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 Historical Development

Any analysis of the history of magnetofossils must begin with the work of Heinz A. Lowenstam (1962), a Professor at Caltech from 1954 until he passed away in 1994. His seminal discovery of magnetite (Fe3O4) biomineralization in the teeth of chitons (mollusks of the class Polyplacophora) demonstrated that living organisms were able to precipitate the mineral magnetite, despite the widespread impression that it was chemically out of equilibrium in living systems. Lowenstam realized that the teeth of these animals were continuously being worn away at the anterior end and being replaced at the posterior end, so some of the tooth debris must have wound up in marine sediments. However, no one has yet identified a clear magnetofossil from a chiton tooth.

     The next critical discovery was the discovery of the magnetotactic bacteria by Richard Blakemore in 1975. If these had never been noticed (almost by accident), we would never have thought to look for the fossil remains of magnetosomes in marine sediments. Readers interested in these intriguing organisms are referred to the homepage for the magnetotactic bacteria maintained by Richard Frankel.

     The first direct attempt to assess the possibility that biogenic magnetite might be contributing to the remanent paleomagnetism in marine sediments was made by Kirschvink and Lowenstam (1979). Although the title of the paper refers specifically to the magnetite produced by chitons, they have an extensive discussion of the possibility that the magnetotactic bacteria could be generating bacterial magnetofossils. They were also the first to observe that the size and shape of the bacterial crystals reported by Blakemore implied that they were single magnetic domains according to the theoretical calculations by Butler and Banerjee (1975), and they made initial order of magnitude estimates concerning the intensity of remanent magnetism which magnetotactic bacteria might generate in marine sediments.

     As of 1979, however, no sub-micron sized magnetite particles had ever been extracted from marine sediments and actually examined by transmission electron microscopy (TEM) for the presence of crystals which might have looked like those made by the magnetotactic bacteria. Ordinary optical microscopies, and the scanning electron microscopy (SEM) techniques available at the time, were not adequate for doing this. In an important paper, Towe & Moench (1981) used better estimates of the bacterial population densities and generation times to increase the estimates of the potential contribution of bacterial magnetite to the remanent magnetism of sediments. However, Kirschvink and Chang (1984) reported the first clear magnetofossils, using a magnetic extraction technique and weak acetic acid, and studied the extracts with TEM. Although a rather obvious construction, the term, 'magnetofossil', was actually coined in that paper at the suggestion of Stan Awramik (of UCSB).

     The next intriguing discovery was made by Anne Demitrack in 1985, who, for her Masters thesis work at Stanford, studied magnetic extracts from the pond at Woods Hole, MA, where Blakemore had originally discovered the magnetotactic bacteria. Surprisingly, she discovered magnetosome-like objects that were made of the mineral Greigite (Fe3S4). At the time, Greigite precipitating magnetotactic bacteria had not yet been discovered, so she concluded that these were probably originally made of magnetite which might have been altered chemically during burial in the sediment. Now we think that she made the first discovery of Greigite magnetofossils, several years before the first discovery of Greigite based magnetosome in living magnetotactic bacteria (Heywood et al., 1990; Mann et al., 1990).

     The next major discovery was done by Nikolai Petersen, Hojatollah Vali, and Tilo von Dobeneck (1986) in Munich, Germany. They used a gentle extraction technique to remove the magnetic particles in deep sea muds, and found that they could sometimes preserve the chain-like organization of the individual magnetosomes, sometimes even preserving the organic materials surrounding them (remnants of the magnetosome membranes). Hojatollah Vali was particularly instrumental in producing extraordinarily high-resolution TEM images. The presence of clear magnetosome chains was a critical factor in convincing a skeptical rock magnetic and paleomagnetic community that biogenic magnetites were indeed responsible for much of the stable remanent magnetization observed in deep sea sediments. They were even found to be providing a weak but stable magnetization in shallow-water carbonate platforms, an observation which has led to a number of magnetostratigraphic studies providing age constraints on these otherwise-difficult to date strata (McNeill et al., 1988, 1990, 1993; Aissaoui et al., 1990, 1991).

