Bruce Buffett presents a public talk at UC Berkeley on July 17, 2010, as part of the Science@Cal Lecture Series described at

Many of the planets in the solar system have internally generated magnetic fields. All of these fields are produced by the motion of an electrically conducting fluid in the interior, although the details vary from planet to planet. Historical observations of the magnetic field on Earth show that the field is continually changing on time scales as short as a few years. Earth's magnetic field also exhibits spontaneous polarity reversals, which cause the north and south magnetic poles to flip. The mechanism for reversals is not well understood, but geological records suggest that the onset of reversals is accompanied by a sudden reduction in the field strength. A strong field re-emerges from the interior as the new polarity is established. In this presentation I will discuss the origin of planetary magnetic fields. I will also speculate about the current decline in Earth's field, which has prompted some researchers to suggest that the field is entering the next reversal.

Bruce Buffett is a Professor of Geophysics in the Department of Earth & Planetary Science at the University of California, Berkeley. He received his PhD in Geophysics from Harvard University and was a Research Fellow at the University of Cambridge. He moved the University of California in 2008 after holding a faculty appointment at the University of Chicago.

Videography and editing by Chris Klein. This video is released under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 License -

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