Lunar and Planetary Science XXIX
1107.pdf
FATTY ACIDS AND GLYCOLAMIDE EXTRACTED FROM OLIVINE SINGLE CRYSTALS. 2A. Gupta 1 1,2 1 and F. Freund , SETI Institute at NASA Ames Research Center, MS 239-4, Moffett Field, CA 94035-1000, also at the Department of Physics, San Jose State University, and SETI Institute, e-mail:
[email protected].
We explore the possibility that complex organic molecules, in particular molecules in the system H–C– N–O, can be formed inside the hard, dense matrix of minerals in igneous rocks, cooled from magmatic temperatures. These H–C–N–O molecules derive from traces of structurally dissolved H2O and CO 2. The theoretical basis is well understood 1 . H2O and CO2 become incorporated as “impurities” in any minerals that crystallize in H2O and CO 2–laden environments. During cooling the solutes undergo an internal redox conversion whereby they split off H2 and reduced C. Such H 2 and C behave as incompatible “impurities”, i.e. they segregate to dislocations, subgrain boundaries and other major defects. The segregation concentrates H2 and the reduced C- and Nbearing species at the defect sites. As a consequence C-C, C-H and C-N bonds begin to form at the segregation sites besides C-O bonds, leading to HxC yNz Oknprecipitates in the mineral matrix. These H xC yNz Okn- precipitates have no idenfiable infrared signature because they remain strongly coupled to the surrounding matrix and give rise to very broad IR bands. However, they are the backbones of what will turn into organic molecules when the crystals are crushed and extracted with H2O. In nature, weathering is the global process by which the organics would be liberated. In our laboratory experiments we start with 10-20 mm sized upper mantle olivine crystals from San Carlos, AZ, gem-quality and optically clear. We clean these crystals externally by refluxing with chloroform to remove any outside contamination. We then crush them under clean conditions to a medium fine powder. The powder is subjected to a Soxhlet extraction either sequentially with chloroform, acetone and tetrahydrofuran (THF) or with H 2O. The organics extracted are analyzed by FT-IR and by GC-MS using an HP 5971 with a capillary column and a 5890 data station. The chloroform extracts were directly injected, the THF and H2O extracts were injected after tertiarybutyldimethylsilyl (t-BDMS) derivatization. Table I shows the assignment of GC-MS peaks of CH 2=CHterminated alkyls extracted with chloroform, and Table II shows identification of one selected GC peak of the H2O extract by assigning the MS fragments. In addition, of course, to be alerted to any contamination that might be inadvertently introduced in the laboratory, we follow the standard practice of full procedural blanks. No such contamination was detected.
Table I Mass fragments in chloroform extract CH2=CH + amu CH3–CH2+ CH2=CH-CH2+ CH3–CH2-CH2+ or CH 3CO+ CH2=CH-CH2- CH2+ CH3–CH2-CH2-CH2+ or CH 3-CH2CO+ CH2=CH-CH2-CH2-CH2+ CH3–CH2-CH2-CH2-O+ or CH 3-CH2COO+ CH2=CH-CH2-CH2- CH2-CH2+ CH3–CH2-CH2-CH2-CH2-O+ or CH 3-CH2-CH2COO+ CH2=CH-CH2-CH2- CH2-CH2-CH2+ CH2=CH-CH2-CH2- CH2-CH2- CH2-CH2+ CH2=CH-CH2-CH2- CH2-CH2- CH2-CH2-CH2+ CH2=CH-CH2-CH2- CH2-CH2- CH2-CH2- CH2-CH2+ CH2=CH-CH2-CH2- CH2-CH2- CH2-CH2- CH2-CH2- CH2+
27 29 41 43 55 57 69 73 83 87 97 111 125 139 153
Given the small amounts of extractable organics, contamination is of great concern. Contamination in the field may have penetrated into microcracks inaccessible to external chloroform cleaning. To guard ourselves against such field contamination we take chunks of the vesicular basalt that had brought the olivine–bearing peridotite nodules from depth in the course of a volcanic eruption. Being highly vesicular with many cracks and a large surface area onto which biogenic organics could have adsorbed, the basalt is much more receptive than any of the gem-quality olivine crystals to biogenic field contamination. While the vesicular basalt was found to be essentially devoid of extractable organics and mostly yielded carbonate, the extraction experiments with the crushed olivine crystals yield a rich spectrum of organic compounds, including monocarboxylic “fatty” acids, H3C–(CH2)n–COOH with n ranging from 6 to 10. Such short to medium length fatty acids are distinct from biogenic fatty acids. We also identified at least one N-bearing compound of the composition C 2H5NO2, glycolamide, H2COH–CO–NH2, which is identical to the glycolamide reported by Cooper & Cronin2 from the Murchison meteorite. Furthermore, we identified a series of C2 to C 4 carboxylic and dicarboxylic acids (glycolic, oxalic, malonic, succinic acids) in THF extracts from crushed, laboratory-grown MgO crystals 3 plus urea, (NH2) 2CO. To our knowledge this is the first time that longchain hydrocarbons, fatty acids and at least one Nbearing organic compound have been identified in extracts from olivine crystals from the upper mantle. These results corroborate our working hypothesis1 that organics derive from common fluid-phase components H2O, CO 2 and N2 that become structurally dissolved in the mineral matrix and subsequently undergo