     After these seminal contributions, there was a flurry of observations of bacterial magnetofossils in a variety of marine and terrestrial environments. It soon became clear, however, that magnetofossils per se were almost useless for biostratigraphy. The crystal morphology of bacterial magnetofossils did not change very much with time, although they did seem to have some utility for simply indicating the presence of bacterial activity (more on his later). Most of the literature on magnetofossils was therefore confined to the geophysical journals, and the topic received little attention from paleontologists. Nevetheless, it is now almost routine to search for them in sediments being examined for paleomagnetism; the presence of unaltered magnetosomes is a good indication that original magnetization might be present. Only a few examples have been identified where unusual clay composition is responsible for disrupting the natural magnetization of sediments which contain otherwise pristine magnetofossils (Vali and Kirschvink, 1989). In the late 1980s, the fossil record was extended back about 2 billion years after it was recognized that modern algal mat communities had good populations of magnetotactic bacteria, and some Precambrian stromatolites could be good sources for finding magnetofossils (Chang et al., 1988, Chang and Kirschvink 1989, Stoltz et. al, 1988). Surprisingly, no clear magnetofossils have been discovered from any Earthly sediments older than about two billion years. This might indicate that Earth's Archean and Early Proterozoic environment did not have vertical oxygen gradients like those of the modern Earth, although much more work needs to be done on this problem.

     A rather surprising and more recent observation is that the crystal morphology of the magnetofossils may yield information about relative climatic change. Both Hesse (1994) and Yamazaki and Kawahata (1998) found systematic variations in magnetosome shape that correlated nicely with Pleistocene climatic fluctuations in deep-sea Pacific sediments. These may represent slight differences in the bacterial species composition of the deep-sea benthic environment that fluctuate with time.

     One of the most interesting debates involving magnetofossils concerns their use by McKay et al. (1996) as biomarkers in the ALH84001 Martian meteorite. This is clearly the most interesting and innovative use of potential magnetosomes as a biomarker.

     Natural selection of the magnetic properties of bacterial magnetosomes has left a clear fingerprint of biological activity in the size, shape, crystallinity, and chemistry of bacterial magnetosomes. As shown in the figure here, many bacterial magnetosomes have a set of distinctive features that cannot yet be formed through any known inorganic processes. In fact, there is an entire industry that is devoted to manufacturing fine-grained magnetic particles for use in magnetic recording tapes, computer disk drives, and similar things. This is the Ferrite Industry (worth ~ $ 35 billion per year), and they have tried to make magnetic particles similar to those produced by the magnetotactic bacteria for nearly 50 years through inorganic means, and have failed. As the value of a biomarker is directly proportional to the difficulty of forming it inorganically, a population of elongate magnetofossils with these distinctive features is a strong indication of bacterial activity. The paper by Kathie Thomas-Keptra et al. (2000) actually provides the strongest case yet for the existence of ancient life on Mars, but the debate is sure to continue! However, given the importance of the ferrite industry to modern information technology, anyone who figures out a simple, low-temperature method for generating large numbers of elongate single-domain magnetite crystals, of uniform size and shape, etc., will be so rich they should be able to fund a Mars trip on their own!

 Magnetofossil References in Chronological Order
(If I've missed something, please let me know!)

Lowenstam, H. A. (1962). "Magnetite in denticle capping in recent chitons (Polyplacophora)." Bulletin of the Geological Society of America 73: 435-438.

Blakemore, R. P. (1975). "Magnetotactic bacteria." Science 190: 377-379.

Butler, R. F. and S. K. Banerjee (1975). "Theoretical single-domain size range in magnetite and titanomagnetite." Journal of Geophysical Research 80: 4049-4058.

Kirschvink, J. L. (1979). I. A paleomagnetic approach to the Precambrian-Cambrian boundary problem. II. Biogenic magnetite: its role in the magnetization of sediments and as the basis of magnetic field detection in animals. Division of Geological & Geophysical Sciences. Princeton, N.J., Princeton University.

