Meteorites martian

When considering how the evolution of life could have come about, the seeding of terrestrial life by extraterrestrial bacterial spores traveling through space (panspermia) deserves mention. Much is said about the possibility of some form of life on other planets, including Mars or more distant celestial bodies. Is it possible for some remnants of bacterial life, enclosed in a protective coat of rock dust, to have traveled enormous distances, staying dormant at the extremely low temperature of space and even surviving deadly radiation The spore may be neither alive nor completely dead, and even after billions of years it could have an infinitesimal chance to reach a planet where liquid water could restart its life. Is this science fiction or a real possibility We don t know. Around the turn of the twentieth century Svante Arrhenius (Nobel Prize in chemistry 1903) developed this theory in more detail. There was much recent excitement about claimed fossil bacterial remains in a Martian meteorite recovered from Antarctica (not since... 

The anomalous micro-composition of the Martian atmosphere with regard to nitrogen, argon, neon, krypton and xenon has also been compared with trapped gases for the Martian meteorite collection (12 in total). The isotope ratios for... 

Becker L. et al. (1999). The origin of organic matter in the Martian meteorite ALH84001. 

Bogard D. D. and Garrison D. H. (1998). Relative abundances of argon, krypton, and xenon in the Martian atmosphere as measured in Martian meteorites. Geochimica et Cosmochimica Acta, 62(10) 1829-1835. 

Gibson Jr E. K. et al. (2001). Fife on Mars evaluation of the evidence within Martian meteorites ALH84001, Nakhla and Shergotty, Precabrian Research 106 15-34. 

As is the case for hydrogen, carbon isotope signatures in Martian meteorites present evidence for different carbon reservoirs. Wright et al. (1990) and Ro-manek et al. (1994) distingnished three carbon compounds one component released... 

McKay DS, et al. (1996) Search for past life on Mars possible relic biogenic activity in martian meteorite ALH 84001. Science 273 924-930... 

Valley JW, EUer JM, Graham CM, Gibson EK, Romanek CS, Stolper EM (1997) Low temperature carbonate concretions in the martian meteorite ALH 84001 evidence from stable isotopes and mineralogy. Science 275 1633-1637... 

Biogenic magnetite may persist once the organism that produced it has died and may, therefore, contribute to the natural magnetic remanence of sediments (Stolz et al., 1986). The discovery in a calcareous Martian ( ) meteorite found in Antarctica, of magnetite crystals with properties very similar to these biogenic magnetites, sup-... 

Comparison of trapped gases in impact-melt glass in the EET 79001 Martian meteorite with the composition of the Martian atmosphere as measured by Viking landers. This remarkable agreement is the evidence that convinced most planetary scientists that SNC meteorites came from Mars. 

Photomicrograph of the ALH84001 Martian meteorite, field of view = 1.3 cm. Large, broken grains of pyroxene form this breccia. This sample created a stir when it was proposed to contain evidence for extraterrestrial life. Image from Lauretta and Kilgore (2005), with permission. 

Martian meteorites ( SNC for shergottite, nakhlite, chassignite) comprise a diverse suite of igneous rocks (McSween, 2004). With only one exception, they are geologically young. Presently, 34 of these meteorites are recognized, most recovered from Antarctica and North African deserts. 

Martian meteorites, viewed in plane polarized light with FOV = 5.4 mm. (a) Zagami basaltic shergottite, composed of pyroxene and plagiodase (white), which has been converted to maskelynite by shock, (b) Lafayette nakhlite, composed mostly of high-calcium pyroxene, (a) from Lauretta and Killgore (2005), with permission. 

ALHA 84001 is a unique Martian meteorite with an ancient age of 4.5 billion years. It consists mostly of orthopyroxene crystals that accumulated in basaltic magma. Its most distinctive feature, however, is the occurrence of small globules of carbonates with unusual compositions and textures. The controversial (now largely discredited) hypothesis that the carbonates contain evidence of extraterrestrial life (McKay et al., 1996) made this the most famous meteorite on Earth. ALHA 84001 has also experienced intense shock metamorphism. 

