Geomagnetic Reversals and Genome Imprinting

ELECTRO- AND MAGNETOBIOLOGY, 16(3), 309-320 (1997)

GEOMAGNETIC REVERSALS AND GENOME IMPRINTING

A. R. Liboff Department of Physics

Oakland University Rochester, Michigan

Key words. clotron resonance

Geomagnetic reversals; Genome imprinting; Avian compass; Ion cy-

ABSTRACT

If it is more fundamental to formulate biological expression in terms of electromagnetic fields, does this also imply that living things are especially sensitive to the external electromagnetic environment? Specifically, we examine possible genomic effects due to reversals of the geomagnetic field. To maintain sensitivity following a reversal, the Wiltschko hypothesis for the avian magnetic compass can be subsumed under an N-B imprinting paradigm, where N is the horizontal vector pointing to magnetic north and B the geomagnetic field vector. Even with a compass that is invariant under reversals, there are nevertheless potential difficulties due to discontinuities in the magnitude of the field during the transition between one chron and the next. Indeed, transitions may be one reason for other-than-magnetic avian auxiliay compasses. Additional problems may also arise during transitions because of high rates of change in B. However, the largest reported dB/dt (Steens Mountain event) is estimated at 1 pT/day, seemingly too small to induce significant Faraday current density. Reversals may have also helped determine the nature of the interaction mechanism between GMF and living systems. Mechanisms based on fixed magnetic moments may not be capable of adapting to the reversal process. A better case can be made for an ion cyclotron resonance interaction. Direct involvement in the cell- signaling activities of biological ions would provide such flexibility, and also point to a broader role for the GMF in modulating CNS function than merely to provide orientation.

309

Copyright 0 1997 by Marcel Dekker, Inc.

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INTRODUCTION

LIBOFF

We have commented elsewhere (1) on the likelihood that all living things have an electromagnetic basis. In principle, this would describe genome expression in terms of unique electromagnetic (EM) field configurations instead of the more usual biological classifications based on categories of visible characteristics. Because of the distri- bution of charge and current that is innately part of every living organism, there is no question concerning the existence of such fields, only their intensity distributions.

In this view the evolution of any species is equivalent to changes in its charac- teristic EM field. Changes are brought about as responses to the external physical environment, with the understanding that the latter definition is extended to include also selective processes arising from competition.

To elaborate on this suggestion, we ask whether this also would mean that living things are more sensitive than previously suspected to changes in the EM environment. One major component of this environment is the geomagnetic field (GMF). There is at present increased interest regarding the extent to which the GMF is utilized by living things. Some of this interest stems from the emerging discovery that various organisms have the ability to synthesize domain-sized magnetite particles, apparently as a simple navigational aid (2). It is known that birds can detect aspects of the GMF (3) with remarkable sensitivity (4) although the underlying mechanism remains mysterious. At the same time, the puzzle of extremely low frequency (ELF) electromagnetic coupling to biological systems may involve a resonance mechanism ( 5 ) that depends on the simultaneous application of weak magnetostatic fields, in turn implying that some as yet unknown functional relationship to the GMF is involved. As an example, we recently (6) hypothesized a role for the GMF to help explain the epidemiological results (7) suggesting a link between 50/60-Hz power line magnetic fields and childhood leu- kemia. A number of theoretical analyses have been presented (8,9) claiming that these epidemiological cancer correlations and other observed bioelectromagnetic effects are unlikely because the fields involved are energetically well below thermal noise thresh- olds. However, if one believes the laboratory reports, these theoretical analyses may instead be regarded as compelling evidence that biological systems have evolved ex- quisitely sensitive means to utilize electromagnetic signaling.

In any event, if living systems are indeed especially sensitive to exogenous EM fields, one might expect that the GMF must have played a key role in evolution. Al- though it is clear that many organisms have adapted to the GMF, there has been re- markably little discussion concerning the larger evolutionary aspects of this question. It is in this context that we wish to explore the ways in which life on earth may have become sensitized to the GMF.