Kirschvink, J. L. and H. A. Lowenstam (1979). "Mineralization and magnetization of chiton teeth: Paleomagnetic, sedimentologic, and biologic implications of organic magnetite." Earth & Planetary Science Letters 44: 193-204.

Towe, K. and T. Moench (1981). "Electron-Optical Characterization of Bacterial Magnetite." Earth and Planetary Science Letters 52: 213-220.

Kirschvink, J. L. (1983). "Biomagnetic Geomagnetism." Reviews of Geophysics 21(3): 672-675.

Chang, S. R. and J. L. Kirschvink (1984). Bacterial magnetofossils as probes of Precambrian ecological and biochemical evolutionary events. 97th annual meeting, Abstracts with Programs - Geological Society of America.

Kirschvink, J. L. and S.-B. R. Chang (1984). "Ultra fine-grained magnetite in deep-sea sediments: possible bacterial magnetofossils." Geology 12: 559-562.

Chang, S.-B. R. and J. L. Kirschvink (1985). Possible Biogenic Magnetite Fossils from the Miocene Marine Clay of Crete. Magnetite Biomineralization and Magnetoreception in Organisms: A New Biomagnetism. J. L. Kirschvink, D. S. Jones and B. McFadden. New York, N.Y., Plenum Press. 5: 647-669.

Demitrack, A. (1985). A search for bacterial magnetite in the Sediments of eel Marsh, Woods Hole, Massachusetts. Magnetite Biomineralization and Magnetoreception in Organisms: A New Biomagnetism. J. L. Kirschvink, D. S. Jones and B. J. MacFadden. New York, Plenum Press. 5: 625-644.

Petersen, N., T. Von Dobeneck, et al. (1986). "Fossil Bacterial Magnetite in Deep-Sea Sediments from the South-Atlantic Ocean." Nature 320(6063): 611-615.

Stolz, J. F., S.-B. R. Chang, et al. (1986). "Magnetotactic bacteria and single-domain magnetite in hemipelagic sediments." Nature 321: 849-851.

Chang, S.-B. R., J. L. Kirschvink, et al. (1987). "Biogenic magnetite as a primary remanence carrier in limestone." Phys. Earth & Planetary Interiors 46: 289-303.

Vali, H., O. Forster, et al. (1987). "Magnetotactic Bacteria and Their Magnetofossils in Sediments." Earth and Planetary Science Letters 86(2-4): 389-400.

von Dobeneck, T., N. Petersen, et al. (1987). "Bakterielle Magnetofossilien; Palaeomagnetische und palaeontologische Spuren einer ungewoehnlichen Bakteriengruppe. (Bacterial magnetofossils; paleomagnetic and paleontologic traces of an unusual bacterial group)." Geowissenschaften in unserer Zeit 5: 27-35.

Bazylinski, D. A., R. B. Frankel, et al. (1988). "Anaerobic Magnetite Production by a Marine, Magnetotactic Bacterium." Nature 334(6182): 518-519.

McNeill, D. F., R. N. Ginsburg, et al. (1988). "Magnetostratigraphic dating of shallow-water carbonates from San Salvador, the Bahamas." Geology 16: 8-12.

Chang, S.-B. R., S. J.F., et al. (1989). "Biogenic magnetite in stromatolites. II. Occurrence in ancient sedimentary environments." Precambrian Research 43: 305-315.

Chang, S. B. R. and J. L. Kirschvink (1989). "Magnetofossils, the Magnetization of Sediments, and the Evolution of Magnetite Biomineralization." Annual Review of Earth and Planetary Sciences 17: 169-195.

Stolz, J. F., S.-B. R. Chang, et al. (1989). The effect of magnetotactic bacteria on the magnetic properties of marine sediments. Origin, evolution, and modern aspects of biomineralization in plants and animals. R. E. Crick. New York, Plenum press: 497-506.

Stolz, J. F., S.-B. R. Chang, et al. (1989). "Biogenic magnetite in stromatolites. I. Occurrence in modern sedimentary environments." Precambrian Research 43: 295-304.

