Dear Friends of Science and Geology,

Is Geomagnetic reversal theory correct or just a guess??
http://en.wikipedia.org/wiki/Geomagnetic_reversal
As the theory is based on the Observing past fields, Past field reversals can be
and have been recorded in the "frozen" ferromagnetic (or more accurately,
ferrimagnetic) minerals of solidified sedimentary deposits or cooled volcanic
flows on land.
Has any one tried to keep two magnets parallel to each other? eg N & N and S & S
together in natural way with out any binding external force? in nature two
magnets never remain in parallel due to similar polarity expel the other similar
polarity. but if the First magnet is in direction of the Earth magnetic field
showing N & S magnetic poles and other similar magnet is brought to close to the
first magnet one has to change the direction from S => N. say if the first
magnet is fixed in position second magnet will show poles reversed.
Similarly when first Lava eruption occurs will show magnetic direction as
natural Earths magnetic fields and that becomes fixed as it solidifies. But any
subsequent lava eruption will never show the same direction as the previous
layer of lava magnetic direction but in reverse direction.(Previous layer of
LAVA acts as first fixed magnet) and that trend will follow on in any subsequent
lava eruption with each layer of Lava will show the Reversal of magnetic fields
even though earth magnetic field do not change.

So there is no question of changing Earth magnetic polarity. is looks just a
guess from science but in fact lava layers are always laid with reversal of
magnetic fields even though the time interval is short or long and that is why
the theory also has no regular time scale. do you think that Earth is so
irregular to change its magnetic fields - No way and there is no chance to
change the direction of earths magnetosphere or earths direction to move on
axis.


FROM YOURS Dr.BHUDIA-Science Group Of INDIA.
http://uk.groups.yahoo.com/group/venustransit_2004/
President:"Kutch Science Foundation".
Founder :"Kutch Amateurs Astronomers Club - Bhuj - Kutch".
Life Member:"kutch Itihaas Parishad".
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From Wikipedia, the free encyclopedia
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Recent geomagnetic reversals.
A geomagnetic reversal is a change in the orientation of Earth's magnetic field
such that the positions of magnetic north and magnetic south become
interchanged. These events, which typically last a few hundred to a few
thousands years, often involve an extended decline in field strength followed by
a rapid recovery after the new orientation has been established.

Contents
[hide]
a.. 1 History
b.. 2 Causes
c.. 3 Observing past fields
d.. 4 The geomagnetic polarity time scale
e.. 5 Future of the present field



[edit]
History
Over very long periods, geomagnetic reversals seems to have occurred with a
frequency of 1 to 5 events per million years; however, this duration is highly
variable. During some periods of geologic time (e.g. Cretaceous long normal),
the Earth's magnetic field is observed to maintain a single orientation for tens
of millions of years. Other events seem to have occurred very rapidly, with more
than one reversal in 50,000 years. The last reversal was the Brunhes-Matuyama
reversal approximately 780,000 years ago.

[edit]
Causes
Scientific opinion is divided on what causes geomagnetic reversals. Many
scientists believe that reversals are an inherent aspect of the dynamo theory of
how the geomagnetic field is generated. 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 some simulations, this leads to an instability in which the magnetic field
spontaneously flips over into the opposite orientation. This scenario is
supported by observations of the solar magnetic field, which undergoes
spontaneous reversals every 7-15 years (see: solar cycle). However, with the sun
it is observed that the solar magnetic intensity greatly increases during a
reversal, whereas all reversals on Earth seem to occur during periods of low
field strength.

Present computational methods have used very strong simplifications in order to
produce models that run to acceptable time scales for research programmes.

A minority opinion, held by such figures as Richard A. Muller, is that
geomagnetic reversals are not 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 resulting from very large impact events. Supporters of this theory hold
that any of these events could lead to a large scale disruption of the dynamo,
effectively turning off the geomagnetic field. Since the field is stable in
either the present North-South orientation or a reversed orientation, they
propose that when the field recovers from such a disruption it spontaneously
chooses one or the other state, such that a recovery is seen as a reversal in
about half of all cases. Brief disruptions which do not result in reversal are
also known and are called geomagnetic excursions.