CHARACTERIZING THE GMF

The magnitudes of vector fields such as the GMF are specified either in terms of their components, e.g., those corresponding to the x-, y-, and z-directions, or, equiva- lently, as the total field intensity at that point, merely the square root of the sum of the squares of the three components. In common use are the group of parameters shown in Figure 1, namely the magnitude of the total field intensity, and the angles of declination and inclination. The total surface field intensity (BT) ranges from 660 mG at the

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GMF REVERSALS AND GENOME IMPRINTING 31 1

V

f r N

FIGURE 1. The geomagnetic field at the surface of the earth. Directions E and N correspond to geographic east and north, respectively. The vertical direction is indicated by the line VV. The earth’s radius vector r always points along VV. The total geomagnetic field intensity vector is given by BT, which makes an inclination angle I with the horizontal and a declination angle D with geographic north. Magnetic compass direction is NM.

geomagnetic poles to 240 mG at the geomagnetic equator. (Recall that 1 .0pT = 10 mG.) The GMF over the earth’s surface is composed of the so-called dipolefield, originating within the core of the earth, as well as additional local fields resulting from crustal contributions such as iron ores and human structures containing ferrous components.

Although for many purposes one can think of the GMF as constant (a constant magnetic field is also referred to as a DC or a magnetostatic field), there is no question that there are time variations in the GMF (10). These range from very low intensity micropulsations, with periods of the order of seconds, related to solar activity, through more gradual changes, occurring over hundreds of years, to the radical changes during reversals of the GMF, events separated by many hundreds of thousands, if not millions, of years ( 1 1).

Whatever biological effects that one might connect to the high-frequency variations in the GMF due to solar activity or to atmospheric electricity, ranging from about 0.001 Hz to 20 Hz (12), these must necessarily involve minuscule magnetic field changes, far smaller than 0.1 pT. On the other hand, the change in GMF following a reversal is substantially greater, of the order of 100 pT. Accordingly, we shall concen- trate on those effects that might conceivably be related to GMF reversals.

GEOMAGNETIC REVERSALS The latter are indeed profound events. To a first approximation, the entire dipole

moment of the earth reverses itself. The southern and northern magnetic poles are interchanged, such that each reversal results in all compasses pointing exactly opposite

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312 LIBOFF

to the direction obtained before the reversal. The period of time during which the GMF retains a given polarity is referred to as a chron. The last reversal (leading to the present Brunhes chron) occurred approximately 730,000 years ago (1 1). Interestingly, there is some evidence that the earth may be approaching another reversal, perhaps in one or two thousand years (13).

Reversals in the GMF may play an important role in evolution, with two poten- tially important periods of interest, the dwell time T of a given chron and the transition or switching time T between chrons. Figure 2a is an idealized plot of the way the GMF varies over long periods. Even though there may sometimes be more than a million years between reversals, the time interval over which the transition process itself occurs can last between five and ten thousand years. It is generally believed (11) that these transition periods are characterized by an unstable GMF, as the main dipole field at- tempts to reassert itself. During this changeover period, the magnitude of the ambient GMF drops to between zero and 10% of that magnetic field intensity occurring during normal or reversed chrons (Fig. 2b). Further, the field becomes excessively noisy, with rates of change (i.e., dB/dt) much greater than what is seen once the reversal has stabilized (Fig. 2c).

I dB /dt I

(c)

FIGURE 2. Geomagnetic reversals as a function of time, drawn in an idealized way. (a) Normal and reversed chrons persist for a time T. Transitions between chrons happen over a time 7. For convenience, the relative times for T and 7 are distorted. Actually T is approximately 1000 times greater than 7. (b) During transitions, the magnitude of B falls to approximately 10% of what it is during stable chrons. (c) During transition periods, the geomagnetic field, although weaker, develops instabilities with high rates of change dB/dt.

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GMF REVERSALS AND GENOME IMPRINTING 313

GMF REVERSALS AND THE GENOME

Even when life first began on earth, in excess of about 3.5 billion years ago, the GMF was already well established. It is clear that considerable time had elapsed for all living systems to have adapted accordingly. Further, if the genome does indeed reflect billions of years of adaptation to the GMF, it seems reasonable to expect that geomagnetic reversals must have played a role in this adaptation, in terms of both the long relatively stable periods between transitions and the short-period noisier transitions.

Let us make the convenient assumption that geomagnetic reversals occur, on the average, once every 350,000years. This implies that there may have been approximately 10,000 reversals over the course of living history. Although this number is probably a reasonable first-order average, magnetic reversals are by no means evenly distributed in time. There have been periods in the earth’s history when for tens of millions of years there were no reversals (14). These epochs are referred to as superchrons. Superchrons occurred, for example, prior to the Permian-Triassic and to the Cretaceous-Tertiary mass extinctions. It is conceivable that such long periods of magnetic stability might have resulted in exceptionally unusual biosensitivity to reversals.

