To: The Climate Club — C759 From: Walt Roberts 9 March 1985 PROVOCATIONS -- #44 of the Dinosaurs: Volcanoes or Asteroid

Violent climatic events eradicated the dinosaurs at the close of the Cretaceous geologic period some 65 million years ago. Two plausible theories have emerged to explain what happened. The final verdict isn't in as to which is right, or even possibly whether both contributed.

The mass of life at the end of the Cretaceous are well documented in the records. Not only were the dinosaurs wiped out, but perhaps half of the shallow water invertebrate animals and many other sea creatures. On land the dinosaurs vanished, but most plants, fresh water organisms and small mammals survived.

Other geologic periods have also seen megadeath events. The Permian some 225 million years ago wiped out perhaps 90% of all shallow water invertebrates. Do the extinctions have a common cause? Older theories held that the causes were large climate shifts, or drying up of the sea, or the drastic uplift of mountain ranges. But it now seems more likely that the responsible mechanism was a cataclysm associated either with the impact on Earth of an asteroid from space or the outbreak of gigantic volcanoes. Either could fill the sky with dust so dense as to darken the earth for months, and produce a devastating cooling not unlike that of the "nuclear winter" that might follow large scale nuclear war. Any of these could eradicate vast numbers of living things.

Nuclear scientist Luis Alvarez, working with his geologist son Walter and other colleagues advanced a novel theory 1979. The earth, they surmised, was struck by a large asteroid, and in the ensuing explosion vast quantities of the element iridium were dispersed throughout the atmosphere, along with other dust and debris, making everywhere an iridium-rich layer of dust that has now sunk into the fossil rock records. Their reason for suggesting an extraterrestrial body is that iridium is scarcely detectable in normal rocks of the earth’s crust, but is common in meteorites that rain onto the earth from space. An asteroid is a space rock similar to meteorites, but far larger, and thus it could explain the dust layers rich in iridium that have been found all around the earth in rock layers laid down at the end of the Cretaceous.

The latest issue of "Science" supports another explanation— giant volcanoes. Charles Officer and Charles Drake, Dartmouth College experts in volcano research, point out that iridium is found in the earth's molten core, and that the recent Kilauea volcano in Hawaii released iridium in abundance 10,000 times that of ordinary non-volcanic rocks of Hawaii. They also indicate that there is ancient evidence for volcanoes more than 400 times the magnitude of Krakatoa in 1883, which produced darkness at noon for hundreds of miles downwind. An outbreak of such volcanic activity could have produced the death of the dinosaurs.

There are some signs that the Cretaceous ended with a huge, sudden cataclysmic event, but that there was also the sun-blocking dust spewed forth in a sequence of events over perhaps 10,000 to 100,000 years. Perhaps an asteroid impact was one cause, and it was followed by a series of super-volcanoes and these together did the damage.

The final answer is not yet known. Scientists don't like to find multiple causes for a single event, so there will still be lots of research to try to pin the death of the dinosaurs to the one or the other