Magnetofossil

Last updated

Magnetofossils are the fossil remains of magnetic particles produced by magnetotactic bacteria (magnetobacteria) and preserved in the geologic record. The oldest definitive magnetofossils formed of the mineral magnetite come from the Cretaceous chalk beds of southern England, while magnetofossil reports, not considered to be robust, extend on Earth to the 1.9-billion-year-old Gunflint Chert; they may include the four-billion-year-old Martian meteorite ALH84001.

Contents

Magnetotactic organisms are prokaryotic, with only one example of giant-magnetofossils, likely produced by eukaryotic organisms, having been reported. [1] Magnetotactic bacteria, the source of the magnetofossils, are magnetite (Fe3O4) or greigite (Fe3S4) producing bacteria found in both freshwater and marine environments. These magnetite bearing magnetotatic bacteria are found in the oxic-anoxic transition zone where conditions are such that oxygen levels are less than those found in the atmosphere (microaerophilic). [2] Compared to the magnetite producing magnetotactic bacteria and subsequent magnetofossils, little is known about the environments in which greigite magnetofossils are created and the magnetic properties of the preserved greigite particles.

Existence of magnetotactic bacteria was first suggested in the 1960s, when Salvatore Bellini of the University of Pavia discovered bacteria in a bog that appeared to align themselves with the magnetic field lines of the Earth. [3] Following this discovery researchers began to think of the effect of magnetotactic bacteria on the fossil record and magnetization of sedimentary layers.

Most of the research concentrated on marine environments, [4] although it has been suggested that these magnetofossils can be found in terrestrial sediments (derived from terrestrial sources). [5] These magnetofossils can be found throughout the sedimentary record, and therefore are influenced by deposition rate. Episodes of high sedimentation, not correlating with an increase in magnetobacterial and thus magnetofossil production, can decrease magnetofossil concentrations vastly, although this is not always the case. An increase in sedimentation normally coincides with an increase of land erosion, and therefore an increase in iron abundance and nutrient supply.

Magnetization

Within the magnetotactic bacteria, magnetite and greigite crystals are biosynthesized (biomineralized) within organelles called magnetosomes. These magnetosomes form chains within the bacterial cell and in doing so, provide the organism with a permanent magnetic dipole. The organism uses it for geomagnetic navigation, to align itself with the Earth's geomagnetic field (magnetotaxis) and to reach the optimal position along vertical chemical gradients.

When an organism dies the magnetosomes become trapped in sediments. Under the right conditions, primarily if the redox conditions are correct, the magnetite can then be fossilized and therefore stored in the sedimentary record. [5] The fossilization of the magnetite (magnetofossils) within sediments contributes largely to the natural remanent magnetization of the sediment layers. The natural remanent magnetization is the permanent magnetism remaining in a rock or sediment after it has formed.

Paleoindicators

Magnetotactic bacteria use iron to create magnetite in magnetosomes. As a result of this process, increased iron levels correlate with increased production of magnetotactic bacteria. Increases in iron levels have been long associated with hyperthermal [6] (period of warming, usually between 4-8 degrees Celsius) periods in the Earth's history. These hyperthermal events, such as the Palaeocene-Eocene Thermal Maximum or the Holocene Warm Period (HWP), stimulated increased productivity in planktonic and benthic foraminifera, [6] which in turn, resulted in higher levels of sedimentation. Furthermore, an increase in temperature (like the one in the HWP) may also be associated with a wet period. These warm and wet conditions were favourable for magnetofossil production due to an increased nutrient supply in a period of post-glacial warming during the HWP. As a result, this period shows an increase in magnetofossil concentration. Using this increase in concentration, researchers can use magnetofossils as an indicator of a period of relatively high (or low) temperatures in Earth's history. Dating of these rocks can provide information about the time period of this climate change and can be correlated to other rock formations or depositional environments in which the Earth's climate at that time may not have been as clear. Sediment aging and dissolution or alteration of magnetite present problems with providing useful measurements as the crystals structural integrity may not be preserved. [2]

Magnetofossils are not only being studied for their paleoenvironmental or paleoclimatic indicators. As mentioned above, magnetofossils hold a remanent magnetization when they are formed. That is, the magnetite (or greigite) aligns in the direction of the geomagnetic field. The magnetite crystals can be thought of as being a simple magnet with a north and south pole, this north–south orientation aligns with the north–south magnetic poles of the Earth. These fossils are then buried within the rock record. Researchers can examine these rock samples in a remanent magnetometer where the effects of Earth's current magnetic field is removed, to determine the remanent, or initial, magnetization of the rock sample when it was formed. In knowing the orientation of the rock in-situ and the remanent magnetization, researchers can determine the Earth's geomagnetic field at the time the rock was formed. This can be used as an indicator of magnetic field direction, or reversals in the Earth's magnetic field, where the Earth's north and south magnetic poles switch (which happen on average every 450,000 years).

