Meteorites Allan Hills

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. 

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... 

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.)...

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. 

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. 

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. 

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. 

Stolper E, Paque JM (1986) Crystalhzation sequences of Ca-Al-rich inclusions from Allende The effects of coohng rate and maximum termperatrrre. Geochim Cosmochim Acta 50 1785-1806 Sugiitra N, Hoshino H (2000) Hydrogen-isotopic compositions in Allan Hills 84001 and the evolution of the martian atmosphere. Meteoritics Planet Sci 35 373-380 Taylor HP, Jr., Epstein S (1970) 18-0/16-0 ratios of Apollo 11 lunar rocks and soils. Proc Apollo 11 Lunar Sci Conf, p 1613-1626... 

Porcelli D, Ballentine CJ (2002) Models for the distribution of terrestrial noble gases and the evolution of the atmosphere. Rev Mineral Geochem 47 411-480 Sears D, Scott E, Warren P (1997) The legacy of Allan Hills 84001. Meteoritic Planet Sci 33 545-546 Shih C-Y, Nyquist LE, Reese Y, Wiesmann H (1998) The chronology of the nakhhte, Lafayette Rb-Sr and Sm-Nd isotopic ages. Lunar Planet Sci XXIV, Abstr 1145 (CD-ROM)... 

Tanaka KL, Scott CH, Greeley R (1992) Global stratigraphy. In Mars. Kieffer HH, Jakosky BM, Snyder CW, Matthews MS (eds) Univ of Arizona Press, Tucson, p 345-382 Treiman AH (1995) Multiple source areas for Martian meteorites. J Geophys Res 100 5329-5340 Treiman AH (1998) The histoiy of Allan Hills 84001 revised Multiple shock events. Meteoritic Planet Sci 33 753-764... 

The ablation rates of ice within the Reckling Moraine and in the surrounding ice fields were determined by Faure and Buchanan (1991). The results in Table 17.4 also include ablation rates of the main ice field adjacent to the Allan Hills where several hundred meteorite specimens have been recovered by personnel of Project ANSMET (Antarctic Search for Meteorites) (Score and Lindstrom 1990). 

A final point to be made is that the spherules must have been deposited on the surface of the East Antarctic ice sheet, which means that East Antarctica was glaciated at the time (i.e., two to three million years ago). Therefore, the terrestrial age of the meteorite-ablation spherules is consistent with the evidence that Cenozoic volcanoes in the Transantarctic Mountains (e.g., Mt. Early and Sheridan Bluff) erupted through glacial ice from which it follows that the glaciation of East Antarctica started during the late Oligocene/early Miocene perhaps as early as 25 million years ago. However, none of the ice cores that have been drilled in East or West Antarctica have encountered ice that is as old as the meteorite ablation spherules in the icefield near the Allan Hills. 

The ice fields adjacent to the Allan Hills, where a large number of meteorite specimens have been collected, also contain tephra layers. The outcrop patterns of these layers indicate that the ice was extensively deformed as it flowed over and around the subglacial foothills of the Transantarctic Mountains. A small deposit of black spherules embedded in the ice near the Allan Hills was attributed to the passage through the atmosphere of a stony meteorite. This deposit reminds us that the East Antarctic ice sheet contains extraterrestrial particles and specimens of meteorites in addition to terrigenous dust and volcanic ash. 

Marvin UB (1990) Diverse components of dust bands in Allan Hills ice samples. In Cassidy WA, WhiUans IM (eds) Workshop on Antarctic meteorite stranding Surfaces. LPI Tech. Rept., vol. 90-03. Lunar and Planetary Institute, Houston, TX, pp 75-79... 

Scherer P et al (1997) Allan Hills 88019 an Antarctic H-chondrite with a very long terrestrial age. Meteoritics Planet Sci 32 769-773... 