How can one classify biologically relevant GMF reversal parameters? At first glance, it might seem that selective advantages based on the sign of the field, similar to those enjoyed presented by magnetotactic bacteria and perhaps by birds, would have to be reinitiated following each reversal. We shall refer to this type of GMF adaptation as (-1)” B-imprinting, where n is the sequential number of each reversal, and B the magnetic field vector. In the case of magnetotactic bacteria, reversal of the direction of the field, as studied by transporting Northern hemisphere GMF bacteria to the other side of the GMF equator (15,16), leads to a rather quick reassertion of the required dipole direction in the original Northern population. It appears that a small fraction of the Southern hemisphere GMF bacteria population is always expressed in the North- ern population, perhaps as a hedge against the next GMF reversal. Magnetotactic bacteria, to avoid potential difficulties arising from GMF reversals, appear to have been (-ly B-imprinted in the form of a simple strategy based on large numbers.

On the other hand, since only the direction of the field changes after each reversal, but the magnitude is unchanged, it can be argued that adaptations to merely the magnitude of the GMF will provide a less disruptive component of the physical environment for the genome to capture. We call this process I B I -imprinting. In (-ly B- imprinting the genome makes use of both the magnitude and the direction of the field. In the case of I B I -imprinting, only the magnitude is important.

The instability associated with the short-period transition process can play havoc with either type of imprinting. This becomes evident when the generation cycle time for biological organisms is compared with the length of the geomagnetic transition process, which, as pointed out above, is hardly instantaneous. We estimate that generation times can range from about 3 x lo4 years to 30 years. Assuming a mean of six thousand years for the time associated with an unstable transitional GMF, this corresponds to between 2 x lo7 and 200 cycles. Even in the middle of a stable chron, some animals are apparently very sensitive to the GMF, as evidenced by whale beaching, a phenomenon in which whales often follow magnetic field directions in the ocean bot- tom to their own destruction (17). It therefore seems reasonable to expect that a selective advantage dependent on either the sign of the field or its magnitude would likely

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atrophy over millions or even thousands of generations, if the field remained altered in both direction and magnitude for extended periods.

AVIAN NAVIGATIONAL COMPASS

Assume, as in Figure 2a that when the earth's field has stabilized following a reversal, the resulting dipole field is identical to the field before the reversal, except in sign. Forgetting, for the moment, the magnetic discontinuities occurring during the transition process, we ask whether it is possible to find a GMF parameter that is not dependent on the sign of the field. There is some evidence (18) that certain animals (sea turtles, newts) may be sensitive to the magnetic inclination angle I pictured in Figure 1, but not to the polarity of the magnetic field vector. It has been shown by Wiltschko and Wiltschko (19) that the avian navigational compass also utilizes the magnetic inclination, as well as the magnitude of the total field intensity and the direction of the horizontal component.

As indicated in Figure 1, the magnetic inclination is defined as equal to the angle between the axial direction of the magnetic field vector and the horizontal magnetic north-south direction. Under this definition, when the earth's total field vector reverses, the angle I merely changes sign, retaining the same value (e.g., goes from 66" to -66"). The Wiltschko hypothesis implies that the avian magnetic compass somehow determines only the magnitude of I, and not the sign.

We suggest another possibility, that the compass, instead of using the angle I, actually utilizes a function of I that does not change sign when the magnetic field is reversed. One such function is cos I. Consider Figure 3, which shows a vertical slice in the plane determined by the vertical VV and the horizontal direction vector of magnetic north N at any point on the surface of the earth. The total magnetic field vector B makes an angle I with respect to N. This angle remains the same following a magnetic reversal, since B and N are both reversed.

The scalar product between the two vectors N and B is defined as:

N*B = IN1 X IBI cos (N, B) (1)

Since (N, B), the angle between vectors N and B, is the same as the inclination I , we can write

N-B = IN1 X IBI COSI (2) This allows one to express the compass sensitivity to the GMF in a more general way that does not depend on the polarity of the field, but nevertheless readily encompasses the Wiltschko hypothesis. We shall call this type of GMF (angular) sensitivity N-B-imprinting. Under N-B imprinting, birds can use the same compass from one chron to the next.

