LATE CRETACEOUS Helen Your assetation that the origin of the Earth's magnetic field is unknown was true when you and I were in grade school. However, science has demonstrated how it occurs and it is widely accepted among scientists. Have you ever heard of a little publication called Scientific American? http://www.sciam.com/askexpert/geology/geology9/geology9.html Jupiter's magnetic field (caused by flowing liquid metallic hydrogen) is so huge it even protects it's moons (Serious scientists even entertain the notion of Europa harboring life). The following brief excerpts from NOAA's "spaceweather.com" website reveal some of the story: AURORA BLAST: A fast-moving coronal mass ejection that billowed away from the Sun on Nov. 4th 2001 swept past our planet at 0150 UT on Nov 6th (8:50 p.m. EST on Nov 5th). The impact triggered a severe geomagnetic storm -- now subsiding -- and widespread auroras reaching as far south as Alabama and Texas in the United States. * * * RADIATION STORM: Our planet remains inside a stream of energetic solar protons accelerated by Sunday's X1-class solar flare and coronal mass ejection (CME). The ongoing radiation storm reached severe (S4) levels on Monday, but is subsiding now that the CME passed our planet. JOHN2001 As to some of the comments regarding the Earth's magnetic field and the mechanism which generates it, I would point readers to: http://www.igpp.lanl.gov/Geodynamo.html Recent computer modeling suggests the Earth's magnetic field is generated by convection currents within the Earth's fluid outer core (rather than the earth's rotation, as suggested by some posters) is the source of the Earth's magnetic field. LATE CRETACEOUS The Earth's rotation influences the fluid dymanics of liquid metals (mostly iron) in the outer core. If the Earth did not rotate the liquid would flow in a convection current. Rotation sets up a symmetry, roughtly aligned with the axis of rotation. This produces a spiralling flow orientated parallel to the axis. So, yes it is the flow of liquid metal which generates electricity and therefore a magnetic field (flowing electricity always has a magnetic field), but it is the rotation of the planet that creates the pattern and sets up planet wide polarity. Without rotation the magnetic field would not be so polarized. Get it? JOHN2001 Of course the rotation of the earth is *necessary* for the particular convection effects, but it is not a *sufficient* condition for the generation of the field. To say that A causes B implies that you are stating a necessary and sufficient condition, which, in this case, you are not. JOE MEERT Indeed! The generation, sustenance and reversal of the dipole field is one of the great mysteries of geoscience. There are a number of models for the generation of the main field (dynamos), but all of them are incomplete. If you want to look at a fairly up-to-date review of the many models, I suggest "The Magnetic field of the Earth" by Merrill, McElhinny and McFadden (1998). It gives a good overview of the many models. I can't find the reference right now, but there are a number of time-scaling problems with the recent supercomputer models. The importance of convection in the outer core and differential rotation of the inner/outer core for generating the main field are not well constrained. HELEN Have you ever heard of a little publication called Scientific American? http://www.sciam.com/askexpert/geology/geology9/geology9.html[/b] Yes, LC, I've heard of it....vaguely....once or twice in my life..... I'm SURE I have....I even have a subscription somewhere around here…. The dynamo model is presumed. It is not KNOWN. There are some interesting models concerning it and the possible reasons for field reversal. But whether or not it is widely accepted is simply not the point. Truth is not truth because the majority votes that way. The dynamo model may be correct. I am not arguing that. What I am saying is that at this point it is simply not a known thing. That's not bad! It's only bad if someone states it IS known. It's a model that is being worked with. That's good, too. But not knowing something is not a slam against any kind of science. It simply means we are finite human beings and still discovering things. On the other hand, I could have saved all these words and simply pointed out the posts above!