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The presence of magnetite crystal chains in ALH84001 was demonstrated by high-power …


Biology Articles » Astrobiology » Chains of magnetite crystals in the meteorite ALH84001: Evidence of biological origin » Figures

Figures
- Chains of magnetite crystals in the meteorite ALH84001: Evidence of biological origin

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Fig. 1.   (A and B) SEM-SE stereo micrograph of area in Fig. 4A, showing surface features. (C) SEM-BSE image of magnetosome chain in freeze-dried culture of Magnetospirillum magnetotacticum. (D and E) SEM-BSE stereo micrograph of A and B. (F) Outlines of areas shown in G and H and J and K. (I and L) Chains visible in G and H and J and K, respectively, are highlighted. px, orthopyroxene; ca, carbonate.

Figure 1

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Fig. 2.   Total energy [W(kT)], in units of thermal energy kT of a magnetite crystal chain plotted against the angle between the first and last particle of the chain, as calculated according to Eq. 8 in Appendix 1, which is published as supplementary material on the PNAS web site, www.pnas.org. For the case of soft gap fillings, the total energy is the sum of magnetic energy (Eq. 8) and elastic energy (Eq. 10). The energetically preferred deformation mode (lower value of W) is bending (a) for soft gap fillings and kink formation (b) for rigid gap fillings. Number of particles in chain n = 5; particle size a = 50 nm; length/width ratio = 1.4; gap space qa = 10 nm; Young modulus of soft material E = 0.1 MPa (106 dyn·cm-2). kT = 4 × 10-14 J.

Figure 2

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Fig. 3.   SEM-BSE micrographs of resin-embedded and polished specimens of rim regions of carbonate globules. (A) Lobes of a carbonate globule (ca) surrounded by plagioclase glass (pg) and orthopyroxene (px); arrow: site of E. (B) Magnetite chain with uniform gaps between particles. (C-E) Magnetite chains with strong bends; the S-shaped structure in D (arrows) may be composed from two chains. (F) Chain of elongated particles aligned along their long axes.

Figure 3

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Fig. 4.   (A-C) SEM-BSE micrographs of magnetite crystals in the rim region of carbonate globules in ALH84001. (A) Imaged through the intact surface of a freshly fractured specimen, chain of large elongated crystals (arrow), further chains of smaller crystals and other details in Fig. 1. (B) Energy-dispersive x-ray spectrometry analyses of elemental composition showing position of Fe-rich rim (detailed data are presented in Appendix 2, which is published as supplemental data on the PNAS web site, www.pnas.org). (C) Similar site in a resin-embedded, sectioned, and polished specimen, one chain marked by arrow, also site of Auger electron spectroscopy analyses. (D) Results of analyses of areas outlined in C: squares, magnetite crystal chains present; triangles, absent; ca, carbonate; px, orthopyroxene.

Figure 4

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Quoted from PubMedSource: Proc. Natl. Acad. Sci. USA  vol. 98, no. 5, pp. 2176-2181, February 27, 2001

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