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Magma contains many materials which are magnetically affected. When this magma is ejected from the mantle and begins forming new crust, these materials align to the earth's magnetic field. The crust hardens, and the magnetic alignment is fixed (just as in normal magnets, made by using a similar process)
Geomagnetic polarity since the middle Jurassic. Dark areas denote periods where the polarity matches today's polarity, light areas denote periods where that polarity is reversed.
NASA computer simulation using the model of Glatzmaier and Roberts. The tubes represent magnetic field lines, blue when the field points towards the center and yellow when away. The rotation axis of the Earth is centered and vertical. The dense clusters of lines are within the Earth's core
The arrival of continental slabs carried down into the mantle by the action of plate tectonics at subduction zones or the initiation of new mantle plumes from the core-mantle boundary.
geomagnetic intensity has declined almost continuously from a maximum 35% above the modern value achieved approximately 2,000 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
Variations in virtual axial dipole moment since the last reversal.
Originally posted by Chadwickus
Nice thread.
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Originally posted by BruceEFury
Another theory is, as are solar system moves closer to a different hemisphere of our galaxy,
the dense center of the milkyway will eventually reverse the gravitational field of our planet.
Originally posted by alfa1
Originally posted by BruceEFury
Another theory is, as are solar system moves closer to a different hemisphere of our galaxy,
the dense center of the milkyway will eventually reverse the gravitational field of our planet.
No, seriously, I have to pull you up on that.
What you said makes no sense at all, either scientifically or even science fictionally.
Originally posted by BruceEFury
Hmm... Okay. Do your research pale before you start attacking me.
geological pole flip
No form of the hypothesis is accepted amongst the scientific community. There is evidence of precession and changes in axial tilt, but this change is on much longer time-scales and does not involve relative motion of the spin axis with respect to the planet. However, in what is known as true polar wander, the solid Earth can rotate with respect to a fixed spin axis. Research shows that during the last 200 million years a total true polar wander of some 30° has occurred, but that no super-rapid shifts in the Earth's pole were found during this period.
Over the past 150 years, the main (axial dipole) component of the Earth’s magnetic field has decayed by nearly 10%, a rate ten times faster than if the dynamo were simply switched off. To that extent, the dynamo today is operating more as an anti-dynamo, a destroyer of the dipole part of the field. Intriguingly, this decay rate is characteristic of magnetic reversals, which paleomagnetic observations have shown occur on average, though with great variability, about once every half million years
emphasis mine
Geographically, the recent dipole decay is largely due to changes in the field beneath the South Atlantic Ocean. This pattern is connected to the growth of the South Atlantic Magnetic Anomaly, an area in which the field at the Earth’s surface is now about 35% weaker than would be expected. This hole in the field has serious implications for lowEarth-orbit satellite operations since it impacts the radiation dosage at these altitudes. How much longer will the South Atlantic Magnetic Anomaly continue to grow? How large will it become? Is the field reversing? These questions currently cannot be answered because the mechanism by which the Earth’s magnetic field is generated is only partially understood.
The Earth’s magnetic field originates in the fluid outer core, where self-regenerating dynamo action maintains the field against decay. This field gives rise to both permanent and induced magnetization in crustal rocks and also interacts with current systems in the ionosphere and magnetosphere (space weather). These interactions give rise to fluctuating external electromagnetic fields that in turn induce electric currents in the Earth’s conducting interior. The induced electric currents produce time-variable electromagnetic fields at and above the Earth’s surface, and the field measured at any point represents the vector sum of contributions from the core field, the crustal field, the external field, and the induced electromagnetic field.