Research

There are many methods for detecting and measuring magnetofossils, although there are some issues with the identification. Current research is suggesting that the trace elements found in the magnetite crystals [2] formed in magnetotactic bacteria differ from crystals formed by other methods. It has also been suggested that calcium and strontium incorporation can be used to identify magnetite inferred from magnetotactic bacteria. Other methods such as transmission electron microscopy (TEM) [7] of samples from deep boreholes and ferromagnetic resonance (FMR) [8] spectroscopy are being used. FMR spectroscopy of chains of cultured magnetotactic bacteria compared to sediment samples are being used to infer magnetofossil preservation over geological time frames. Research suggests that magnetofossils retain their remanent magnetization at deeper burial depths, although this is not entirely confirmed. FMR measurements of saturation isothermal remanent magnetization (SIRM) in some samples, compared with FMR and rainfall measurements taken over the past 70 years, have shown that magnetofossils can retain a record of paleorainfall variations [9] on a shorter time-scale (hundreds of years), making a very useful recent history paleoclimate indicator. [5]

Summary

The process of magnetite and greigite formation from magnetotactic bacteria and the formation of magnetofossils are well understood, although the more specific relationships, like those between the morphology of these fossils and the effect on the climate, nutrient availability and environmental availability would require more research. This however, does not alter the promise of better insight into the Earth's microbial ecology [9] and geomagnetic variations over a large time scale presented by magnetofossils. Unlike some other methods used to provide information of the Earth's history, magnetofossils normally have to be seen in large abundances to provide useful information of Earth's ancient history. Although lower concentrations can tell their own story of the more recent paleoclimate, paleoenvironmental and paleoecological history of the Earth.

Related Research Articles

<span class="mw-page-title-main">Magnetite</span> Iron ore mineral

Magnetite is a mineral and one of the main iron ores, with the chemical formula Fe2+Fe3+2O4. It is one of the oxides of iron, and is ferrimagnetic; it is attracted to a magnet and can be magnetized to become a permanent magnet itself. With the exception of extremely rare native iron deposits, it is the most magnetic of all the naturally occurring minerals on Earth. Naturally magnetized pieces of magnetite, called lodestone, will attract small pieces of iron, which is how ancient peoples first discovered the property of magnetism.

<span class="mw-page-title-main">Paleomagnetism</span> Study of Earths magnetic field in past

Paleomagnetism is the study of magnetic fields recorded in rocks, sediment, or archeological materials. Geophysicists who specialize in paleomagnetism are called paleomagnetists.

<span class="mw-page-title-main">Rio Tinto (river)</span> River in Spain

The Río Tinto is a river in southwestern Spain that rises in the Sierra Morena mountains of Andalusia. It flows generally south-southwest, reaching the Gulf of Cádiz at Huelva. The Rio Tinto river has a unique red and orange colour derived from its chemical makeup that is extremely acidic and with very high levels of iron and heavy metals.

<span class="mw-page-title-main">Rock magnetism</span> The study of magnetism in rocks

Rock magnetism is the study of the magnetic properties of rocks, sediments and soils. The field arose out of the need in paleomagnetism to understand how rocks record the Earth's magnetic field. This remanence is carried by minerals, particularly certain strongly magnetic minerals like magnetite. An understanding of remanence helps paleomagnetists to develop methods for measuring the ancient magnetic field and correct for effects like sediment compaction and metamorphism. Rock magnetic methods are used to get a more detailed picture of the source of the distinctive striped pattern in marine magnetic anomalies that provides important information on plate tectonics. They are also used to interpret terrestrial magnetic anomalies in magnetic surveys as well as the strong crustal magnetism on Mars.

<span class="mw-page-title-main">Magnetosome</span> Organelle in magnetotactic bacteria

Magnetosomes are membranous structures present in magnetotactic bacteria (MTB). They contain iron-rich magnetic particles that are enclosed within a lipid bilayer membrane. Each magnetosome can often contain 15 to 20 magnetite crystals that form a chain which acts like a compass needle to orient magnetotactic bacteria in geomagnetic fields, thereby simplifying their search for their preferred microaerophilic environments. Recent research has shown that magnetosomes are invaginations of the inner membrane and not freestanding vesicles. Magnetite-bearing magnetosomes have also been found in eukaryotic magnetotactic algae, with each cell containing several thousand crystals.

A geomagnetic excursion, like a geomagnetic reversal, is a significant change in the Earth's magnetic field. Unlike reversals, an excursion is not a "permanent" re-orientation of the large-scale field, but rather represents a dramatic, typically a (geologically) short-lived change in field intensity, with a variation in pole orientation of up to 45° from the previous position.

