Geobiomagnetism

Geobiomagnetism refers to the interaction of living organisms with the earth's magnetic field. Many animals, plants, and even bacteria have displayed in laboratory experiments the ability to sense and to use the earth's magnetic field in various ways, notably in navigation.

The ability of living organisms to navigate accurately over great distances has long fascinated and baffled naturalists and life scientists. How are many species of birds able to migrate thousands of miles annually, often across open seas, and unerringly reach their destinations? How can homing pigeons find their way back to their coops after having been taken many miles from them in enclosed containers? How can honeybees, after having located a desirable food source miles away from their hives, not only return to the food source but also communicate its location to other honeybees? These are only three examples of the remarkable navigation abilities displayed by a variety of living organisms. Systematic research into methods by which animals navigate began in the late 1930s. In experiments in the 1940s and 1950s, researchers showed that living organisms use a variety of means to find directions. These means include celestial navigation (use of the sun and the stars to find directions), which is used by several species of migratory birds and some crustaceans, and navigation by sound reflection, which is used by bats and many forms of sea-dwelling mammals. Other methods include navigation by electricity, used by many species of fish, and navigation by using the earth's magnetic field. Life-forms as diverse as bacteria, butterflies, fish, and birds have built-in compasses, in the form of minute, magnetic, mineral grains, that enable them to orient to the earth's magnetic field.

Birds' Use of EMF

German researcher Hans Fromme was conducting observations of several robins in a cage at the Frankfurt Zoological Institute in 1957 at a time that they were preparing for their annual migration to Spain. Fromme was not satisfied with the then-accepted theory that the robins found their way to Spain by celestial navigation, because radar data of the birds had shown that they flew straight toward their destination even when heavy cloud cover hindered the visibility of the sky. Fromme caged his birds in a windowless room. Nevertheless, when the robins outside began their southwestward migration, Fromme's birds became restless and fluttered up to the southwestern corner of their cage. Fromme reasoned that they were responding to some stimulus other than the stars or the sun. He guessed that this stimulus might be the earth's magnetic field. Scientists had long known that the earth acts in many ways as a giant electromagnet of considerable power. Until Fromme's experiments, however, few scientists suspected that geomagnetism affected living organisms or could be used by them for various purposes.

To test his theory, Fromme put his birds into a special steel chamber that reduced the power of the earth's magnetic field (EMF) to 0.14 gauss (a unit of measure for magnetic force). The average strength of the EMF at Frankfurt is 0.41 gauss. In this enclosure, the robins still became restless at their normal migration time, but their flutterings were random, no longer toward the southwest corner of the cage. Further research showed that over a period of days the robins adjusted to the reduced magnetic field and once again flew toward the southwest corner of their cage. Fromme and his colleagues were able to “fool” the robins by creating an artificial magnetic field that created a false southwest. The robins rapidly adjusted to the artificial field and fluttered toward the southwest of the artificial field.

After Fromme's experiments proved that robins used the EMF to navigate, life scientists began investigating the effects of geomagnetism on a variety of life-forms, ranging from bacteria to higher vertebrates, including human beings. These experiments resulted in a series of dramatic and unexpected discoveries.

In addition to Fromme's experiments with robins, other experiments have demonstrated conclusively that many species of birds rely on the EMF to navigate. The homing pigeon provides perhaps the best example. Carefully conducted experiments showed that a simple bar magnet attached to the back of a homing pigeon's head completely disrupts its navigational ability. Other experiments showed that homing pigeons are remarkably sensitive to minute local fluctuations (anomalies) in the EMF, which may perhaps explain their remarkable homing ability.

Other Organisms' Use of EMF

One group of scientists observed anaerobic bacteria of the Spirillum type, which are usually found in aquatic mud. When taken into open water, the bacteria swim along magnetic field lines, natural or artificial, which take them toward the magnetic north pole in the Northern Hemisphere and the magnetic south pole in the Southern Hemisphere. This reaction takes them directly to their natural habitat, the mud of the sea floor.

Other scientists have shown that different species of insects use the EMF in a number of ways and for a variety of purposes. The common honeybee, for example, can communicate the location of a food source to its hive mates by use of the EMF, without the hive mates having visited the site. The honeybee accomplishes this by performing a complicated series of movements (called a “waggle dance”) on the honeycomb in which its movements are oriented by the EMF. The so-called compass termite of Australia uses the EMF in an entirely different way from the honeybee. Compass termites build large nests, sometimes 13 feet high and 10 feet long but only about 3 feet wide, the temperature of which is regulated by use of the EMF. The long axis of the nest always runs due north and south. This magnetic orientation has the advantage of exposing the long sides of the nest to the direct warming rays of the sun during the early morning and late afternoon. In the middle of the day, when the sun's rays might be too hot, however, only the relatively thin top edge is exposed to its direct rays.

