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Science Frontiers ONLINE No. 52: Jul-Aug 1987 |
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Complexities Of The Inner Earth
So many new and startling facts about the inner earth are emerging from current magnetic, seismic, and gravitic researth that a little list is in order. Bear in mind when going down the list that most of these features would have been considered absurd only a decade or two ago.
- The earth's solid inner core, which "floats" inside the liquid core, is not spherical. Rather, it is anisotropic with its axis of symmetry aligned with the earth's axis of rotation. (Ref. 1 below)
- "The CMB (core-mantle boundary) is the most dramatic discontinuity in the earth's internal structure in terms of the physical and chemical properties as well as the time scale of the processes that take place on either side of it. Its shape, if different from that predicted by the hydrostatic equilibrium theory, may contain information important to our understanding of geodynamic processes in the mantle or the geomagnetic field generated in the outer core." (Ref. 1, and also item #7 below)
- The earth's magnetic field possesses four lobes which remain fixed relative to the earth's surface, as demonstrated by 300 years of data. These lobes do not drift westward like the general field. (Ref. 2)
- "Core-spot pairs" of magnetic intensity seem to move westward and poleward. In the southern hemisphere, they originate under the Indian Ocean and drift under South Africa into the southern Atlantic. This motion reminds one of sunspot motion, except that sun-spots move equatorward. There may be a connection here. (Ref. 2)
- The general decrease in the earth's magnetic field over the past few centuries may be due to intensifying core spots, which are magnetized in a sense opposite that of the main field. (Ref. 2)
- Large, deep earthquakes in 1983 and 1984 produced slow, wavelike
changes in the local gravitational field at the surface, as measured by new superconducting gravity meters. The periods were 13-15 hours. (Ref. 2)
- Gravity and magnetism measurements from satellites show strong, coincident anomalies in the Indian Ocean (3�N 81�E). In fact the whole ocean surface is depressed in this region. To explain these overlapping anomalies, geophysicists suggest that a "valley" 5-10 kilometers deep exists at the coremantle boundary. (Ref. 3)
References
Ref. 1. Dziewonski, Adam M., and Woodhouse, John H.; "Global Images of the Earth's Interior," Science, 236:37, 1987.
Ref. 2. Weisburd, Stefi; "The Inner Earth Is Coming Out," Science News, 131:222, 1987.
Ref. 3. "Satellites See Valleys in the Earth's Core," New Scientist, p. 33, May 21, 1987.
Comment. Reviewing Item 5 above, one wonders if the so-called "core spots" might attain such strengths that they locally reverse the terrestrial magnetic field at the surface. If so, geological scenarios relying on paleomagnetism (like continental drifting) would become suspect.