reference composition for the study of the mantle. 

The most complete and reliable data about the chemical composition of the Venusian surface comes from three Soviet missions, the Venera 13, Venera 14, and Vega 2 probes. These spacecraft actually reached the planet s surface and conducted studies of elements and compounds present on the planet s surface. In atypical experiment, one of the lander s tools would drill a hole into the planet s surface about 1.2 inches (3 cm) deep and extract a sample about 1 cm3 in volume. The chart on page 110 summarizes data obtained from these three missions and gives the composition of Earth s continental crust for purposes of comparison. Notice that the major differences in crustal composition between the two planets appears to be in the relative abundance of Si02 (45.6 percent on Venus compared with 60.2 percent on Earth) and of MgO (about 11.5 percent on Venus compared with 3.1 percent on Earth). Otherwise, the two planets do indeed appear to be almost "sister planets," at least with regard to the composition of their outer crusts. 

TWO PRINCIPAL TYPES of Earth s crusts have formed. These are the oceanic and the continental crusts that differ in composition, age, and evolution. The oceanic crust is effectively a conveyor belt that transfers the chemical elements, derived from melting in the mantle beneath the mid-ocean ridges, to the plate margins where they are subducted back down into the mantle. The composition is dominated by basalts with a veneer of sediment derived from biological activity in the oceans and weathering of the continents. Intraplate basaltic volcanoes from a deeper mantle source that involves some of the subducted oceanic crust, make a minor contribution to the oceanic crust. 

The Composition of Earth s Upper Crust, Natural Cycles of Elements, Natural Resources... 

Composition of the Earth s Crust, Seawater, and the Human Body ... 

Table 8-2 Elemental composition by atoms of the Earth s crust"...

By far the most abundant phosphate mineral is apatite, which accounts for more than 95% of all P in the Earth s crust. The basic composition of apatite is listed in Table 14-2. Apatite exhibits a hexagonal crystal structure with long open channels parallel to the c-axis. In its pure form, F , OH , or Cl occupies sites along this axis to form fluorapatite, hydroxyapatite, or chlor-apatite, respectively. However, because of the "open" nature of the apatite crystal lattice, many minor substitutions are possible and "pure" forms of apatite as depicted by the general formula in Table 14-2 are rarely found. 

The average composition of the Earth s crust is essentially the composition of igneous rocks. 

Clarke FW, Washington HS 1924) The composition of the earth s crust. US Geological Survey Professional Paper 127,117 pp. 

Present attention is focussed on the lithosphere which is the solid part of the Earth s crust. Details as regards its components and composition are shown in Table 1.2. It is... 

In the previous paragraph, it has been stated that minerals have the same structure but different compositions (phenomenon of isomorphism of minerals) while some minerals have the same composition but different structures (phenomenon of polymorphism of minerals). Mineral composition and structure are both important in studying and classifying minerals. The major class of minerals - based on composition and structure - include elements, sulfides, halides, carbonates, sulfates, oxides, phosphates, and silicates. The silicate class is especially important, because silicon makes up 95% of the minerals, by volume, in the Earth s crust. Mineral classes are divided into families on the basis of the chemicals in each mineral. Families, in turn, are made of groups of minerals that have a similar structure. Groups are further divided into species. 

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