Many species of fish also use the EMF. Sharks and rays, for example, are apparently able to detect changes in the EMF to locate potential prey. Scientists have shown that the fish interact with the EMF by introducing electrical fields into their environment, which they use to orient themselves in the EMF and to register fluctuations therein caused by magnetic anomalies or by other living creatures. The organ involved in the fish's ability to interact with the EMF appears to be the electroreceptive ampullae of Lorenzini, which respond to very low electrical voltage gradients. Freshwater eels, both the European and the American varieties, apparently use the EMF to guide them from the rivers where they spend their adolescence to the Sargasso Sea, to which they migrate for purposes of reproduction once they have reached maturity.

Magnetic Properties of Higher Organisms

Scientists investigating the magnetic properties of higher organisms have also made spectacular and unexpected discoveries. Researchers in this area, called biomagnetism, have found that most organs in higher vertebrates (including humans) produce weak magnetic fields that can be detected and measured using the very sensitive instruments. The organs producing such magnetic fields include the liver, the brain, and the heart. Magnetic measurements of these organs provide information about them that no other sort of test, including X-rays and electroencephalograms, can yield. A number of researchers in the field of biomagnetism suspect that the magnetic fields produced by some living organisms allow them somehow to use the EMF for direction-finding. This relationship, however, has not yet been scientifically demonstrated.

Instruments for Studying Geobiomagnetism

The sensitive instruments necessary to study geobiomagnetism emerged from weapons research conducted during World War II. In their efforts to discover ever more efficient ways to detect enemy submarines and aircraft, scientists in both Allied and Axis countries investigated various applications of electromagnetism. Governments invested huge sums of money into scientific research projects that offered even a tenuous hope of producing revolutionary weapons. Some of the better-known results of these military-oriented scientific projects include radar, sonar, and nuclear fission. After the war, a part of the research conducted by military research projects led to the development of instruments capable of detecting the very weak magnetic fields produced by living organisms, or biomagnetism.

Biomagnetic fields are very faint, usually less than one-tenth that of the earth, and cannot be measured with the magnometers used to measure the EMF. Magnetic fields stronger than 1 gauss are measurable by a simple but sensitive magnetometer called a fluxgate. Measurement of weaker fields requires the use of an extremely sensitive cryogenic magnetometer called a SQUID (acronym for superconducting quantum interference device). No instrument yet devised, however, has been able to show how organisms interact with the EMF or which device or organ is involved in that interaction, although some clues have been discovered. Nevertheless, abundant evidence exists that such interaction does take place.

In the experiments with bacteria mentioned earlier, researchers introduced an artificial magnetic field pointing at right angles to the sea bottom. The bacteria invariably aligned themselves with the new field. When scientists cultured these bacteria in a largely iron-free medium, the bacteria lost their ability to orient themselves along the EMF. Upon examination, the researchers found the bacteria that were cultured in a natural environment contained 1.5 percent (dry weight) iron, which almost certainly is the agent that allows their interaction with the EMF. Exactly how this interaction occurs, however, is unknown.

Theories of Geobiomagnetism

Geophysicists have proposed several theories about which mechanisms are at work in geobiomagnetism. The paramagnetic molecule theory states that molecules with unpaired magnetic spins are present in all living cells, which may line up with external magnetic fields, although this has yet to be demonstrated. Even if such alignment does occur, there is no evidence or even theory as to how an organism's nervous system could use the information to deduce the direction of the field. The electrodynamic theory states that if a force of electrically charged particles is introduced into a magnetic field, the field exerts a force that influences their direction of motion. Whether detectable effects can be produced in living organisms, allowing them to detect the weak EMF, continues to be debated and has yet to be demonstrated. According to the magnet hypothesis, the ingestion of magnetic material or the formation of magnetic material within specialized cells by living organisms allows them to sense the earth's magnetic field. Magnetotactic bacteria produce intercellular iron sulfide, greigite, which is magnetic. Magnetite, an iron oxide, in the trigeminal nerve cells of trout and other fish enables them to detect changes in the magnetic field. German scientist Dominik Heyers published evidence in 2007 that migratory birds use a visual link to the brain, allowing them to “see” magnetic fields. By 2021, further research had been conducted by a collaboration of biologists, chemists, and physicists at the University of Oxford and the University of Oldenburg. These researchers analyzed the magnetic sense of birds, such as the European robin, that migrate at night. They concluded that these birds receive their magnetic sense from a light-sensitive protein, cryptochrome 4, that is found in the retinas in their eyes.