Magnetotaxis is a process implemented by a diverse group of Gram-negative bacteria that involves orienting and coordinating movement in response to Earth's magnetic field. This process is mainly carried out by microaerophilic and anaerobic bacteria found in aquatic environments such as salt marshes, seawater, and freshwater lakes. By sensing the magnetic field, the bacteria are able to orient themselves towards environments with more favorable oxygen concentrations. This orientation towards more favorable oxygen concentrations allows the bacteria to reach these environments faster as opposed to random movement through Brownian motion.

Magnetospirillum is a Gram-negative, microaerophilic genus of magnetotactic bacteria, first isolated from pond water by the microbiologist R. P. Blakemore in 1975. They have a spiral (helical) shape and are propelled by a polar flagellum at each end of their cells. The three main species identified are M. magnetotacticum strain MS-1, M. griphiswaldense strain MSR-1, and M. magneticum strain AMB-1.

<span class="mw-page-title-main">Magnetotactic bacteria</span> Polyphyletic group of bacteria

Magnetotactic bacteria are a polyphyletic group of bacteria that orient themselves along the magnetic field lines of Earth's magnetic field. Discovered in 1963 by Salvatore Bellini and rediscovered in 1975 by Richard Blakemore, this alignment is believed to aid these organisms in reaching regions of optimal oxygen concentration. To perform this task, these bacteria have organelles called magnetosomes that contain magnetic crystals. The biological phenomenon of microorganisms tending to move in response to the environment's magnetic characteristics is known as magnetotaxis. However, this term is misleading in that every other application of the term taxis involves a stimulus-response mechanism. In contrast to the magnetoreception of animals, the bacteria contain fixed magnets that force the bacteria into alignment—even dead cells are dragged into alignment, just like a compass needle.

Natural remanent magnetization (NRM) is the permanent magnetism of a rock or sediment. This preserves a record of the Earth's magnetic field at the time the mineral was laid down as sediment or crystallized in magma and also the tectonic movement of the rock over millions of years from its original position. Natural remanent magnetization forms the basis of paleomagnetism and magnetostratigraphy.

<span class="mw-page-title-main">Vine–Matthews–Morley hypothesis</span> First key scientific test of the seafloor spreading theory of continental drift and plate tectonics

The Vine–Matthews–Morley hypothesis, also known as the Morley–Vine–Matthews hypothesis, was the first key scientific test of the seafloor spreading theory of continental drift and plate tectonics. Its key impact was that it allowed the rates of plate motions at mid-ocean ridges to be computed. It states that the Earth's oceanic crust acts as a recorder of reversals in the geomagnetic field direction as seafloor spreading takes place.

Magnetostratigraphy is a geophysical correlation technique used to date sedimentary and volcanic sequences. The method works by collecting oriented samples at measured intervals throughout the section. The samples are analyzed to determine their characteristic remanent magnetization (ChRM), that is, the polarity of Earth's magnetic field at the time a stratum was deposited. This is possible because volcanic flows acquire a thermoremanent magnetization and sediments acquire a depositional remanent magnetization, both of which reflect the direction of the Earth's field at the time of formation. This technique is typically used to date sequences that generally lack fossils or interbedded igneous rock. It is particularly useful in high-resolution correlation of deep marine stratigraphy where it allowed the validation of the Vine–Matthews–Morley hypothesis related to the theory of plate tectonics.

Plate reconstruction is the process of reconstructing the positions of tectonic plates relative to each other or to other reference frames, such as the Earth's magnetic field or groups of hotspots, in the geological past. This helps determine the shape and make-up of ancient supercontinents and provides a basis for paleogeographic reconstructions.

Environmental magnetism is the study of magnetism as it relates to the effects of climate, sediment transport, pollution and other environmental influences on magnetic minerals. It makes use of techniques from rock magnetism and magnetic mineralogy. The magnetic properties of minerals are used as proxies for environmental change in applications such as paleoclimate, paleoceanography, studies of the provenance of sediments, pollution and archeology. The main advantages of using magnetic measurements are that magnetic minerals are almost ubiquitous and magnetic measurements are quick and non-invasive.

Iron(II,III) sulfide is a blue-black (sometimes pinkish) chemical compound of iron and sulfur with formula Fe3S4 or FeS·Fe2S3, which is much similar to iron(II,III) oxide. It occurs naturally as the sulfide mineral greigite and is magnetic. It is a bio-mineral produced by and found in magnetotactic bacteria. It is a mixed valence compound, featuring both Fe2+ and Fe3+ centers, in 1:2 ratio.

<span class="mw-page-title-main">Outline of geophysics</span> Topics in the physics of the Earth and its vicinity

The following outline is provided as an overview of and topical guide to geophysics:

Desulfovibrio magneticus is a bacterium. It is sulfate-reducing and is notable for producing intracellular single-domain-sized magnetite particles, making it magnetotactic. Its type strain is RS-1T.

