Wildfires: Apocalypse Then and Now
Weisburd, Stefi, Science News
Just when it was looking really bad for the dinosaurs, it got worse. Another element has been added to the already dire scene painted of the world 65 million years ago. Some scientists posit that is when an asteroid or torrent of coments pelted the plant, wiping out the dinosaurs and hordes of other life (SF: 6/2/79, p. 356). In addition to the possible dust clouds, blast waves, tidal waves and poisonous gases triggered by the impact, researchers at the University of Chicago have added yet another deadly plague: continent-size wildfires churning out massive clouds of soot that engulfed the globe
Their findings not only enhance understanding of the forces that drove the dinosaurs to extinction, but they provide a much needed quantitative basis for studies of future cataclysms that could befall the earth. In particular, "these data suggest that some of the assumptions used in nuclear winter scenarios were too optimistic,"warn the U. of Chicago's Edward Anders, Roy S. Lewis and Wendy S. Wolbach in the Oct. 11 SCIENCE.
Since high levels of iridium, normally rare in the earth's crust, were discovered in the "K-T" layer marking the geologic boundary between the Cretaceous and Tertiary periods, scientists have been exploring the possibility that the iridium came from a meteorite or comet shower. In order to determine what kind of asteroid might have struck the earth, Anders's group set out to analyze the noble (inert) gas content of clay layer samples, because the ratios of these gases provide a distinctive signature of their origin. One step in this process is to chemically isolate carbon from the clay layer since meteoric noble gases tend to be concentrated in such carbon residues.
But after the chemical etching, the researchers noticed that they were left with an unusually large amount of carbon. The concentration of elemental carbon in the residue was 4 to 5 times higher than that contained in rocks above and below the K-T boundary and it was 4 to 25 times greater than that found in modern marine sediments. Scanning electron microscopy of the samples revealed what the researchers think is soot -- small carbon particles made in irregular and fluffy shapes and sometimes formed in chain-like clusters. According to Anders these shapes and configurations are known to arise only from forest fires or the burning of fossil fuel. The researchers believe that the combusted organic matter came from living plants and animals and not fossil material at the impact site or from the asteroid itself; the asteroid, they explain, would have supplied oxygen for binding up the carbon atoms instead of the carbons linking themselves to form soot. Anders says that this conclusion is supported by the isotopic analysis of the carbon samples done recently by two British researchers.
The scientists suspect that wildfires could have been ignited by the heat from a fireball and a cloud of hot rock particles generated by the impact. Even if the asteroid had fallen into an ocean, as many scientists presume, it could have triggered fires on a continent thousands of kilometers away. …