Meteoritic find

The largest class of meteorite finds is stony meteorites, made principally of stone. The general stony classification is divided into three subclasses called chondrites, carbonaceous chondrites and achondrites, and it is at this level of distinction at which we will stop. Before looking at their mineral and isotopic structure in more detail, it is useful to hold the composition of the Earth s crust in mind here for comparison. The Earth s crust is 49 per cent oxygen, 26 per cent silicon, 7.5 per cent aluminium, 4.7 per cent iron, 3.4 per cent calcium, 2.6 per cent sodium, 2.4 per cent potassium and 1.9 per cent magnesium, which must have formed from the common origin of the solar system. 

Figure 4 Ne exposure ages of LL chondrites. Ne ages recalculated with the formulas of Eugster (1988). Multiple analyses for meteorites were averaged. Meteorite finds from Antarctica and northern Africa with similar exposure ages and collected at the same site were treated as paired (source L. Schultz).

Meteorites are superficially described as being either falls or finds. A meteorite fall is scientifically more useful than a find because the exact time that it hit Earth s surface is known. Einds, on the other hand, are simply that—meteorites that have been found by chance. The largest meteorite find fo date is fhaf of the 66-ton (60-metric ton) Hoba meteorite in South Airica. Meteorites are either named after the recific geographic location in which they fall, or after the nearest postal station to the site of the fall. 

Lee, M.R. Bland, P.A. (2003) Dating climatic change in hot deserts using desert varnish on meteorite finds. Earth and Planetary Science Letters 206, 187-198. 

Meteorites are generally classified into two categories falls and finds. A meteoritic fall occurs when an observer actually sees a meteorite fall to Earth and is able to track and recover the meteorite. The term meteoritic find is used to describe a meteorite that has been found on Earth s surface, although there is no evidence as to when it fell to Earth. In one summary of meteorites, reported in The Handbook of Iron Meteorites, 55 percent of all discoveries were falls and 45 percent finds. 

Primarily iron and nickel and similar in composition to M-type asteroids iron, 91% nickel, 8.5% cobalt, 0.6%. A recent find of an iron meteorite on the surface of Mars is shown on p. 7 of the colour plate section... 

Chemical analysis of meteorites proceeds along classical analytical chemistry lines but with added precautions to prevent terrestrial contamination. Careful laboratory procedures have been developed, together with blank trials to enable the contamination in the laboratory to be eliminated. However, there is always the possibility of terrestrial contamination associated with the period of time on the ground before the find , in particular ice-melt water in the case of ALH84001. This meteorite... 

Observations from meteorite falls suggest that organic compounds that may be prebiotic are available in a concentrated form within meteorite samples. Hot-water washes and other extraction processes show the production of many of the compounds required for life. Most importantly from the ALH84001 find is that material can be moved between planetary bodies and organic molecules can be transported... 

Meteorite A meteoroid entering the atmosphere that survives the journey through the atmosphere to land on the ground and become a find . 

Another recent interesting finding is that previously unknown organic polymers or "amorphous carbon," which are noble gas carriers in meteorites, are actually carbynes. Five different carbynes have been identified in the Murchison and Allende carbonaceous... 

The basic idea in radioactive age-dating of rocks (from the Earth, Moon and meteorites) is to find the ratio of daughter to parent in an isolated system. Thus the age inferred is usually the solidification age which is the time since the last occasion when chemical fractionation was halted by solidification. (K-Ar dating gives a gas-retention age which can be slightly shorter.)... 

The question as to the potential availability of the requisite amphiphilic precursors in the prebiotic environment has been addressed experimentally by Deamer and coworkers, [143,145] who looked into the uncontaminated Murchison chondrite for the presence of such amphiphilic constituents. Samples of the meteorite were extracted with chloroform-methanol and the extracts were fractionated by thin-layer chromatography, with the finding that some of the fractions afforded components that formed monomolecular films at air-water interfaces, and that were also able to self-assemble into membranous vesicles able to encapsulate polar solutes. These observations dearly demonstrated that amphiphiles plausibly available on the primitive Earth by meteoritic infall have the ability to self-assemble into the membranous vesides of minimum protocells. ... 