[edit]
Observing past fields
Past field reversals can be and have been recorded in the "frozen" ferromagnetic
(or more accurately, ferrimagnetic) minerals of solidified sedimentary deposits
or cooled volcanic flows on land. Originally, however, the past record of
geomagnetic reversals was first noticed by observing the magnetic stripe
"anomalies" on the ocean floor. Since the sea floor spreads at an essentially
constant rate, this results in broadly evident "stripes" from which the past
magnetic field polarity can be inferred by looking at the data gathered from
simply towing a magnetometer along the sea floor. However, since no existing
unsubducted sea floor (or sea floor thrust onto continental plates, such as in
the case of ophiolites) is much older than about 180 Mya in age, other methods
are necessary for detecting older reversals. Most sedimentary rocks incorporate
tiny amounts of iron rich minerals, whose orientation is influenced by the
ambient magnetic field at the time at which they formed. Under favorable
conditions, it is thus possible to extract information of the variations in
magnetic field from many kinds of sedmentary rocks. However, subsequent
diagenetic processes after burial may erase evidence of the original field.

Because the magnetic field is present globally, finding similar patterns of
magnetic variations at different sites is one method used to correlate age
across different locations. In the past four decades great amounts of
paleomagnetic data have accumulated for about current seafloor ages (0 to ~250
Mya) to such an extent that such data have become an important and convenient
tool used to estimate the age of geologic sections in the field. It is, however,
not an independent dating method, but is dependent on absolute age dating
methods like radioisotopic systems to derive numeric ages. It has become
especially useful to metamorphic and igneous geologists where the use of index
fossils to estimate ages is seldom available.

[edit]
The geomagnetic polarity time scale

Record of Geomagnetic Polarity for ages 0-160 Mya. Reproduced from Lowrie(1997),
"Fundamentals of Geophysics".
The changing frequency of geomagnetic reversals over time
The Cretaceous Long Normal Superchron
The "Jurassic Quiet Zone"
[edit]
Future of the present field

Geomagnetic variations since the last reversal.
At present, the overall geomagnetic field is becoming weaker at a rate which
would, if it continues, cause the dipole field to temporarily collapse by
3000-4000 AD. (See: 1). The South Atlantic Anomaly is believed by some to be a
product of this. The present strong deterioration corresponds to a 10-15%
decline over the last 150 years and has accelerated in the past several years;
however, geomagnetic intensity has declined almost continuously from a maximum
35% above the modern value achieved approximately 2000 years ago. The rate of
decrease and the current strength are within the normal range of variation, as
shown by the record of past magnetic fields recorded in rocks.

One should note that no one knows if field decay will continue in the future.
Since a magnetic field reversal has never been observed by humans and the
mechanism of field generation is not well understood, it is difficult to say
what the characteristics of the magnetic field might be leading up to such a
reversal. Some speculate that a greatly diminished magnetic field during a
reversal period will expose the surface of the earth to a substantial and
potentially damaging increase in cosmic radiation. However, Homo erectus and
their ancestors certainly survived many previous reversals. There is no
uncontested evidence that a magnetic field reversal has ever caused any
biological extinctions. A possible explanation is that the solar wind may induce
a sufficient magnetic field in the Earth's ionosphere to shield energetic
particles even in the absence of the Earth's normal magnetic field [1].

The Earth's magnetic north pole is drifting from northern Canada towards Siberia
with a presently accelerating rate [2]. It is also unknown if this drift will
continue to accelerate.

Although the inspection of past reversals does not indicate biological
extinctions, present society with its reliance of electricity and
electromagnetic effects (e.g. radio, satellite communications) may be vulnerable
to technological disruptions in the event of a full field reversal.


Glatzmaier and collaborator Paul Roberts of UCLA have made a numerical model of
the electromagnetic, fluid dynamical processes of Earth's interior, and computed
it on a Cray supercomputer. The results reproduced key features of the magnetic
field over more than 40,000 years of simulated time. To top it off, the
computer-generated field reversed itself.[3]


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