Tony Hegg Stephanie Irish October 28, 2005

1. Tony Hegg Stephanie Irish October 28, 2005 GEOMAGNETISM

2. Outline • Basic Magnetism • Earth’s Magnetic Field • Origin • Main Field • Magnetic Poles • Magnetosphere • Aurora Borealis and • Geomagnetism of the Past and Present • Paleomagnetism • Current Geomagnetic field • Geomagnetism of the Future: Field Reversal • The Argument For • South Atlantic Anomaly • Movement of the Poles • Weakening of the Field • The Argument Against • Effects of a Possible Reversal • Conclusion

3. Basic Magnetism • Magnetism is a long-range force. • A magnet is a dipole, with North and South orientation. • A magnetic field is created by a magnet, much like the electric field. Lines originate at the north pole and terminate at the south pole. • Magnetism is related to electricity and current because moving charges are the source of magnetic fields.

4. Magnetism of Matter • Electrons have a magnetic moment that is called electron spin. In an atom, these spins oppose each other. A full shell has a net magnetic moment of zero, but an atom with an odd number of electrons results in an unpaired spin and a net magnetic moment. • In most elements, the atoms with magnetic moments are randomly arranged, producing a solid with a net magnetic moment very close to zero. However, there are certain elements in which the atomic magnetic moments align due to spin interactions. These elements, the most prominent being iron, have the properties of a magnet and create their own magnetic field.

5. Curie Point When a ferromagnetic solid reaches or exceeds the Curie Temperature (1043 K for iron) magnetic ordering is destroyed. Earth’s outer core, where the magnetic field is formed, reaches temperatures around 6000 K, creating the need for an alternate explanation for the formation of the Earth’s magnetic field.

6. Dynamo Theory • Theory that the Earth’s Magnetic Field is created continuously within the core. • Rotation of the Earth causes a similar, though not simultaneous, rotation in the conducting, liquid metal core which flows across the existing magnetic field. Electric currents are induced, creating a second magnetic field. This second magnetic field reinforces the first and a dynamo is created which sustains itself.

7. Magnetic Elements To measure the direction and intensity of the field, there are seven parameters that are used: • Declination (D) • Inclination (I) • Horizontal Intensity (H)- Intensity in the xy-plane 4. North component (X) 5. East component (Y) • Vertical Intensity (Z)- Intensity in the z direction • Total Intensity (F)- magnitude of the intensity

8. Main Field • Although the Earth’s Magnetic Field is often represented as a bar magnet, it is much more complicated than that. • The main field includes the field at the surface of the Earth, magnetic poles, and the magnetosphere.

9. Magnetic Poles There are two magnetic poles that are created by the geo-dynamo in the core. These poles are like the poles of a bar magnet, but more complicated. Because the poles are created by electric current in a shifting liquid core, the poles are not stationary and not necessarily 180 degrees apart.

10. Magnetosphere The Earth’s magnetosphere extends tens of thousands of kilometers into space. It is comprised of the Van Allen Belts, magnetopause, and the magnetotail.

12. The Auroras • The auroras experienced near the poles of the Earth are a direct result of the Earth’s Magnetic Field.

13. Paleomagnetism • Paleomagnetism is the study of geomagnetism of throughout the epochs of time by examining polarization. • Primary magnetization is the polarization during the formation of rocks and must be distinguished from secondary magnetization (polarization after formation). • By examining this magnetization, scientists can determine the properties of Earth’s magnetic during different periods of history.

14. Application The study of Paleomagnetism is useful when looking at the history of field reversals. During a period of reversed polarity, the rocks that form will be polarized in the opposite direction as those that form under normal polarity.

15. Current Magnetic Field At the present time, the Magnetic Field is weakening and the poles are “rapidly” shifting. Could it be a reversal?

16. Reversal Facts • Magnetic field reversal occurs approximately once every 250,000 years. I has currently been 780,000 years since the last known reversal (the Brunhes-Matuyama reversal). • While scientists are unsure what causes reversals, there are two main theories about what might happen. • The core becomes quasi-stable, causing the poles to migrate and reorient • The dynamo is disrupted by an outside force causing the field to “shut off.”

17. The Future of the Field Many scientists are predicting that a reversal of the Earth’s Magnetic Field is already in progress. One model of past and imminent future reversals is the Glatzmaier-Roberts computer model, shown here: http://www.pbs.org/wgbh/nova/magnetic/reversals.html

18. South Atlantic Anomaly In the South Atlantic, there is a spot where the magnetic field strength dips, causing the radiation in the Van Allen belts to come very close to Earth’s atmosphere.