Vali, H. and J. L. Kirschvink (1989). "Magnetofossil Dissolution in a Paleomagnetically Unstable Deep- Sea Sediment." Nature 339(6221): 203-206.

Vali, H., T. Von Dobeneck, et al. (1989). "Biogenic and Lithogenic Magnetic Minerals in Atlantic and Pacific Deep-Sea Sediments and Their Paleomagnetic Significance." Geologische Rundschau 78(3): 753-764.

Aissaoui, D. M., D. F. McNeill, et al. (1990). "Magnetostratigraphic Dating of Shallow-Water Carbonates from Mururoa Atoll, French-Polynesia - Implications for Global Eustasy." Earth and Planetary Science Letters 97(1-2): 102-112.

Farina, M., D. M. S. Esquivel, et al. (1990). "Magnetic Iron-Sulfur Crystals from a Magnetotactic Microorganism." Nature 343(6255): 256-258.

Fassbinder, J. W. E., H. Stanjek, et al. (1990). "Occurrence of Magnetic Bacteria in Soil." Nature 343(6254): 161-163.

Heywood, B. R., D. A. Bazylinski, et al. (1990). "Controlled biosynthesis of Greigite (Fe3S4) in magnetotactic bacteria." Naturwissenschaften 77(11): 536-538.

Mann, S., N. H. C. Sparks, et al. (1990). "Biomineralization of Ferrimagnetic Greigite (Fe3S4) and Iron Pyrite (FeS2) in a Magnetotactic Bacterium." Nature 343(6255): 258-261.

McNeill, D. F. (1990). "Biogenic Magnetite from Surface Holocene Carbonate Sediments, Great Bahama Bank." Journal of Geophysical Research-Solid Earth and Planets 95(B4): 4363-4371.

Stolz, J. F., D. R. Lovley, et al. (1990). "Biogenic Magnetite and the Magnetization of Sediments." Journal of Geophysical Research-Solid Earth and Planets 95(B4): 4355-4361.

Aissaoui, D. M. and J. L. Kirschvink (1991). "Atoll magnetostratigraphy - calibration of the Eustatic records." Terra Nova 3: 35-40.

Akai, J., T. Sato, et al. (1991). "Tem Study on Biogenic Magnetite in Deep-Sea Sediments from the Japan Sea and the Western Pacific-Ocean." Journal of Electron Microscopy 40(2): 110-117.

Oldfield, F. (1991). "Sediment Magnetism - Soil-Erosion, Bushfires, or Bacteria." Geology 19(12): 1155-1156.

Yamazaki, T., I. Katsura, et al. (1991). "Origin of Stable Remanent Magnetization of Siliceous Sediments in the Central Equatorial Pacific." Earth and Planetary Science Letters 105(1-3): 81-93.

Bloemendal, J., J. W. King, et al. (1992). "Rock Magnetism of Late Neogene and Pleistocene Deep-Sea Sediments - Relationship to Sediment Source, Diagenetic Processes, and Sediment Lithology." Journal of Geophysical Research-Solid Earth 97(B4): 4361-4375.

Diaz-Ricci, J. C. and J. L. Kirschvink (1992). "Magnetic domain state and coercivity predictions for biogenic greigite (Fe3O4): A comparison of theory with magnetosome observations." Journal of Geophysical Research 97: 17309-17315.

Mulsow, S. and D. C. Rhoads (1992). Deposition and accumulation of biogenic magnetite in low oxygen facies. Biomineralization processes of iron and manganese; modern and ancient environments. H. C. W. Skinner and R. W. Fitzpatrick. Cremlingen-Destedt, Federal Republic of Germany (DEU), Catena-Verlag Rohdenburg. 21: 303-319.

McNeill, D. F. and J. L. Kirschvink (1993). "Early dolomitization of platform carbonates and the preservation of magnetic polarity." J. Geophys. Res. 98: 7977-7986.

Moskowitz, B. M., R. B. Frankel, et al. (1993). "Rock Magnetic Criteria for the Detection of Biogenic Magnetite." Earth and Planetary Science Letters 120(3-4): 283-300.

