Geomagnetic excursion
From Wikipedia, the free encyclopedia
A geomagnetic excursion, like a geomagnetic reversal, is a significant change in the Earth's magnetic field.
Unlike reversals however, an excursion does not permanently change the
large-scale orientation of the field, but rather represents a dramatic,
typically short-lived decrease in field intensity, with a variation in
pole orientation of up to 45 degrees from the previous position. These
events, which typically last a few thousand to a few tens of thousands
of years, often involve declines in field strength to between 0 and 20%
of normal. Excursions, unlike reversals, are generally not recorded
across the entire globe. This is partially due to them not being
recorded well within the sedimentary record, but also because they
likely do not extend through the entire geomagnetic field. One of the
first excursions to be studied was the Laschamp event,
dated at around 40,000 years ago. Since this event has also been seen
in sites across the globe, it is suggested as one of the few examples of
a truly global excursion.[1]
The work of David Gubbins suggests that excursions occur when the magnetic field is reversed only within the liquid outer core; reversals occur when the inner core is also affected.[2] This fits well with observations of events within the current chron of reversals taking 3–7000 years to complete, while excursions typically last 500–3000 years. However, this timescale does not hold true for all events, and the need for separate generation of fields has been contested, since the changes can be spontaneously generated in mathematical models.
A minority opinion, held by such figures as Richard A. Muller, is that geomagnetic excursions are not a spontaneous processes but rather triggered by external events which directly disrupt the flow in the Earth's core. Such processes may include the arrival of continental slabs carried down into the mantle by the action of plate tectonics at subduction zones, the initiation of new mantle plumes from the core-mantle boundary, and possibly mantle-core shear forces and displacements resulting from very large impact events. Supporters of this theory hold that any of these events lead to a large scale disruption of the dynamo, effectively turning off the geomagnetic field for a period of time necessary for it to recover.
Except for recent periods of the geologic past, it is not well known how frequently geomagnetic excursions occur. Unlike geomagnetic reversals, which are easily detected by the change in field direction, the relatively short-lived excursions can be easily overlooked in long duration, coarsely resolved, records of past geomagnetic field intensity. Present knowledge suggests that they are around ten times more abundant than reversals, with up to 12 excursions documented within the current reversal period Brunhes–Matuyama reversal.
Since no excursions have been recorded within human history, it is
unknown precisely what effects one would have. However, it is likely
that nothing serious would occur, as the human species has certainly
lived through at least one such event; Homo erectus and possibly Homo heidelbergensis
lived through the Matuyama reversal with no known ill effect, and
excursions are shorter lived and do not result in permanent changes to
the magnetic field. The major hazard to modern society is likely to be
similar to those associated with geomagnetic storms,
where satellites and power supplies may be damaged, although compass
navigation would also be affected. Some forms of life which are thought
to navigate based on magnetic fields may be disrupted, but again it is
suggested that these species have survived excursions in the past. Since
excursion periods are not always global, any effect might well only be
experienced in certain places, with others relatively unaffected. The
time period involved could be as little as a century, or as much as
10,000 years.
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Causes
Scientific opinion is divided on what caused geomagnetic excursions. The dominant theory is that they are an inherent aspect of the dynamo processes that maintain the Earth's magnetic field. In computer simulations, it is observed that magnetic field lines can sometimes become tangled and disorganized through the chaotic motions of liquid metal in the Earth's core. In such cases, this spontaneous disorganization can cause decreases in the magnetic field as perceived at the Earth's surface. In truth, under this scenario, the Earth's magnetic field intensity does not significantly change in the core itself, but rather energy is transferred from a dipole configuration to higher order multipole moments which decay more rapidly with the distance from the Earth's core, so that the expression of such a magnetic field at the surface of the Earth would be considerably less, even without significant changes in the strength of the deep field. This scenario is supported by observed tangling and spontaneous disorganizations in the solar magnetic field. However, this process in the sun invariabily leads to a reversal of the solar magnetic field (see: solar cycle), and has never been observed such that the field would recover without large scale changes in field orientation.The work of David Gubbins suggests that excursions occur when the magnetic field is reversed only within the liquid outer core; reversals occur when the inner core is also affected.[2] This fits well with observations of events within the current chron of reversals taking 3–7000 years to complete, while excursions typically last 500–3000 years. However, this timescale does not hold true for all events, and the need for separate generation of fields has been contested, since the changes can be spontaneously generated in mathematical models.