Note that this magnetic compass will be of no use during transition periods, forc- ing birds to use other-than-magnetic compasses (e.g., solar, lunar, or stellar). Further, during stable chrons, the scalar product N-B is always zero at the geomagnetic poles and maximum at the geomagnetic equator (Fig. 4). This implies that the avian magnetic compass may be more effective at higher iatitudes, where small changes can be more readily discerned. Both facts are possible explanations as to why birds are imprinted with more than one compass.

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V

B

-" -B

V

FIGURE 3. Vertical plane containing magnetic north and the total GMF vector at any point on the earth's surface. The vertical direction is along W. The angle included between B and N is the magnetic inclination I. Vectors B and N both change by 180" under a magnetic reversal, such that the scalar product N-B remains invariant.

TRANSITIONS AND THE GENOME

Can additional arguments be made concerning the possibility of genetic modifi- cations resulting directly from the transition itself? We can imagine two types of effects that might be associated with transitions. In the first case, losing the GMF parameter imprinted during the most recent chron would be important, especially if this loss were

(GEOMAGNETIC) LATITUDE

90" (Polar

M i d - L a t i t u d e s

0" (Equatorial)

NORMAL (N*BV(INI x IBII

0

cos I

1

REVERSED (N*BI/IINI x IBI)

NAB 5L N

N

B -c- +

0

cos I

1

FIGURE 4. Relative orientations of N and B, and values of N-B at three geomagnetic latitudes, under normal and reversed chrons. The values of N-B have been divided by IN f x I B I to obtain, in each case, the resulting cosine of the angle of magnetic inclination. [See Eq. (2).]

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experienced over extremely long periods. There is some evidence that reducing the background magnetic field to extremely low levels can affect biological response. It has been reported (20) that the light/dark circadian periodicity of sparrows is altered when the GMF is reduced by a factor of lo3. In a more recent experiment (21) reduction of the GMF by a factor of lo4 resulted in developmental abnormalities in newt larvae.

Second, one can also imagine an altered biological response happening as a consequence of rapid changes in B. To describe these, it is simplest to use the rate of change dB/dt, an interesting parameter because of the experimental research that has been done in recent years, studying the biological effects of exposure to ELF magnetic fields. In the present case, the instabilities occurring as part of the transition process are probably nonperiodic, which likely precludes any chance of genetic adaptation to the GMF. Nevertheless, it is conceivable that rapid changes in the GMF could result in somatic effects. The immediate consequence of exposing living systems, which are elec- trically conducting, to rapidly changing magnetic fields is that electrical currents are formed within the system, in accord with Faraday’s Law of Induction. The greater dB/dt is, the larger the current. Also, the greater the conducting cross-sectional area, the greater is the induced current. Large animals, therefore, might be considered at greater risk than small ones, if indeed the actual rates of change of B were sufficient to induce physiologically significant currents.

Little information is available concerning the details of the transitions between paleomagnetic reversals, other than the fact that these can range up to lo4 years in length, exhibit average field levels up to perhaps 10% of the stable dipole field, and are far noisier than the stable chrons. One highly unstable period in GMF history, the Steens Mountain event, has been extensively studied. In a rather short time approximately 15.5 x 106years ago (22), a series of reversals occurred during which it has been estimated that the rate of change in the magnetic field reached levels as high as 1 pT/day (23,24). This number corresponds to an average of only 1 x 10-5pT/s. There is no telling if the number 1 pT/day itself represents an average of stops and starts, with periods of sharper and slower changes interspersed. However, the likelihood of much larger “instantaneous” values of dB/dt being measured at the earth’s surface seems remote, con- sidering the fact that the degree of eddy-current damping due to the conductivity of the mantle surrounding the core increases with dB/dt.

However rapid 1 x 10” pT/s may appear to the geologist, it is all but negligible to those studying bioelectromagnetic interactions. The best laboratory evidence, inter- preted liberally, suggests that biological changes cannot be connected to dB/dt values lower than about 1 pT/s. Although there is some evidence that intense changes in speciation are associated with GMF reversals (25), it is also well established that many reversals do not lead to speciation discontinuities (1 1).

One reason why some reversals may be more effective than others in this regard is that T, the transition period, can range from as little as tens of days up to tens of thousands of years. Presumably the longer periods of instability might have resulted in greater changes in speciation than very short periods, such as the Steens Mountain event. We therefore propose a figure of merit with which to examine potential correlations with biological effectiveness during paleomagnetic transitions, namely the product of dB/dt and the length of the transition, T dB/dt. In other words, if genetic changes do occur as a result of GMF transitions, they are expected to be more likely when large mean values of dB/dt prevail for long periods.

