Elements from terrestrial

Percentage of meteorites seen to fall. Chondrites. Over 90% of meteorites that are observed to fall out of the sky are classified as chondrites, samples that are distinguished from terrestrial rocks in many ways (3). One of the most fundamental is age. Like most meteorites, chondrites have formation ages close to 4.55 Gyr. Elemental composition is also a property that distinguishes chondrites from all other terrestrial and extraterrestrial samples. Chondrites basically have undifferentiated elemental compositions for most nonvolatile elements and match solar abundances except for moderately volatile elements. The most compositionaHy primitive chondrites are members of the type 1 carbonaceous (Cl) class. The analyses of the small number of existing samples of this rare class most closely match estimates of solar compositions (5) and in fact are primary source solar or cosmic abundances data for the elements that cannot be accurately determined by analysis of lines in the solar spectmm (Table 2). Table 2. Solar System Abundances of the Elements ... 

Extraterrestrial dust particles can be proven to be nonterrestrial by a variety of methods, depending on the particle si2e. Unmelted particles have high helium. He, contents resulting from solar wind implantation. In 10-)J.m particles the concentration approaches l/(cm g) at STP and the He He ratio is close to the solar value. Unmelted particles also often contain preserved tracks of solar cosmic rays that are seen in the electron microscope as randomly oriented linear dislocations in crystals. Eor larger particles other cosmic ray irradiation products such as Mn, Al, and Be can be detected. Most IDPs can be confidently distinguished from terrestrial materials by composition. Typical particles have elemental compositions that match solar abundances for most elements. TypicaUy these have chondritic compositions, and in descending order of abundance are composed of O, Mg, Si, Ee, C, S, Al, Ca, Ni, Na, Cr, Mn, and Ti. 

All substances containing isotopes (i.e., elements of mixed isotopic composition) must have S0 0, because the isotopic variants are again distributed randomly through the crystalline lattice. Practically all elements of the periodic table are known to be composed of terrestrial mixtures of two or more isotopes, so the intrinsic isotopic randomness must lead to residual S0 7 0 in practically every imaginable compound formed from terrestrial elements. 

Chondrites. Over 909, of the meteorites lhat are observed lo fall out of the sky are classified as chondrites, samples lhat are distinguished from terrestrial rocks in many ways. One of the most fundamental is age. Like most meteorites, chondrites have formation ages close to 4.55 Gyr. Chondrites also have basically undifferentiated elemental compositions lor most nonvolatile elements and match solar abundances except for moderately volatile elements. The imtsl cunipositionally primitive chondrites are members for the type I carbonaceous f Cl I class. 

Many fertilisers for the treatment of deficiencies of trace elements are added to the leaves. In addition, uptake of trace elements from aerial sources through the leaves may have a significant impact on plant contamination, especially of elements such as Fe, Mn, Zn and Cu. Anthropogenic aerosols have been reported to bring about foliar deposition of Pb to a great extent (Streit and Stumm, 1993). Zieve and Peterson (1984) have reported the assimilation of diemethyl selenide through leaves of terrestrial plants. Roberts et al. (1975) found a significant absorption of foliar-applied Zn, Fe, Cd and Mg. 

Minor element contents and isotopic ratios are used for physiological purposes. Sr/Ca ratios in bone and teeth are said to reflect the diet of the animal (herbivores versus carnivores). Stable isotope analysis of teeth and bones provides direct information on the lifetime diets the nitrogen isotopes reflect the trophic level of the protein that has been consumed. Within an ecosystem, they can identify herbivores and carnivores, while the carbon isotopes tell mainly about the amount of protein in the diets from terrestrial versus marine ecosystems. 

The elements of the chondritic meteorites, and hence of the terrestrial planets, were formed in previous generations of stars. Their relative abundances represent the result of the general chemical evolution of the galaxy, possibly enhanced by recent local additions from one or more specific sources just prior to collapse of the solar nebula —4.56 Gyr ago. A volumetrically minor, but nevertheless highly significant part of this chemical inventory, is comprised of radioactive elements, from which this age estimate is derived. The famihar long-lived radionuclides, such as Th, Rb, K, and others,... 

Like nitrates, phosphates are included in the indicative list of main pollutants (Water Framework Directive, 2000/60/EC) because of their contribution to eutrophication. Phosphorus is an essential nutrient for all plants and in modem agriculture this element has to be supplied to the crops as fertilizer. Wind erosion, surface mnoff and leaching constitute the main pathways for transport of phosphoms from terrestrial to aquatic ecosystems. The process is accelerated by agriculture, animal husbandry and anthropogenic discharges. 

The natural global bio-geochemical cycling of mercury is characterized by degassing of the element from soils and surface waters, followed by atmospheric transport, deposition of mercury back to land and surface waters, and sorption of the compound to soil or sediment particulates. Mercury deposited on land and open water is in part revolatilized back into the atmosphere. This emission, deposition, and revolatilization creates difficulties in tracing the movement of mercury to its sources (WHO 1990). Particulate-bound mercury can be converted to insoluble mercury sulfide and precipitated or bioconverted into more volatile or soluble forms that re-enter the atmosphere or are bioaccumulated in aquatic and terrestrial food chains (EPA 1984b). 

Humic substances are from terrestrial sources in overlying soils. Humic substances in the Biscayne aquifer are quite similar to those in surface water in elemental analysis, carbohydrate content, color, molecular weight, C/... 

Neutral hydroxide Si(OH)4 is predominant in the natural water, the content of anion Si(0H)30 is in a lesser degree. The continental river water discharge is responsible for 0.2 x 10 tons of soluble silicon species. The mass of Si compounds in the ocean is 4, 110 x 1tons, and the residence time of Si in the marine waters is 20,550 years. The transport of silicon from terrestrial to oceanic ecosystems is not counterbalanced by the reverse transport. In addition to the soluble species, the content of silicon in river particulate matter is about 120 /rg/L. This gives the elemental transport of 4.8 x 10 tons/yr. The total estimate of river water fluxes from the global land area to the ocean is 5.0 x 10 tons/yr. Aeolian migration of silicon is responsible for 0.47 X 10 tons per year. It means the annual global land losses (river and wind fluxes) are 5.47 x 10 tons (Dobrovolsky, 1994). 

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