No. 59: Sep-Oct 1988
Asteroids and comets are being blamed these days for more and more of our planet's catastrophism -- biological, meteorological, and geological. What a turnabout in scientific thinking in just a decade.
F.T. Kyte et al have now provided additional details on meteoritic debris they first described in 1981. On the floor of the southeast Pacific, about 1400 kilometers west of Cape Horn, about 5 kilometers down, they found high concentrations of iridium in Upper Pliocene sediments about 2.3 million years old. Since the proposed projectile hit in very deep water, no crater was dug out. What did survive is called an "impact melt." This is debris rich in noble metals, such as iridium, and contains particles typical of a low-metal mesosiderite. Some 600 kilometers of the ocean floor received this debris. Kyte and his associates estimate the size of the impacting object at at least 0.5 kilometers in diameter.
No biological extinctions are correlated with the 2.3-million-year date, but there appears to have been a major deterioration of climate at about this time. There was a shift in the marine oxygen isotope records and, more obvious, the creation of the huge loess (sandy) deposits in China. What the impact may have done is to vaporize enough water into the atmosphere to increase the earth's albedo, reflecting sunlight back into space, lowering the average temperature, and thus triggering the Ice Ages.
(Kyte, Frant T., et al; "New Evidence on the Size and Possible Effects of a Late Pliocene Oceanic Asteroid Impact," Science, 241:63, 1988.)
Comment. Aficionados of the Ice Age problems will have to add this theory to the already long list of Ice Age hypotheses.