Applications Benefiting Humankind

Learning the methods by which living organisms sense and use the EMF for navigation could be beneficial. In theory, the EMF could be used to steer planes and ships to their destinations, forgoing the need for expensive and complicated navigational equipment.

The new field of biomagnetism has already yielded unexpected results in medical technology. It is not inconceivable that, as we learn more about the magnetic properties of living organisms and their interaction with the EMF, ways of treating malfunctions of bodily processes through manipulating these magnetic fields will evolve.

Principal Terms

biomagnetism: the magnetic fields generated by living organisms

geomagnetism: the magnetic field generated by the earth

magnetite: an isometric mineral, an oxide that is sensitive to magnetic fields

magnetometer: a device used to detect and measure magnetic fields

SQUID: an extremely sensitive magnetometer capable of detecting and measuring very weak magnetic fields

Bibliography

Barnothy, Madeleine F., ed. Biological Effects of Magnetic Fields. 2 vols. New York: Plenum Press, 1964, 1969.

Blakemore, R. P., and R. B. Frankel. “Magnetic Navigation in Bacteria.” Scientific American 245 (June 1981): 42-49.

Dubrov, A. P. The Geomagnetic Field and Life. New York: Plenum Press, 1978.

Fenwick, Peter. “The Inverse Problem: A Medical Perspective.” Physics in Medicine and Biology 32 (April 1987): 5-10.

Gulrajani, Ramesh M. Bioelectricity and Biomagnetism. New York: Wiley, 1998.

Hamblin, William K., and Eric H. Christiansen. Earth's Dynamic Systems. 10th ed. Upper Saddle River, N.J.: Prentice Hall, 2003.

Ioannides, A. A. “Trends in Computational Tools for Biomagnetism: From Procedural Codes to Intelligent Scientific Models.” Physics in Medicine and Biology 32 (January 1987): 77-84.

Jungreis, Susan A. “Biomagnetism: An Orientation Mechanism in Migrating Insects?” Florida Entomologist 70 (1987): 277-283.

Kholodov, E. A. Magnetic Fields of Biological Objects. Translated by A. N. Taruts. Moscow: Nauka, 1990.

Malmivuo, Jaakko. Bioelectromagnetism: Principles and Applications of Bioelectric and Biomagnetic Fields. New York: Oxford University Press, 1995.

Markl, Hubert. “Geobiophysics: The Effect of Ambient Pressure, Gravity and of the Geomagnetic Field on Organisms.” Translated by B. P. Winnewisser in Biophysics, edited by Walte Hoppe et al. New York: Springer-Verlag, 1983.

Plummer, Charles C., and Diane Carlson. Physical Geology. 12th ed. Boston: McGraw-Hill, 2007.

Reite, M., and J. Zimmerman. “Magnetic Phenomena of the Central Nervous System.” Annual Review of Biophysics and Bioengineering 7 (1978): 167-188.

Reppert, Steven M., Robert J. Gegear, and Christine Merlin. “Navigational Mechanisms of Migrating Monarch Butterflies.” Trends in Neurosciences, 33 (2010): 399-406.

"Solving the Mystery of One, then Two, Dead Magnets at Fermilab." Magnetic Magazine, 15 Apr. 2024,

magneticsmag.com/solving-the-mystery-of-one-then-two-dead-magnets-at-fermilab/. Accessed 9 Feb. 2025.

Street, Philip. Animal Migration and Navigation. New York: Charles Scribner's Sons, 1976.

Timmel, Christiane, Peter Hore, and Stuart Mackenzie. "How Birds Sense the Magnetic Field of Earth to Help Them Navigate." Oxford News, 24 June 2021, www.ox.ac.uk/news/science-blog/how-birds-sense-magnetic-field-earth-help-them-navigate. Accessed 9 Feb. 2025.

Walker, Michael M., et al. “Structure and Function of the Vertebrate Magnetic Sense.” Nature 390 (November 1997): 371-376.

Wiltschko, Wolfgang, and Roswitha Wiltschko. “Magnetic Orientation and Magnetoreception in Birds and Other Animals.” Journal of Comparative Physiology. 191 (2008): 675-693.