A minority opinion, held by such figures as Richard A. Muller, is that geomagnetic excursions are not a spontaneous processes but rather triggered by external events which directly disrupt the flow in the Earth's core. Such processes may include the arrival of continental slabs carried down into the mantle by the action of plate tectonics at subduction zones, the initiation of new mantle plumes from the core-mantle boundary, and possibly mantle-core shear forces and displacements resulting from very large impact events. Supporters of this theory hold that any of these events lead to a large scale disruption of the dynamo, effectively turning off the geomagnetic field for a period of time necessary for it to recover.
Except for recent periods of the geologic past, it is not well known how frequently geomagnetic excursions occur. Unlike geomagnetic reversals, which are easily detected by the change in field direction, the relatively short-lived excursions can be easily overlooked in long duration, coarsely resolved, records of past geomagnetic field intensity. Present knowledge suggests that they are around ten times more abundant than reversals, with up to 12 excursions documented within the current reversal period Brunhes–Matuyama reversal.
Effects
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This section does not cite any references or sources. (March 2010) |
Possible relationship to climate
There is evidence that geomagnetic excursions may be associated with episodes of rapid short-term climatic cooling during periods of continental glaciation (ice ages).[3]Notes and references
- ^ Roperch, P.; Bonhommet, N., Levi, S. (1988). "Paleointensity of the earth's magnetic field during the Laschamp excursion and its geomagnetic implications". Earth and Planetary Science Letters 88 (1-2): 209–219. Bibcode:1988E&PSL..88..209R. doi:10.1016/0012-821X(88)90058-1.
- ^ Gubbins, David (1999). "The distinction between geomagnetic excursions and reversals". Geophysical Journal International 137 (1): F1–F4. Bibcode:1999GeoJI.137....1C. doi:10.1046/j.1365-246X.1999.00810.x. Retrieved 19 April 2012.
- ^ Rampino, Michael R. (1979). "Possible relationships between changes in global ice volume, geomagnetic excursions, and the eccentricity of the Earth's orbit". Geology 7 (12): 584–587. Bibcode:1979Geo.....7..584R. doi:10.1130/0091-7613(1979)7<584:prbcig>2.0.CO;2.
- Valet, Jean-Pierre; Valladas, Hélène (2010). "The Laschamp-Mono lake geomagnetic events and the extinction of Neanderthal: a causal link or a coincidence?". Quaternary Science Reviews 29 (27-28): 3887–3893. Bibcode:2010QSRv...29.3887V. doi:10.1016/j.quascirev.2010.09.010.
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Wikipedia Geomagnetic Excursions
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Wikipedia Geomagnetic Excursions
So, if I extrapolate on what is being said here, it might be likely that when Mastodons were found in Alaska with spring flowers still in their mouths after being frozen solid suddenly that this is possibly from a sudden effect of a Geomagnetic excursion. So, possibly what happens in "The Day After Tomorrow" could be a potential real effect in some areas from a the "potential Geomagnetic Excursion" we started going into around 1900 when the magnetic north starting speeding up to now 40 miles per year heading out of Canada and towards Siberia.
If this is true we may be now experiencing Global Warming but if people start migrating north will they be one day, "Suddenly frozen like the mastodons were" too if they are outside when it happens?
Of course this is all theoretical at this point. But, if it happened before during a Geomagnetic Excursion and it is proven that we are now in another geomagnetic excursion then this kind of event or events likely are in our future at some point or points in time.
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Wikipedia Geomagnetic Excursions
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Possible relationship to climate
There is evidence that geomagnetic excursions may be associated with episodes of rapid short-term climatic cooling during periods of continental glaciation (ice ages).[3]end partial quote from:
Wikipedia Geomagnetic Excursions
So, if I extrapolate on what is being said here, it might be likely that when Mastodons were found in Alaska with spring flowers still in their mouths after being frozen solid suddenly that this is possibly from a sudden effect of a Geomagnetic excursion. So, possibly what happens in "The Day After Tomorrow" could be a potential real effect in some areas from a the "potential Geomagnetic Excursion" we started going into around 1900 when the magnetic north starting speeding up to now 40 miles per year heading out of Canada and towards Siberia.
If this is true we may be now experiencing Global Warming but if people start migrating north will they be one day, "Suddenly frozen like the mastodons were" too if they are outside when it happens?
Of course this is all theoretical at this point. But, if it happened before during a Geomagnetic Excursion and it is proven that we are now in another geomagnetic excursion then this kind of event or events likely are in our future at some point or points in time.
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