Allan Hills

Meteorite ALH84001 was found in the Allan Hills in Antarctica in 1984 and was the subject of an extraordinary NASA press announcement in 1996. It weighed 1.93 kg when it was collected (Figure 6.10) and is probably the most extensively studied lump of rock of all time. It is 95 per cent orthopyroxene, the volcanic rock mineral that accumulated in a molten-lava-reducing environment on Mars some... 

Figure 1 is a map of Antarctica showing the locations of Byrd Station, Allan Hills, and other well-marked sites. 

Table 1 except the Allan Hills surface sample from stake 12,... 

The pH of Antarctic ice is 5.5. The first three samples that were studied (362 and 363 m Byrd core and Allan Hills surface ice from stake 12) were acidified before purging. 

Essentially the same amino acids, and nearly equal quantities of D and L enantiomers, were detected in the Murray meteorite, another type II carbonaceous chondrite [6]. Recent expeditions to Antarctica have returned with a large number of meteorites, many of which are carbonaceous chondrites. These may have been protected from terrestrial contamination by the pristine Antarctic ice. Careful analysis of two of these, the Yamato (74662) and the Allan Hills (77306), both type II carbonaceous chondrites, by ion exchange chromatography, gas chromatography, and GC/MS, have detected a wide variety of both protein and non-protein amino acids in approximately equal D and L abundances [9,10]. Fifteen amino acids were detected in the Yamato meteorite and twenty in the Allan Hills, the most abundant being glycine and alanine. The amino acid content of the Yamato meteorite is comparable with that of the Murchison and Murray, but the Allan Hills contains 1/5 to 1/10 that quantity. Unlike earlier meteorites from other locations, the quantities of amino acids in the exterior and interior portions of the Yamato and Allan Hills meteorites are almost identical [9,10]. Thus, these samples may have been preserved without contamination since their fall in the blue ice of Antarctica, which js 250,000 years old in the region of collection. 

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... 

Figure 5. Photomosaics of the cathodoluminescence of three intermediate petrologic type meteorites (a) Chainpur (type 3.4, top), (b) Allan Hills A77214 (type 3.4, middle), and (c) Ngawi (host predominantly type 3.6 containing clasts of type 3.1, bottom). With increasing petrologic type, the diversity of CL properties within a meteorite decreases, red luminescent material becomes scarce and blue material becomes more abundant.

Figure 11. Two glow curves for the type 3.4 ordinary chondrite Allan Hills A77011 (which may actually be a fragment of the same meteorite as Allan Hills A77214) before and after annealing at 900°C for 200 h in a dry nitrogen atmosphere at atmospheric pressure. (Reprinted by permission from Ref. 33. Copyright 1984 MacMillan Journals.)...

Figure 12. Plot of peak temperature against peak width for samples of Allan Hills A77214 annealed in a dry nitrogen atmosphere at atmospheric pressure, and at the temperatures indicated, for 100 h. Type 3 ordinary chondrites (c.f. Figure 3) are plotted as dots. (Reprinted with permission from Ref. 9. Copyright 1985 Pergamon Press.)...

Schultz L., Palme H., Spettel B., Weber H. W., Wanke H., Christophe Michel-Levy M., and Lorin J. C. (1982) Allan Hills A77081—an unusual stony meteorite. Earth Planet. Sci. Lett. 61, 23-31. 

Scott E. R. D. (1988) A new kind of primitive chondrite, Allan Hills 85085. Earth Planet. Sci Lett. 91, 1-18. 

Warren P. H. and Kallemeyn G. W. (1989) Allan Hills 84025 the second Brachinite, far more differentiated than Brachina and an ultramafic achondritic clasts from L chondrite Yamato 95097. Proc. Lunar Planet Sci. Conf 19, 475-486. 

Wasson J. T. and Kallemeyn G. W. (1990) Allan Hills 85085 a subchondritic meteorite of mixed nebular and regolithic heritage. Earth Planet Sci. Lett 101, 148—161. 

Hanowski N. P. and Brearley A. J. (2000) Iron-rich aureoles in the CM carbonaceous chondrites, Murray, Murchison, and Allan Hills 81002 evidence for in situ aqueous alteration. Meteorit. Planet. Sci. 35, 1291-1308. 

Hua X., Wang J., and Buseck P. R. (2002) Pine-grained rims in the Allan Hills 81002 and Lewis Cliff 90500 CM2 meteorites their origin and modification. Meteorit. Planet. Sci. 37, 229-244. 

Grossman J. N., Rubin A. E., and MacPherson G. J. (1988) Allan Hills 85085 a unique volatile-poor carbonaceous chondrite with implications for nebular agglomeration and fractionation processes. Earth Planet. Sci. Lett. 91, 33-54. 

Eugster O. and Niedermann S. (1990) Solar noble gases in the unique chondritic breccia Allan Hills 85085. Earth Planet. Sci. Lett. 101, 139-147. 

Jull A. J. T., Coutney C., Jeffrey D. A., and Beck J. W. (1998) Isotopic evidence for a terrestrial source of organic compounds found in martian meteorites Allan Hills 84001 and Elephant Moraine 79001. Science 279, 366-369. 

Figure 10 Deep clastic dike in a coal of the Weller Coal Measures of the Allan Hills, Antarctica, interpreted as infill of periglacial polygonal patterned ground (E. S. Krull and hammer for scale).

Whether formed from acetylene or from some other sources, PAHs are widely distributed in the solar system. As mentioned earlier, PAHs are found in the atmospheres of Jupiter and Titan [37]. They have also been detected in meteorites, including the Martian meteorite Allan Hills 84001 [43], in interplanetary dust [44], and in circumstellar graphite grains [45]. The ubiquity of these complex organic structures and their stability under extreme conditions is a significant factor in discussions of the origin of life on earth and the possibility of its existence elsewhere. 

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