Effects on biosphere
Shortly after the first geomagnetic polarity time scales were produced, scientists began exploring the possibility that reversals could be linked to extinctions. Most such proposals rest on the assumption that the Earth's magnetic field would be much weaker during reversals. Possibly the first such hypothesis was that high energy particles trapped in the Van Allen radiation belt could be liberated and bombard the Earth.[37][38] Detailed calculations confirm that, if the Earth's dipole field disappeared entirely (leaving the quadrupole and higher components), most of the atmosphere would become accessible to high energy particles, but would act as a barrier to them, and cosmic ray collisions would produce secondary radiation of beryllium-10 or chlorine-36. An increase of beryllium-10 was noted in a 2012 German study showing a peak of beryllium-10 in Greenland ice cores during a brief complete reversal 41,000 years ago which led to the magnetic field strength dropping to an estimated 5% of normal during the reversal.[2] There is evidence that this occurs both during secular variation[39][40] and during reversals.[41][42]Another hypothesis by McCormac and Evans assumes that the Earth's field would disappear entirely during reversals.[43] They argue that the atmosphere of Mars may have been eroded away by the solar wind because it had no magnetic field to protect it. They predict that ions would be stripped away from Earth's atmosphere above 100 km. However, the evidence from paleointensity measurements is that the magnetic field does not disappear. Based on paleointensity data for the last 800,000 years,[44] the magnetopause is still estimated to be at about 3 Earth radii during the Brunhes-Matuyama reversal.[37] Even if the magnetic field disappeared, the solar wind may induce a sufficient magnetic field in the Earth's ionosphere to shield the surface from energetic particles.[45]
Hypotheses have also been advanced linking reversals to mass extinctions.[46] Many such arguments were based on an apparent periodicity in the rate of reversals; more careful analyses show that the reversal record is not periodic.[16] It may be, however, that the ends of superchrons have caused vigorous convection leading to widespread volcanism, and that the subsequent airborne ash caused extinctions.[47]
Tests of correlations between extinctions and reversals are difficult for a number of reasons. Larger animals are too scarce in the fossil record for good statistics, so paleontologists have analyzed microfossil extinctions. Even microfossil data can be unreliable if there are hiatuses in the fossil record. It can appear that the extinction occurs at the end of a polarity interval when the rest of that polarity interval was simply eroded away.[21] Statistical analysis shows no evidence for a correlation between reversals and extinctions.[48][37]
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- A geomagnetic reversal is a change in a planet's magnetic field such that the positions of magnetic north and magnetic south are interchanged. The Earth's field has ...Since people have become more interested in Geomagnetic Reversals, this site has done a lot of backpedaling on extinctions caused by a Reversal.This makes me question the motivations for changing this information. Is the motivation to calm the fears of the general public or actually based upon real science? So, is it being politically correct (in other words a lie to calm down the public) or is it based in fact and in real research?More and more scientists are talking like we are in a Reversal. You know this when people start saying things like "We might be entering into a reversal during the next 2000 years, the evidence being a 5% decrease in the magnetosphere every 10 years now."So, I think mostly the way this is written to avoid a panic over the planet, in much the same way governments tried to tamp down views on Global Warming the last 30 to 40 years.So, as we watch people die all over the earth by the hundreds and thousands now from Global Warming we might now also be watching (simultaneously) people actually dying from the Reversal we likely have been in 1900 or 1800 already.
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