No. 53: Sep-Oct 1987
"Nuclear winter" is a term now in vogue. And, believe it or not, the rains of tektites discussed below may have been the forerunners of climatic catastrophes similar to the postulated nuclear winters. We shall call them "meteor-impact winters.
First, a tad of background: Great meteor impacts and tektite events seem to have occurred nearly simultaneously with deep-cutting biological extinctions and reversals of the earth's magnetic field. Ever since this apparent synchrony was recognized a few decades ago, theorists have been vying in generating scientific scenarios, especially some mechanism that would reverse the earth's magnetic field.
New entrants in the lists are R. Muller and D. Morris, two Berkeley physicists. Here is how they see it:
"A sufficiently large asteroid or cometary nucleus hitting the Earth lofts enough dust to set off something like a 'nuclear winter.' The cold persists long after the dust settles because of the increased reflectivity of the snow-covered continents. In the course of a few centuries, enough equatorial ocean water is transported to the polar ice caps to drop the sea level about 10 meters and thus reduce the moment of inertia of the solid outer reaches of the Earth (crust and mantle) by a part in a million. 'That doesn't sound like much, Morris told us. 'But when we realized that this translates into a full radian of slippage between mantle and core in just 500 years, we began to look seriously at the consequences.' With the moment of inertia of the crust and mantle 'suddenly' decreased, the argument goes, they begin spinning faster than the solid-iron inner core at the center of the Earth. The 2300-km thick shell of liquid outer core that separates the mantle from the inner core thus acquires a velocity shear, which in the course of about a thousand years destroys the pattern of convective flows that served as the dynamo maintaining the Earth's dipole field."
The field reversal is not immediate according to both calculations and analyses of sediments. After the impact event, the dipole field decreases for a few thousand years, followed by a longer hiatus. Then, there is a sudden reversal. (Schwartzschild, Bertram; "Do Asteroid Impacts Trigger Geomagnetic Reversals?" Physics Today, 40:17, February 1987.)
Comment. In trying to relate all this to our present situation, recall that a major "ice age" is just a few millenia behind us, and our dipole field has been decreasing slowly for as long as we have been able to measure it. Brace yourselves!
Reference. There are many anomalies associated with the tektites. See ESM3 in our catalog: Neglected Geological Anomalies. Ordering information here.