Sato, T., K. Kobayashi, et al. (1993). "Variations in Fe3O4 and CaCO3 Contents in Dee-Sea Cores from the Western Equatorial Pacific." J. Geomag. Geoelectr. 45: 125-132.

Stolz, J. F. (1993). "Magnetosomes." Journal of General Microbiology 139: 1663-1670.

Evans, M. E. and F. Heller (1994). "Magnetic Enhancement and Paleoclimate - Study of a Loess/Palaeosol Couplet across the Loess Plateau of China." Geophysical Journal International 117(1): 257-264.

Hesse, P. P. (1994). "Evidence for Bacterial Paleoecological Origin of Mineral Magnetic Cycles in Oxic and Sub-Oxic Tasman Sea Sediments." Marine Geology 117(1-4): 1-17.

Oldfield, F. (1994). "Toward the Discrimination of Fine-Grained Ferrimagnets by Magnetic Measurements in Lake and near-Shore Marine-Sediments." Journal of Geophysical Research-Solid Earth 99(B5): 9045-9050.

Snowball, I. F. (1994) Bacterial magnetite and the magnetic properties of sediments in a Swedish lake. Earth and Planetary Science Letters 126, 129-142.

Stanjek, H., J. W. E. Fassbinder, et al. (1994). "Evidence of biogenic greigite (ferrimagnetic Fe3O4) in soil." Eur. J. Soil Sci. 45: 97-103.

Verosub, K. L. and A. P. Roberts (1995). "Environmental Magnetism - Past, Present, and Future." Journal of Geophysical Research-Solid Earth 100(B2): 2175-2192.

Hanzlik, M., M. Winklhofer, et al. (1996). "Spatial arrangement of chains of magnetosomes in magnetotactic bacteria." Earth and Planetary Science Letters 145(1-4): 125-134.

McKay, D. S., E. K. Gibson, et al. (1996). "Search for past life on Mars: Possible relic biogenic activity in Martian meteorite ALH84001." Science 273(5277): 924-930.

Jia, R.F., B. Z. Yan, R. S. Li, G. C. Fan, and B. H. Lin. (1996) Characteristics of magnetotactic bacteria in Duanjiapo loess section, Shaanxi Province and their environmental significance. Science in China Series D 39, 478-485.

Peck, J. A. and J. W. King (1996). "Magnetofossils in the sediment of Lake Baikal, Siberia." Earth and Planetary Science Letters 140(1-4): 159-172.

Bazylinski, D. A. and B. M. Moskowitz (1997). Microbial biomineralization of magnetic iron minerals: Microbiology, magnetism and environmental significance. Geomicrobiology: Interactions between Microbes and Minerals. 35: 181-223.

Belkaaloul, N. K. and D. M. Aissaoui (1997). "Nature and origin of magnetic minerals within the Middle Jurassic shallow-water carbonate rocks of the Paris Basin, France: implications for magnetostratigraphic dating." Geophysical Journal International 130(2): 411-421.

Barskov, I. S. and A. Y. Rozanov (1998). "Magnetite biomineralization, magnetofossils, and magnetoreception in organisms." Advanced mineralogy 3: 255-257.

Frankel, R. B., J. P. Zhang, et al. (1998). "Single magnetic domains in magnetotactic bacteria." Journal of Geophysical Research-Solid Earth 103(B12): 30601-30604.

Konhauser, K. O. (1998). "Diversity of bacterial iron mineralization." Earth-Science Reviews 43(3-4): 91-121.

Lean, C.M.B. and I. N. McCave. (1998) Glacial to interglacial mineral magnetism and palaeooceanographic changes at Chatham Rise, SW Pacific Ocean. Earth and Planetary Science Letters 163, 247-260.

Paul Montgomery, Ernie A. Hailwood, Andy S. Gale and Jackie A. Burnett (1998). The magnetostratigraphy of Coniacian-Late Campanian chalk sequences in southern England. Earth and Planetary Science Letters 156, 209-224.