The meteorites recovered by Japanese scientists from 1966 to 1994 were listed by Yanai and Kojima (1995) who also provided chemical analyses of a large number of specimens that originated from the Yamato Mountains, Asuka Station, Sor Rondane Mountains, Allan Hills, Bates Nunatak, Derrick Peak, and Mt. Baldr. Three of the specimens listed by Yanai and Kojima (1995) are lunar meteorites Asuka-881757, Yamato-793274, and Yamato-793169. The compilation includes color photographs of 12 specimens of different kinds of stony meteorites including A-881757 from the Moon. 

Fig. 18.5 Cross-section of the East Antarctic ice sheet west of the Allan HiUs in southern Victoria Land according to the ice-flow model of Whilltins and Cassidy (1983). The model predicts that the terrestrial ages of meteorite specimens that are transported by the ice sheet tmd tire released when the ice sublimates in the ablation area should decrease with increasing distance west of the Allan Hills. Adapted from Whillans and Cassidy (1983). The view is to the north with west on the left and east on the right. The vertical exaggeration is lOOx (Adapted from WhUlans and Cassidy 1983)...

The Allan Hills are a relatively small group of sandstone and dolerite ridges on the edge of the polar plateau at 74°43 S and 159°40 E. The East Antarctic ice sheet adjacent to the Allan Hills in Fig. 18.10 contains several areas of blue ice where meteorite specimens have accumulated which are identified by the indicated letter codes (Appendix 18.12.1) ... 

The progress in the recovery of ALH meteorites is recorded in Fig. 18.11. The spikes in the number of specimens collected identify the field seasons during which ANSMET carried out systematic searches in the blue-ice areas of the Allan HiUs. The last major harvest during 1988/89 consisted of the 163 specimens that were collected by members of GANOVEX. The specimens collected in the 1976/77,1977/78, and 1978/79 fieldseasons on the Allan Hills icefields were split and the USA and Japan shared half of each specimen. The catalog of Score and Lindstrom (1990) Usts the original masses of these specimens, whereas Yanai and Kojima (1995) recorded the masses of the splits that were transferred to the National Institute of Polar Research (NIPR) in Tokyo, Japan. 

Fig. 18.11 During the 1976/77 field season a joint American-Japanese team collected nine meteorite specimens on the Main ice field adjacent to the Allan Hills. Subsequently, systematic searches by ANSMET yielded large numbers of specimens until the 1988/89 season when a team of American and German investigators collected additional specimens. More recently, geological field parties working in the area have continued to recover small numbers of additional specimens. The process that caused the ALH meteorite specimens to accumulate on the stranding surfaces of this area is continuing to deliver new specimens as the ice continues to ablate at the rate of about 5 cm/year (Data from Score and Lindstrom 1990, and from recent issues of the Antarctic Meteorite Newsletter)...

Table 18.5 Classification of meteorite specimens collected on the ice fields adjacent to the Allan Hills that carry the code ALH. Based on data from Score and Lindstrom (1990). Note that the abundances of the ALH meteorite specimens are similar to those of falls and differ from the abundances of finds ...

The meteorite specimens collected on the icefields of the Allan Hills include at least three rocks from Mars and one from the Moon. In addition, the collection includes rare specimens of certain achondrites and other... 

The histogram of the terrestrial ages of meteorite specimens collected on the Allan-Hills ice fields in Fig. 18.16 demonstrates that more than 35% of the specimens that have been dated fell less than 100,000 years ago and that about 10% have been on the Earth for more than 5(X),(XX) years, including ALH88019... 

Fig. 18.16 The terrestrial ages of stony and iron meteorites from the ice fields adjacent to the Allan Hills range from <100 x lO to 2,200 X 10 years. All dates were calculated from the rate of decay of cosmogenic Q in metallic Fe-Ni-Co grains measured by means of accelerator mass spectrometry (Data from Nishiizumi et al. 1989 Michlovich et al. 1995 Scherer et at 1997)...

---