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POSSIBLE MECHANISMS

There is no question that many different types of organisms sequester magnetic iron oxide in the form of domain-sized particles. In the case of magnetotactic bacteria, the function of these particles is clearly navigational, to steer the bacteria to the layers of mud at lower depths. By no means is it as clear that higher organisms make use of magnetite particles in similar ways. The bacteria experience a mechanical torque while swimming that is proportional to the magnetic moment of the endogenously aligned magnetite. This torque in effect acts to line up the bacterial axis with the lines of force of the GMF. In order for the magnetic particles to convey information concerning direction in more massive organisms, say, birds, whales, bees, or humans, the torque on the particles found in these organisms would, first, have to be coherent and, second, be so small as to be of no mechanical consequence. Instead, the individual torques would have to somehow be detected by elements in the nervous system. Kirschvink et al., especially, have advocated this point of view, showing that there is a considerable concentration of such particles within the central nervous system of different species (26), and also suggesting a number of models by means of which the biological system might be sensitive to the torque on these particles.

An alternate way of explaining GMF sensitivity in living systems is through ion cyclotron resonance (ICR). In this case it is not the interaction of the GMF with the magnetic moment of endogenous magnetite particles that is critical, but rather the combined effect of the GMF and endogenous electric fields on biological ions such as Ca2+, Mg2+, K+, etc. (27). For example, low -frequency electrical oscillations occur both intracellularly and as long-range coherent modes in the central nervous system. Active and passive ion transport play key roles in these oscillations, and any effect on transport because of ion resonance coupling could act to modulate the oscillations and therefore affect physiological response.

The expression governing the ICR interaction sets the ratio of the EM frequency w to the magnitude of the GMF intensity B, equal to the charge-to-mass ratio of the ionic species that is being stimulated, as follows:

wlB = qlm (3) Note the connection to N-B imprinting. Let us assume that the source of the oscillation w is an endogenous electric field E(t) oscillating in the horizontal plane. For example, this might represent the low-frequency rhythmicity observed in the visual cortex (28). If this vector E(t) is contained within the horizontal plane, then it will always be at some angle to N that can be adjusted by the bird in flight, steering to the correct compass heading in the same manner as is done in planes or ships. On the other hand, one requirement for ICR is that the vectors B and E at least have components normal to one another (27). Therefore, N-B imprinting is consistent with an ICR mechanism. A bird flying parallel to the earth's surface that also generates an endogenous electric field polarized in the horizontal direction will be enabled, in principle, to sense the value of N-B, using ion cyclotron resonance.

In pursuing this model we also note that it leads to the GMF being connected to living systems in a more complete way than is possible by means of magnetite inclusions, suggesting the sort of special role for electromagnetic fields that was hinted at in the Introduction. There are good reasons for regarding the GMF as an intrinsic factor in cellular signaling, especially if the underlying interaction mechanism is a resonance

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effect. Much of the ELF biomagnetic research in reach years has pointed to GMF modulations of cell signaling, implying control over a potential range of physiological activities that is not limited to merely a directional response. It has been found that the GMF, acting through an ion cyclotron resonance interaction, can modulate the motility of diatoms (29), the regeneration rate of Planaria (30), bone growth (31), plant growth (32), and time discrimination (33) and learning (34) in rats. It is difficult to conceive of magnetite in living systems playing any biological role other than as a high magnetic moment compass material in simple organisms. Perhaps the greatest advantage in con- sidering a GMF mechanism that involves cell signaling is the greater plasticity that would be likely under the long-term changes that occur during transitions in the field.

We have also pointed out (27) that the GMF may play the role of zeitgeber in a biological clock mechanism if indeed it interacts in an ICR manner. The physics of resonance phenomena always lead to specific frequencies, and thus to specific timing possibilities. In this case the resonance frequency is solely a function of the strength of the GMF and the effective charge-to-mass ratios that are involved. Not only would this constitute a truly distributed biological clock, with no specific morphological basis, but it would also have the additional feature of being multidimensional, that is, having separate, but simultaneous timing modes for different ionic species.

