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Bioelectromagnetism

 

 

 

shifs in the GMF, has forced scientists to revise magnetic models that guide navigation. Te scientists

are working to understand why the GMF is changing so dramatically. Geomagnetic pulses, like the one

that happened in 2016, might be traced back to “hydromagnetic” waves arising from deep in the core

(Aubert, 2018). And the fast motion of the N magnetic pole could be linked to a high-speed jet of liquid

iron beneath Canada (Livermore et al., 2017). Many geomagnetic excursions tend to occur during the

period of low GMF intensity. Most of the known geomagnetic excursions contain GMF reversals, and

the GMF strength is greatly reduced as much as the GMF reversals (Ferk and Leonhardt, 2009). Te dif­

ferences between excursions and reversals are that the duration of the excursions is as short as 1–2 kyr or

less, and the observed GMF fuctuations of the excursions are regional. In the case of the GMF reversals,

global intensity variations appear more coherent (Brown et al., 2007). Not only GMF reversals but also

known excursions always occur when the magnetic dipole component (the main key player in the GMF

generation) reduced to <50% of its strength (Guyodo and Valet, 1999). Tis suggests that reversals and

excursions are not sudden abnormal phenomena, but stochastic phenomena that occur in the rhythm

of the geodynamo itself. Using the observed GMF model over the past 7 kyr, it has been confrmed that

when the magnetic dipole intensity is reduced to 50% or less, the non-dipole intensity increases rela­

tive to the dipole intensity, and eventually, geomagnetic excursion occurs (Brown et al., 2007; Valet and

Plenier, 2008).

Te most representative geomagnetic excursion known today is the “Laschamp excursion” about

41–42 kyr ago (41–42 ka, range: 41,4 ± 2 ka) during the end of the Last Glacial Period, and was frst rec­

ognized in the late 1960s as a GMF reversal (Bonhommet and Babkine, 1967). Te name of Laschamp

comes from the place Laschamp lavafows in the Clermont-Ferrand district of France (Chaîne des Puys,

France), where Brunhes lived. Te Laschamp excursion is said to have occurred at the time of the weak­

est GMF in the last 100 ka, and it is reported that the GMF strength at that time dropped to nearly 10%

of the current strength level.

Geodynamo simulations have suggested “pessimistic” and “optimistic” predictions for the life on

Earth regarding the consequences of decrease in the GMF. Generally speaking, as mentioned above, the

GMF protects the life on Earth from harmful rays from the universe. Terefore, if the GMF decreases

too much, it will be harmful to many lives on Earth, including humans. It is predicted that the magnetic

pole may be exchanged, and the GMF reversal transition can occur unexpectedly in a short time scale;

one surprisingly abrupt “centennial reversal transition” occurred in 144 ± 58 years (2σ) (Chou et al.,

2018). By investigating the structure of rocks on ancient Earth, Chinese geologists reported that the

S and N poles had already swapped places, and the reversing process has recently begun again (Chou

et al., 2018). Te frst sign of magnetic pole reversal is attributed to the weakening of the GMF intensity

(Chou et al., 2018). It is found that the GMF has weakened by 15% in the last 200 years and is becom­

ing more and more unstable (Chou et al., 2018). However, it is impossible to predict the specifc time of

reversal (Chou et al., 2018). Tis is because it is very difcult to know whether the weakening of the GMF

is sudden or gradual (Chou et al., 2018). It has been warned that the Earth will lose its barriers from the

solar wind and GCRs during a magnetic pole change (Chou et al., 2018). Consequently, it may cause a

rapid change in the fora and fauna on Earth and may have a very harmful efect on humans (Chou et al.,

2018). In addition, all digital technology will be destroyed and artifcial satellites and power lines will

fail (Chou et al., 2018). Te Earth will be exposed to the powerful solar wind, lose water, be bombarded

by “γ-ray burst,” and experience the same environmental conditions as Mars today, with a signifcant

loss of the GMF due to pole shif (Brown et al., 2007; Valet and Plenier, 2008; Ferk and Leonhardt, 2009).

6.3.5 The Extinction of Neanderthals

Te following hypothesis concerning the Laschamp excursion has recently been proposed for the

relationship between the geomagnetic excursion and the extinction of living organisms. It has been

hypothesized that the Laschamp excursion was associated with the extinction of Neanderthals, Homo

neanderthalensis in Europe as shown in Figure 6.7 (Channell and Vigliotti, 2019).