Lunar and Planetary Science XXIX
1107.pdf
FATTY ACIDS AND GLYCOLAMIDE EXTRACTED FROM OLIVINE: A. Gupta and F. Freund
a series of internal reactions that lead to segregation of H2, C and N to defect sites and formation of Hx C y NnzOk precipitates. O CH3 CH3
H3C
(H 2C) 6
C
Si
O
C
CH 3
CH3 CH3
M-15
CH3
O H 3C
(H2 C)6
C
CH 3 CH 3 O
Si
C
CH 3 CH 3 CH3
M-42
C CH3 O H3C
(H 2C) 6
C
CH3 O
Si
CH3 Table II : GC peak crystals at RT 8.3 min of the derivatized H 2O extract from the olivine crystals gives a mass spectrum with major fragments at 201 and 243 amu which can be identified as fragments from to the mono-tBDMS derivative of C8 monocarboxylic acid. The total quantity of extractable organics is difficult to assess. Using crushed olivine crystals we have access to only those HxC yNz Okn- precipitates that are on the freshly formed fracture surfaces. Most fractures will have followed the mechanically weak subgrain boundaries, preferentially exposing the H xC yNz Oknprecipitates, but more similarly decorated subgrain boundaries and dislocations are not accessible unless the whole crystals disintegrate like in the course of weathering. A cautious estimate of the total amount of organics yields 5-50 wt.-ppm. Our results lay to rest earlier claims by Mathez, Tingle and coworkers 4, 5, 6 that the organics in olivine from peridotite nodules are just coatings formed by volcanic gases undergoing unspecified catalytic reactions on the walls of microfractures that temporarily opened and closed during ascent in the volcanic vent. Our findings have implications for understanding the origin of Life on Earth and on other Earth-like
planets. The geological record suggests that the early Earth was already tectonically active, meaning that large quantities of mafic and ultramafic rocks were uplifted and subjected to massive surface weathering. Surely, the structurally dense minerals in those rocks contained the same type of HxC yNz Okn- precipitates as the upper mantle-derived olivine crystals which we study today. Therefore, early rocks must have been a source of complex H–C–N–O organics liberated through global weathering. The rock-derived abiogenic organics may have been essential ingredients in the "soup" from which Life sprang. If such a process occurred on Earth, it is likely to have also taken place on Earth-like planets in the habitable zones around other stars, endowed with internal engines to drive tectonics and with surface water to set up a global weathering cycle. On Mars, where global tectonics apparently did not develop, complex organics may still have been leached from the shattered rocks of the deep regolith by volcanically or impact–driven circulating groundwater. References 1 F. Freund, Hydrogen and carbon in solid solution in oxides and silicates, Phys. Chem. Minerals 15 (1987): 1-18. 2 G.W. Cooper, and J.R. Cronin, Linear and cyclic aliphatic carboamides of the Murchison meteorite: Hydrolyzable derivatives of amino acids and other carboxyli acids, Geochim. cosmochim. Acta 59.5 (1995): 1003-1015. 3 F. Freund, A. Gupta, and D. Kumar, Organic matter from H2O and CO 2 dissolved in minerals, Lunar and Planetary Science Conference, (Houston: Lunar Planetary Institute, 1996) 27: 379-380. 4 E. A. Mathez et al., "Carbon in olivine: results from nuclear reaction analysis," J. Geophys. Res. 92 (1987): 3500-3506. 5 T.N. Tingle et al., "Organic compounds on crack surfaces in olivine from San Carlos, Arizona, and Haulalai Volcano, Hawaii," Geochim. Cosmochim. Acta 54 (1990): 477-485. 6 T.N. Tingle, E.A. Mathez, and M.F. Hochella, "Carbonaceous matter in peridotites and basalts studied by XPS, SALI, and LEED.," Geochim. Cosmochim. Acta 55 (1991): 1345-1352. Acknowledgments: We thank G.W. Cooper for valuable advise and the NASA Exobiology Program for support of this work.