CONCLUSIONS

The question of the sensitivity of living organisms to the GMF should be exam- ined with an eye to the 10,000 magnetic reversals that have occurred since life began. One can readily identify at least three functions of the GMF that conceivably might be genetically imprinted, I B 1 , (-ly B, and N-B, where the latter not only fits the Wiltschko hypothesis for the avian magnetic compass, but also describes an angular dependence that is invariant under magnetic reversals. Even if the genome could have adapted to a functional dependence that is independent of GMF polarity, there is a major problem connected to the transition times between one chron and the next, times sometimes as long as lo4 years. Two potential biological problems are connected to polarity transitions, the first being the discontinuity in GMF intensity. We speculate that the other- than-magnetic compasses known to be used by birds grew out of the need t o accom- modate to magnetic discontinuities during transitions. A second potential problem involves the possibility of physiologically significant induced current densities arising from the larger rates of change in the GMF that are known to occur during transitions. However, even the fastest reversal yet noted, the Steens Mountain event, is estimated to have resulted in an average rate of change of only lO-’pT/s, many orders of magnitude below the rates of change in B that are considered biologically significant. Al- though little is known about the instantaneous changes in B during reversal transitions, it is unlikely that higher rates are possible because of the limits placed on the magnitudes of such changes due to the damping effects of the earth’s crustal conductivity.

There is now good evidence that fields at GMF levels can modulate a wide range of biological response in different organisms by means of an ion cyclotron resonance mechanism. As far as we know, ICR mechanisms do not require the presence of magnetite particles. Further, such interactions likely occur within the electric field complex in cell-signaling pathways, allowing one to view the question of biosensitivity to the GMF in a far broader context than happens in the magnetic moment coupling to the

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GMF observed in magnetotactic bacteria. Cell signaling is a highly conserved function intrinsic to all living systems, and it would hardly be surprising to learn that these an- cient pathways have failed to notice the physical characteristics of the GMF.

Finally, we note that most of the emphasis in the growing body of research on magnetic bioeffects has been limited to ascertaining levels of risk and/or modeling possible interaction mechanisms, with very little thought given to the larger biological questions that surround these phenomena. We think it unreasonable to admit the possibility of interactions so weak that they have only recently been recognized without conceding that their mere existence must also signal a highly conserved biological function, one dependent on the GMF, and one that we have yet to fathom.

REFERENCES

1. Liboff, A.R.: Evolution and the change in electromagnetic state, Electro- Magne-

2. Blakemore, F.P.: Magnetotactic bacteria, Science 190,377-379, 1975. 3. Keeton, W.T.: Magnets interfere with pigeon homing, Proc. Natl. Acad. Sci. USA

4. Semm, P., and Beason, R.C.: Responses to small magnetic variations by trigeminal system of the bobolink, Brain Res. Bull. 25,735-740, 1990.

5. Liboff, A.R.: The “cyclotron resonance” hypothesis: experimental evidence and theoretical constraints, in Interaction Mechanisms of Low-Level Electromagnetic Fields in Living Systems, B. Norden and C. Ramel, eds., Oxford University Press, Oxford, 130-147, 1992.

6. Liboff, A.R., and McLeod, B.R.: Power lines and the geomagnetic field, Bioelec- tromagnetics 26,227-230, 1996.

7. Wertheimer, N., and Leeper, E.: Electrical wiring configuration and childhood cancer, Am. J. Epidemiol. 109,273-284,1979.

8. Weaver, J.C., and Astumian, R.D.: The response of living cells to very weak electric fields: the thermal noise limit, Science 247,459-462, 1990.

9. Adair, R.: Constraints on biological effects of weak extremely-low-frequency electromagnetic fields, Phys. Rev. A43, 1039-1048, 1991.

10. Skiles, D.D.: The geomagnetic field: its nature, history, and biological relevance, in Magnetite Biomineralization and Magnetoreception in Organisms, J.L. Kirschvin k, D.S. Jones, and B.J. MacFadden, eds., Plenum Press, New York, 1985.

11. Jacobs, J.A.: Reversals of the Earth’s Magnetic Field, 2nd ed., Cambridge University Press, New York, 1994.

12. Polk, C.: Sources, propagation, amplitude, and temporal variation of extremely low frequency (0-100 Hz) electromagnetic fields, in Biologic and Clinical Effects of Low- Frequency Magnetic and Electric Fields, J.G. Llaurado, A.Sances, Jr., and J.H. Bat- tocletti, eds., Charles C Thomas, Springfield, IL, 2148, 1974.