19. Movement of the Poles This is a map of the location of the north magnetic pole from 1600 to 2001. This movement, as well as that of the south pole, is due to shift in the magnetic field in the core of the Earth

20. Weakening of the field The intensity of Earth’s Magnetic Field is currently diminishing at an accelerating rate rate. The weakening began 150 years ago, with a total decrease of 10-15% from then to the present. If this deterioration continues at the present rate, the field will disappear in 1000-2000 years.

21. Proof of a Reversal? While the magnetic field is decaying, the changes are well within the normal fluctuation of the field (coinciding with the movement of the liquid core) and its geomagnetic excursions. The movement of the poles is an ever present and ongoing phenomenon.

22. Effects of Reversal • knock out power grids • harm satellites orbiting Earth (already occurring) • widen holes in ozone layer • create auroras at the equator • disrupt the migratory patterns of fish, birds, and marine life that rely on the magnetic field for navigation.

23. Dynamo Death The moon is slowing down the rotation of the Earth. This rotation is essential in maintaining the dynamo, and therefore the magnetic field.

24. Bibliography • “Earth’s Magnetic Field.” Wikipedia. <http://en.wikipedia.org/wiki/Geomagnetism> • “South Atlantic Anomaly.” Wikipedia. <http://en.wikipedia.org/wiki/South_Atlantic_Magnetic_Anomaly> • “Dynamo Theory.” Wikipedia. <http://en.wikipedia.org/wiki/Dynamo_theory> • “Magnetosphere.” Wikipedia. <http://en.wikipedia.org/wiki/Magnetosphere> • “Geomagnetic Reversal.” Wikipedia. <http://en.wikipedia.org/wiki/Geomagnetic_reversal> • “Geomagnetism: North Magnetic Pole.” Geological Survey of Canada. <http://gsc.nrcan.gc.ca/geomag/nmp/northpole_e.php> • “Poles.” Australian Antarctic Division. <http://www.aad.gov.au/default.asp?casid=1843> • “Magnetic Storm.” PBS NOVA. <http://www.pbs.org/wgbh/nova/magnetic/> • “ Will Compasses Point South?” New York Times. <http://www.nytimes.com/2004/07/13/science/13magn.html?ex=1247457600&en=e8f37e14d213ba16&ei=5090&partner=rssuserland> • National Geophysical Data Center (NOAA Satellite and Information Service). <http://www.ngdc.noaa.gov/seg/geomag/faqgeom.shtml> • Merrill, Ronald T., Michael W. McElhinny, and Phillip L. McFadden. The Magnetic Field of Earth. San Diego: Academic Press, Inc., 1996. • Campbell, Wallace H. Introduction to Geomagnetic Fields. New York: Cambridge University Press, 1997. • Sharma, A. Surjalal, Yohsuke Kamide, Gurbax S. Lakhina, Ed. Disturbances in Geospace. Washington D.C.: American Geophysical Union, 2003. • Chaisson, Eric. Astronomy: A Beginner’s Guide to the Universe. Upper Saddle River, NJ: Pearson Education, Inc., 2004. • Knight, Randall D. Physics for Scientists and Engineers. San Francisco: Pearson Education, Inc., 2004.

25. Abstract: Geomagnetism The magnetic field is a complex part of Earth. While an understanding of the basics of magnetism is essential, the temperatures at the core of the Earth where the field originates require scientists to look beyond ferromagnetic properties and bar magnets for the field’s origin. The leading theory for the creation of Earth’s magnetic field is the Dynamo theory. The Dynamo leads to the formation of the main field, consisting of magnetosphere, Van Allen belts, and the magnetopause. An interesting consequence of the Dynamo is the reversal of the entire field. Past reversals are observed through the used of Paleomagnetism, the examination of the magnetic field of rocks in different layers of the Earth’s crust. These observations, along with the current conditions of our magnetic field, have lead some scientists to hypothesize that presently Earth is entering a period of magnetic reversal. Currently, the poles are drifting rapidly and the field is steadily weakening. The South Atlantic Anomaly also provides support for reversal. If a reversal was to occur, harmful ionized particles from the Sun would enter Earth’s atmosphere, with varying consequences. However, there is some debate over whether or not a reversal is in progress. The changes in the field are within the expected limit and are simply due to the random flow of the Dynamo. Finally, the Moon will have an adverse affect on Earth’s magnetic field over time. It is clear that geomagnetism is a very dynamic and complex topic that includes much theory and debate about its past, present, and future.