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Science Frontiers ONLINE No. 80: Mar-Apr 1992 |
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The Steens Mountain Conundrum
The layered lava flows of Steens Mountain, in southeastern Oregon, have preserved video-like records of the earth's magnetic field as it switched from one polarity to another about 15.5 million years ago. The scientific "instruments" here are the cooling lava flows. As they solidify from the outside in, a process taking about 2 weeks for a 2meter-thick flow, the lava is magnetized in the direction of the field prevailing at the moment of solidification. We would thus have a 2-week continuous record of the behavior of the earth's field. Ordinarily, we would not expect to see very much change in 2 weeks; even a reversing field is thought to take thousands of years to complete its flip-flop. However, at Steens Mountain, when the field reversed 15.5 million years ago, the lava flows suggest that the field's axis was rotating 3-8� per day -- incredibly fast according to current thinking, in fact a thousand times faster than expected.
The conundrum (one might call it a scientific impasse) arises because the flowing electrically conducting fluids that supposedly constitute the earth's dynamo would have to flow at speeds of several kilometers/hour. No one has ever contemplated molten rock moving at such speeds in the core!
(Appenzeller, Tim; "A Conundrum at Steens Mountain," Science, 255:31, 1992. Lewin, Roger; "Earth's Field Flips Flipping Fast," New Scientist, p. 26, January 25, 1992.)
Could it be that the prevailing dynamo theory is incorrect?
To make matters more interesting, it now seems that the paths taken by the reversing poles follow similar routes with each flip-flop. One preferred path is a band about 60� wide running northsouth through the Americas; the other path is 180� away cutting through east Asia and just west of Australia. The implication is that some unknown structure in the core somehow guides the reversing poles.
(Anonymous; "A New Path to Magnetic Reversals," Eos, 72:538, 1991.)
Reference. Additional doubts about the dynamo paradigm are expressed in EZF3 in our catalog: Inner Earth. For further information, visit: here.