Claim CD741:
Plate tectonics became widely accepted when bands of reversed magnetic
orientation were found mirrored on either side of the Mid-Atlantic Ridge.
According to the theory, the sea floor spread gradually from the
Mid-Atlantic Ridge, and periodic flips in the earth's magnetic field were
preserved and recorded in the rocks as emerging magma cooled.
But these bands of magnetism were misinterpreted; there are no magnetic
reversals. Although magnetic intensities fluctuate, these are slight
deviations around a high average. A compass needle would not change
direction over these bands.
Source:
Response:
- The magnetic field preserved in the rocks themselves does change
direction. The magnetism measured in the 1950s was measured at the
ocean surface, so the earth's present magnetic field was added to the
magnetism from the rocks below (Bishop 1981).
- The main significance of the data was that the pattern was mirrored on
either side of the midocean ridge. This is just the pattern one would
expect from sea-floor spreading.
- There is a great deal more evidence for plate
tectonics.
References:
- Bishop, A. C., 1981. The development of the concept of continental
drift. In The Evolving Earth, ed. L. R. M. Cocks, London: British
Museum, pp. 155-164.
created 2004-2-13