Magnetobacterium bavaricum is a species of bacterium.

<span class="mw-page-title-main">Magnetic field of Mars</span>

The magnetic field of Mars is the magnetic field generated from Mars' interior. Today, Mars does not have a global magnetic field. However, Mars did power an early dynamo that produced a strong magnetic field 4 billion years ago, comparable to Earth's present surface field. After the early dynamo ceased, a weak late dynamo was reactivated ~3.8 billion years ago. The distribution of Martian crustal magnetism is similar to the Martian dichotomy. Whereas the Martian northern lowlands are largely unmagnetized, the southern hemisphere possesses strong remanent magnetization, showing alternating stripes. Our understanding of the evolution of the magnetic field of Mars is based on the combination of satellite measurements and Martian ground-based magnetic data.

Subir Kumar Banerjee is an Indian-American geophysicist, known for research on rock magnetism, palaeomagnetism, and environmental magnetism.

References

  1. ↑ Chang, L.; A.P. Roberts; W. Williams; J.D. Fitz Gerald; J.C. Larrasoana; L. Jovane; A.R. Muxworthy (2012). "Giant Magnetofossils and hyperthermal events". Earth and Planetary Science Letters. 351–352: 258–269. Bibcode:2012E&PSL.351..258C. doi:10.1016/j.epsl.2012.07.031. hdl: 20.500.12468/673 .
  2. 1 2 3 Amor, M.; V. Busigny; M. Durand-Dublef; M. Tharaud; G. Ona-Nguema; A. Gelabert; E. Alphandery; N. Menguy; M.F. Benedetti; I. Chebbi; F. Guyot (2014). "Chemical signature of magnetotactic bacteria". Proceedings of the National Academy of Sciences. 112 (6): 1699–1703. Bibcode:2015PNAS..112.1699A. doi: 10.1073/pnas.1414112112 . PMC   4330721 . PMID   25624469.
  3. ↑ Bellini, Salvatore (1963). "Su di un particolare comportamento di batteri d'acqua dolce" (PDF). California Polytechnic State University. Archived from the original (PDF) on 2010-05-27.
  4. ↑ Heslop, D.; A.P. Roberts; L. Chang; M. Davies; A. Abrajevitch; P. De Decker (2013). "Quantifying magnetite magnetofossil contributions to sedimentary magnetizations". Earth and Planetary Science Letters. 382: 58–65. Bibcode:2013E&PSL.382...58H. doi:10.1016/j.epsl.2013.09.011.
  5. 1 2 3 Reinholdsson, M.; I. Snowball; L. Zillen; C. Lenz; D.J. Conley (2013). "Magnetic enhancement of Baltic Sea sapropels by greigite magnetofossils". Earth and Planetary Science Letters. 366: 137–150. Bibcode:2013E&PSL.366..137R. doi: 10.1016/j.epsl.2013.01.029 .
  6. 1 2 Savian, J.F.; L. Jovane; F. Fabrizio; R.I.F. Trindade; R. Coccioni; S.M. Bohaty; P.A. Wilson; F. Florindo; A.P. Roberts; R. Catanzariti; F. Iacoviello (2013). "Enhanced primary productivity and magnetotactic bacterial production in response to middle Eocene warming in the Neo-Tethys Ocean". Palaeogeography, Palaeoclimatology, Palaeoecology. 414: 32–45. doi:10.1016/j.palaeo.2014.08.009.
  7. ↑ Liu, S.; C. Deng; J. Xiao; J. Li; G.A. Paterson; L. Chang; L. Yi; H. Qin; Y. Pan; R. Zhu (2015). "Insolation driven biomagnetic response to the Holocene Warm Period in semi-arid East Asia". Scientific Reports. 5 (8001): 8001. Bibcode:2015NatSR...5E8001L. doi:10.1038/srep08001. PMC   4303925 . PMID   25614046.
  8. ↑ Gehring, A.U.; J. Kind; M. Charilaou; I. Garcia-Rubio (2012). "S-band ferromagnetic resonance spectroscopy and the detection of magnetofossils". Journal of the Royal Society Interface. 10 (20120790): GP41A–1101. Bibcode:2012AGUFMGP41A1101G. doi:10.1098/rsif.2012.0790. PMC   3565730 . PMID   23269847.
  9. 1 2 Gehring, A.U.; J. Kind; M. Charilaou; I. Garcia-Rubio (2011). "The detection of magnetotactic bacteria and magnetofossils by means of magnetic anisotropy". Earth and Planetary Science Letters. 309 (1–2): 113–117. Bibcode:2011E&PSL.309..113G. doi:10.1016/j.epsl.2011.06.024.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.