Thomas-Keptra, K. L., D. A. Bazylinski, et al. (1998). Evidence for Martian biogenic activity? Elongated prismatic magnetite crystals in ALH84001 carbonate globules. GSA annual meeting, Toronto, Canada, Geological Society of America.

Yamazaki, T. and H. Kawahata (1998). "Organic carbon flux controls the morphology of Magnetofossils in marine sediments." Geology 16(12): 1064-1066.

Zhang, C. L., H. Vali, et al. (1998). "Formation of single-domain magnetite by a thermophilic bacterium." American Mineralogist 83(11-12): 1409-1418.

Gibbs-Eggar, Z., B. Jude, et al. (1999). "Possible evidence for dissimilatory bacterial magnetite dominating the magnetic properties of recent lake sediments." Earth and Planetary Science Letters 168(1-2): 1-6.

Kirschvink, J. L. and H. Vali (1999). Criteria for the identification of bacterial magnetofossils on Earth or Mars. California paleontology conference, abstracts, Pasadena, CA, SourcePaleoBios.

Mandernack, K. W., D. A. Bazylinski, et al. (1999). "Oxygen and iron isotope studies of magnetite produced by magnetotactic bacteria." Science 285(5435): 1892-1896.

Oldfield, F., P. G. Appleby, et al. (1999). "Problems of core correlation, sediment source ascription and yield estimation in Ponsonby Tarn, West Cumbria, UK." Earth Surface Processes and Landforms 24(11): 975-992.

Oldfield, F. and R. J. Wu (2000). "The magnetic properties of the recent sediments of Brothers Water, NW England." Journal of Paleolimnology 23(2): 165-174.

Snowball, I., P. Sandgren and G. Petterson (1999). The mineral magnetic properties of an annually laminated Holocene lake-sediment sequence in northern Sweden. The Holocene 9, 353-362.

Peng, X., R. Jia, R. Li, S. Dai, and T. S. Liu. (2000) Paleo-environmental study on the growth of magnetotactic bacteria and the precipitation of magnetosomes in Chinese loess-paleosol sequences. Chinese Science Bulletin 45, 21-25.

Thomas-Keptra, K. L., D. A. Bazylinski, et al. (2000). "Elongated Prismatic Magnetite Crystals in ALH84001 Carbonate Globules: Potential Martian Magnetofossils." Geochimica Cosmochimica Acta 64 (23), 4049-4081.

Thomas-Keptra, K. L. , Clemett, S.J., Bazylinski, D.A., Kirschvink, J.L., McKay, D.S., Wentworth S.J., Vali, H., Gibson, E.K. Jr., McKay, M.F., and Romanek, C.S.(2001) Truncated hexa-octahedral magnetite crystals in ALH84001: Presumptive biosignatures. Proceedings of the National Academy of Sciences (USA), 98 (5): 2164-2169.

Mihaly Pssfai, Krisztina Cziner, Emv Marton, Piter Marton, Peter R. Buseck, Richard R B. Frankel, Dennis A. Bazylinski (2001). Crystal-size distributions and possible biogenic origin of Fe sulfides. European Journal of Mineralogy 13 (4): 691-703.

Oyvind Paasche, Reidar Lovliea, Svein Olaf Dahl, Jostein Bakkeb, Atle Nesjea. (2004) Bacterial magnetite in lake sediments: late glacial to Holocene climate and sedimentary changes in northern Norway. Earth and Planetary Science Letters 223, 319-333.

Weiss, B.P., Kim,S., Kirschvink, J.L., Kopp, R.E., Sankaran M., Kobayashi, A., & Komeili, A. (2004) Ferromagnetic resonance and low temperature magnetic tests for biogenic magnetite, Earth & Planetary Science Letters 224, 73-89.

Weiss, B.P., Kim, S., Kirschvink, J.L., Kopp, R.E., Sankaran, M. Kobayashi A. & Komelil A. (2004) Magnetic tests for magnetosome chains in Martian meteorite ALH84001. Proc. Nati. Acad. Sci. 101, 8281-8284.

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