13. Coe, R.: A swiftly changing field, Nature 366,205-206, 1993. 14. Courtillot, V., and Besse, J.: Magnetic field reversals, polar wandering and core-

15. Blakemore, R.P., Frankel, R.B., and Kalmijn, A.J.: South-seeking magnetotactic

tobiol. 15,245-252, 1996.

68,102-106,1971.

mantle coupling, Science 237, 1140-1 147, 1987.

bacteria in the southern hemisphere, Nature 236,384-385, 1980.

Ele

ctro

mag

n B

iol M

ed D

ownl

oade

d fr

om in

form

ahea

lthca

re.c

om b

y U

nive

rsity

of

Cal

ifor

nia

Irvi

ne o

n 11

/07/

14Fo

r pe

rson

al u

se o

nly.

320 LIBOFF

16. Frankel, R.B., Blakemore, R.P., Torres de Araujo, F.F., Esquival, D.M.S., and Danon, J.: Magnetostatic bacteria at the geomagnetic equator, Science 212,1269- 1270,1981.

17. Kirschvink, J.L., Dizon, A.E., and Westphal, J.A.: Evidence from strandings for geomagnetic sensitivity in cetaceans, J. Exp. Biol. 120, 1-24, 1986.

18. Lohmann, K.J.: Magnetic compass orientation, Nature 362,703, 1993. 19. Wiltschko, W., and Wiltschko, R.: Magnetic compass of European robins, Science

20. Bliss, V.L., and Heppner, F.H.: Circadian activity rhythm influenced by near zero magnetic field, Nature 261,411-412, 1976.

21. Asashima, M., Shimada, K., and Pfeiffer, C.J.: Magnetic shielding induces early developmental abnormalities in the newt, Cynops pyrrhoguster, Bioelectromagnet- ics 12, 215-224, 1991.

22. Watkins, N.D.: Paleomagnetism of the Columbia plateaus, J. Geophys. Res. 70, 1379,1965.

23. Coe, R.S., and Prevot, M.: Evidence suggesting extremely rapid field variation during a magnetic reversal, Earth Planet. Sci. Lett. 92,292, 1989.

24. Coe, R.S., Prevot, M., and Camps, P.: New evidence for extraordinarily rapid change of the geomagnetic field during a reversal, Nature 374,687-692, 1995.

25. Hays, J.D.: Faunal extinctions and reversals of the earth’s magnetic vield, Geol. SOC. Am. Bull. 82,2433-2447,1971.

26. Kirschvink, J.L., Kobayashi-Kirschvink, and Woodford, B.J.: Magnetite biomineralization in the human brain, Proc. Natl. Acad. Sci. USA 89,7683-7687, 1992.

27. ‘Liboff, A.R.: Electric-field ion cyclotron resonance, Bioelectromagnetics 18, 85- 87, 1997.

28. Traub, R.D., Whittington, M.A., Stanford, I.M., and Jefferys, J.G.R.: A mechanism for generation of long-range synchronous fast oscillations in the cortex, Nature 383,621424,1996.

29. Smith, S.D., McLeod, B.R., Liboff, A.R., and Cooksey, K.E.: Calcium cyclotron resonance and diatom motility, Bioelectromagnetics 8,215-227, 1987.

30. Jenrow, K.A., Smith, C., and Liboff, A.R.: Weak ELF fields and regeneration in the planarian Dugesiu tigrinu, Bioelectromagnetics 16, 106-112, 1995.

31. Diebert, M.C., McLeod, B.R., Smith, S.D., and Liboff, A.R.: Ion resonance electromagnetic field stimulation of fracture healing in rabbits with a fibular ostectomy, J. Orthoped. Res. 12,878-885,1994.

32. Thomas, J.R., Schrot, J., and Liboff, A.R.: Low-intensity magnetic fields alter op- erant behavior in rats, Bioelectromagnetics 7,349-357, 1986.

33. Smith, S.D., McLeod, B.R., and Liboff, A.R.: Effects of CR-tuned 60 Hz-magnetic fields on sprouting and early growth of Ruphunus sutivus, Bioelectrochem. Bioen- ereget. 32,67-76, 1993.

34. Lovely, R.H., Creim, J.A., Miller, D.L., and Anderson, L.E.: Behavior of rats in a radial arm maze during exposure to magnetic fields: evidence for effects of mag- nesium ion resonance, 12th Annual Meeting of Bioelectromagnetics Society, Los Angeles, 1993, Abstract E-1-6.

176,62-64, 1972.

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Geomagnetic Reversals and Genome Imprinting