We will return to a more detailed consideration of the chemistry of Martian meteorites in Chapter 13 and of their chronology in Chapter 9. 

Plots of uranium versus lanthanum (two refractory elements), and potassium versus lanthanum (a volatile element and a refractory element) for terrestrial and lunar basalts, HED achondrites (Vesta), and Martian meteorites. All three elements are incompatible elements and thus fractionate together, so their ratios remain constant. However, ratios of incompatible elements with different volatilities ( /La) reveal different degrees of volatile element depletion in differentiated bodies. After Wanke and Dreibus (1988). 

Ion microprobe analyses of hydrous minerals in Martian meteorites reveal two different sources of hydrogen. One is interpreted as magmatic water, with 5D = 900 permil, and thought to reflect the mantle composition the other is thought to reflect the atmospheric composition, with 5D =4000 permil (Leshin, 2000). The incorporation of atmospheric water into these meteorites suggests some kind of cycling of water between the atmosphere and lithosphere on Mars. 

Sulfur isotopes also show mass-independent effects that are probably produced by the same photochemical mechanism as oxygen effects in the Earth s upper atmosphere. Mass independent variations in sulfur from Martian meteorites have been interpreted to result from volcanic injections of SO2 and H2S into the Martian atmosphere followed by photolysis, which fractionates the sulfur isotopes. There is also evidence from ancient terrestrial sediments that the same photo lytic process was operating on sulfur in the Earth s atmosphere prior to 2.4 Ga, before oxygen began to accumulate in the atmosphere (see review by Thiemens, 2006). 

Leshin, L. A. (2000) Insights into Martian water reservoirs from analyses of Martian meteorite QUE 94201. Geophysical Research Letters, 27, 2017-2020. 

Nyquist, L. E., Bogard, D. D., Shih, C.-Y. et al. (2001b) Ages and geologic histories of Martian meteorites. Space Science Reviews, 96, 105-164. 

Constraints on the accretion and differentiation of Mars come from the application of four isotopic systems to Martian meteorites ... 

There are significant differences in the 142Nd and e182W values obtained for the different types of Martian meteorites (Fig. 9.15). These variations indicate that the meteorites were derived from distinct mantle reservoirs that were established early in the history of Mars. Modeling based on s l42Nd and e182W indicates that differentiation of the silicate mantle could have taken place contemporaneously with core formation or could have been... 

Information on the igneous history of Mars is given by the crystallization ages of Martian meteorites (Nyquist el al., 2001 Borg and Drake, 2005). The only ancient Martian meteorite... 

Summary of radiometric ages for Martian meteorites. After Borg and Drake (2005). 

Borg and Drake (2005) have determined the timing of aqueous alteration events in Martian meteorites from the ages of secondary minerals. Carbonates in ALH 84001 formed at 3.9 Ga, iddingsite in nakhlites formed -630 Myr ago, and salts in shergottites formed sometime after the crystallization of these rocks, 170 Myr ago. 

Ejection ages (sum of cosmic-ray exposure age + terrestrial age) for Martian meteorites. The ages cluster by meteorite type, suggesting that each cluster represents a distinct impact (ejection) event. The only outliers are the EETA 79001 and Dhofar 019 shergottites and ALHA84001. Modified from McSween (2008). 

What is the evidence that Martian meteorites came to Earth as a result of a few discrete impact events on the Martian surface ... 

Kleine, T., Mezger, K., Mtinker, C., Palme, H. andBischoff, A. (2004) Hf- W isotope systematics of chondrites, eucrites, and Martian meteorites chronology of core formation and early mantle differentiation in Vesta and Mars. Geochimica et Cosmochimica Acta, 68, 2935-2946. 

McSween, H. Y. (2008) Martian meteorites as crustal samples. In I he Martian Surface Composition, Mineralogy, and Physical Properties, ed. Bell, J. E, III. Cambridge Cambridge University Press, pp. 383-396. 

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