Artificial hydrothermal vents might be constructed and supplied with plausible concentrations of simple reactants such as CO, H2, NH3, and H2S. Appropriate levels of amino adds induding a small chiral excess, along with the sorts of amphiphilic molecules described above, can be rationalized by the findings from the Murchison meteorite. Organic molecules such as found in irradiated interstellar ice models, including HMT, can also be induded. The system should indude weathered feldspars, which can be modified to indude the reduced transition-metal minerals that they are known to contain. [134] Such minerals as Fe,Ni sulfides are likely to have been both present and stable in the environment of early Earth and are known [153, 155] to catalyze formation of organic molecules from simpler precursors. 

Extremely stringent lower limits were reported by Rank (29) in 1968. A spectroscopic detection of the Lyman a(2 p - 1 s) emission line of the quarkonium atom (u-quark plus electron) at 2733 A was expected to be able to show less than 3 108 positive quarks, to be compared with 1010 lithium atoms detected by 2 p - 2 s emission at 6708 A. With certain assumptions (the reader is referred to the original article), less than one quark was found per 1018 nucleons in sea water and 1017 nucleons in seaweed, plankton and oysters. Classical oil-drop experiments (with four kinds of oil light mineral, soya-bean, peanut and cod-liver) were interpreted as less than one quark per 1020 nucleons. Whereas a recent value (18) for deep ocean sediments was below 10 21 per nucleon, much more severe limits were reported (30) in 1966 for sea water (quark/nucleon ratio below 3 10-29) and air (below 5 10-27) with certain assumptions about concentration before entrance in the mass spectrometer. At the same time, the ratio was shown to be below 10 17 for a meteorite. Cook etal. (31) attempted to concentrate quarks by ion-exchange columns in aqueous solution, assuming a position of elution between Na+ and Li+. As discussed in the next section, cations with charge + 2/3 may be more similar to Cs+. Anyhow, values below 10 23 for the quark to nucleon ratio were found for several rocks (e.g., volcanic lava) and minerals. It is clear that if such values below a quark per gramme are accurate, we have a very hard time to find the object but it needs a considerably sophisticated technique to be certain that available quarks are not lost before detection. 

Equation 11.118 finds practical application in cosmological studies and in geology (dating of sulfide deposits and sediments). Figure 11.27A shows, for instance, the Re-Os isochron for iron meteorites and the metallic phase of chondrites, obtained by Luck and Allegre (1983). The fact that all samples fit the same isochron within analytical uncertainty has three important cosmological implications ... 

The Allende, Murchison, Murray and Orgueil meteorites are particularly highly prized for research into stellar grains, since several kilograms of this material have been identified in each of them. This is sufficient to be able to take samples of the order of 1 g without damaging the source. Such samples can then be subjected to compositional analysis. But how can we extract these stellar jewels, measuring at most 1 /rm in diameter, from the matrix in which they are embedded The best way of finding a needle in a haystack is to bum the hay. Cosmochemists employ basically the same method when they use chemical processes to isolate star dust trapped in meteoritic stone. They may then analyse... 

Ganguly et al. (1994) found that an opx crystal from a meteorite has the above overall composition with Fe(M1) = 0.0060, and Mg(M1) = 0.9730. Find T e. Then find the cooling rate (in °C per million years) at Tae and compare it with the result of Ganguly et al. (1994). There may be a difference. If you need other information, consult the original work of Ganguly et al. (1994) or Zhang (1994). 

For many years, cosmochemistry depended on the chance discovery of meteorites - either witnessed falls and serendipitous finds, or the dogged determination of a few private collectors who systematically searched for them. That changed in 1969, when Japanese explorers in Antarctica led by Masaru Yoshida stumbled onto meteorites exposed on bare ice. American geologist William Cassidy immediately recognized an opportunity, and with support from the National Science Foundation he mounted a joint expedition with the Japanese to the Allan Hills region of Antarctica in 1977 to recover meteorites. This was the first of many expeditions, sponsored by the National Science Foundation and headed first by Cassidy and later by Ralph Harvey, that have returned to Antarctica every year to collect meteorites (Fig. 1.11). The Japanese have operated a parallel field program in... 

A large number of meteorites have been collected from hot desert areas. In these areas, rainfall is low, which helps to preserve the meteorites. In addition, the dry conditions make meteorites easier to find because vegetation is scarce and the wind blows away the fine dust, leaving rocks and meteorites as a lag deposit. 

De Laeter, J. R., in The History of Meteoritics and Key Meteoritic Collections Fireballs, Falls and Finds,... 

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