Paleomagnetologist Michael Fuller is an emeritus professor from University of California, Santa Barbara and now a senior researcher at the University of Hawaii's School of Earth Science and Technology in its Institute of Geophysics and Planetology. His research has concentrated on polar shifts from the magnetic records trapped in Hawaiian lavas and on corings from the sea bed. Here is his explanation.
We know from magnetic records locked in rocks that the Earth's magnetic field has reversed many times in the past. We don't really know why but we have some theories that are being borne out in mathematical models.
We also know that the magnetic field of the sun reverses as well-- every 11 years, whereas the Earth's
reverses irregularly. The last geomagnetic reversal for Earth was about 780,000 years ago. The historic
reversal rate for Earth seems to be once every few hundred thousand years, but it has varied widely; on at
least two occasions, the field has maintained one polarity for tens of millions of years.
 Image: National Geophysical Data Center GEODYNAMO. Motion in the Earth's liquid core generates the planet's
magnetic field. |
Thus, the only two magnetic fields for which we have any significant historical record--those of the Earth and the sun--are bistable. They spend most of the time in a stable state with the magnetic field aligned roughly with the spin axis. The form of the stable geomagnetic field is like that of a bar magnet at the center of the Earth. It is what is called a dipole field--with a north and south pole. But occasionally this dipole field switches polarity--north and south reverse--and this process seems to take a few thousand years.
The Earth's field, like the sun's, is produced by dynamo action, which involves two processes. The first is the creation of new magnetic fields from the ambient geomagnetic field. This "field regeneration" takes place because magnetic field lines are trapped in good electrical conductors, such as the molten iron of the Earth's outer core. As Michael Faraday demonstrated, movement of a field line is impeded by an electrical current flowing to oppose that change. Because the molten iron in the core is a good electrical conductor, the field is trapped in the fluid--the frozen field effect. The field is carried along with the fluid as it moves in response to the forces imposed upon it. As the core moves, the field lines are stretched and twisted, and a new magnetic field is created.
 Image: National Geophysical Data Center DIPOLE MAGNET. The magnetic field resembles one that would be produced
by a giant bar magnet in the core of the Earth. |
The balance between these two processes determines the evolution of the magnetic field--namely, whether the field decays away or is regenerated. On the large scale of stars and planets, the field lines are caught up in the fluid motion and distorted. They then generate a new magnetic field before they diffuse away.
The geomagnetic field varies continuously. The decay time for the main dipole part of the geomagnetic field, whose constancy and simple geometry permits navigation by magnetic compasses, is probably in the neighborhood of 15,000 years. The largest part of this variation involves smaller features in the non-dipole field, which have smaller time constants and more complicated geometries. The variation must presumably arise from small changes in either of the two processes which give the dynamo action, or both.
See what we're tweeting about
3 Comments
Add Commenthello, as a layman i would like too ask what effects on humans would their be in a reversal of the magnetic fields, i understand this would not be a instant effect but probably a longer effect, however how would this longer change, effect us humans in the short term and long term
Reply | Report Abuse | Link to thisI’m sending a brief news release regarding Earth's magnetic field that you can use on your blog. You may take more information from the website if you like. Please consider using it. You can also find images on my website.
Reply | Report Abuse | Link to thisDennis
---------------------------------------------------------------
FOR IMMEDIATE RELEASE
Earth’s Magnetic Field Is Produced By An External Dynamo System.
Earth’s magnetic field is not produced by an internal dynamo within the planet as the conventional suggest. By Dennis Brooks, Image By NASA
New Theory: (Website Excerpt) Earth’s magnetic field is not produced by an internal dynamo. The magnetic field and the planet are parts of a complex dynamo system surrounding the planet. The system includes the planet, the magnetic field, radiation belts, and ring current. The same is true of the other planets. Saturn, Jupiter, Neptune, and Uranus are visible components of otherwise invisible planetary dynamo systems, which are all housed within a magnetosphere. According to this new theory, there is no internal dynamo within the outer core of the planet. Planet Earth does not have a unique way of producing its magnetic field. Nor do the other planets. Each magnetic field of each planet is produced in exactly the same way, by its planetary dynamo system. Visit the researcher’s website to read more.
http://sites.google.com/site/earthsmagneticfield/
Contact: Dennis Brooks
Email: dennisbroo@gmail.com
The flap about 12/21/2012 certainly has the world's attention.
Reply | Report Abuse | Link to thisWill it be a cataclysm, or simply the beginning of a new spiritual age? We'll just have to wait and see. Meantime, many credible scientific theories have been offered, including the possibility of a magnetic polar shift.
Could we survive it if we can foresee it?