In my latter days of graduate school (early 1963) at the University of Washington, the Oceanography Department featured visiting speaker Robert S. Dietz. He gave a very interesting talk on "sea floor spreading," a hot topic in marine circles at that time. Someone scrawled a small, informal notice on the Geology Department hall blackboard. It simply stated "Astroblemes," gave a room and time and there was the Dietz name again. What was an astrobleme? I asked around but nobody knew. It wasn't in the geological dictionary. I was curious. (For anyone who might not know, an "astrobleme" was Dietz's name for an ancient, obscure asteroid impact scar.) I went to the talk along with about 50 other people.

            Dietz gave a splendid talk. I was mesmerized from the first slide. He talked about Lunar craters and their origin. It was fascinating. He talked about Meteor Crater and the controversies regarding it's origin and showed why the impact origin was the correct interpretation. He pointed out that Lunar craters were gargantuan relative to Meteor Crater and raised the question of such large craters on the Earth. He then talked about the degredation of earthly craters to "fossil craters" and eventually "astroblemes." He pointed out that astroblemes could be recognized by such secondary features as "shatter cones" and the ultra-high-pressure mineral coesite. Every step of Dietz's discourse was clear, logical and well illustrated. Any scientifically literate person with a little geology background could have understood him.

            Once the audience agreed with his logic, he proceeded to illustrate bigger and bigger astroblemes. The last ten minutes of his talk were devoted to the Sudbury Structure, one of the most highly studied, most controversial geological localities on Earth. Dietz proceeded to interpret Sudbury as an astrobleme deformed into an oval shape by the Grenville Orogeny. The audience stiffened as he forced this interpretation down their collective throat. When the lights went on, the applause was sparse and pandamonium broke loose. The question period was somewhat rude and unruly. The decibel level was well above normal. One fellow stood up and loudly stated that he'd completed his dissertation on Sudbury and that Dietz didn't know even the first thing about basic field geology. For two to three days afterward, people were still grumbling and talking about Dietz being a nut.

            What a splendid talk! It still ranks as one of the best I've ever heard. A year later, Dietz published his thoughts ("Sudbury Structure as an Astrobleme:" Jour. Geology, v. 72, p. 412-434, 1964). It's now a classic. Check it out and enjoy it.

            In the Spring of 1963, I finished my dissertation and took a teaching position with San Diego State. Unbeknownst to me, Robert Dietz was employed at the Naval Electronics Laboratory in the Point Loma District of San Diego. John Holden and Nathan Ayer were two of his assistants and also were graduate students in our department. The three of us immediately shared intense interests and long involved discussions of impact structures, astroblemes and speculations regarding the Moon and other planets got under way. John and Nate greatly aided my understanding of the Earth as a planet. Remember, this was in the days prior to plate tectonics and virtually no geologists were thinking along planetary lines. But I remember when the first Mariner flyby images returned and showed Mars to be cratered like the Moon, we all knew that was what would be found. Everyone else was surprised.

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