Prof. Dr. Gerald M. Friedman

CHAIR OF GEOLOGY AND GEOGRAPHY SECTION (SECTION E) AND COUNCIL DELEGATE OF AAAS, 1978-1980

An important innovation in my second edition of my sedimentology textbook (Friedman et al. 1992) was the chapter on extraterrestrial forcing functions, a new approach to the study of terrestrial sedimentary deposits. The following example illustrates why it was necessary to discuss extraterrestrial forcing functions. In 1978-1979, coinciding with the publication date of the previous textbook (Friedman and Sanders 1978), a symposium on extinctions in the fossil record was held. One of the speakers was physicist Nobel Laureate Louis Alvarez (1911-1988), who presented to an unbelieving and hostile audience of geologists his hypothesis that at the end of the Cretaceous Period an asteroid or comet struck the Earth at the end of the Cretaceous, with catastrophic effects. Hence, the extraterrestrial factors have become recognized as important processes affecting the formation of sedimentary deposits. In the 1978 book (Friedman and Sanders 1978), only a brief section in a complement to the main text explained the effects of the Moon and Sun on the mechanics of the tides. By contrast, in the 1992 edition an entire chapter was devoted to extraterrestrial forcing functions. Within it are such topics as planetary orbits, Milankovitch climatic factors, oceanic tides, and the Sun’s orbit.

The uniformitarian concept emphasizes the slow steady state: evolutionary processes of the kind that humans observe and experience on a daily basis. At the beginning of the 1980’s this emphasis shifted to catastrophic or convulsive events. I like to reminisce on this point from the vantage of personal experience. In 1978/1979 I became chairman of the Geology and Geography Section (Section E) of the American Association for the Advancement of Science (AAAS) and then became Council Delegate of AAAS. The assigned duty was to plan and organize symposia for the next annual convention.

Together with the other section delegates, section chairs and council delegates, we put together excellent symposia for the 1980 annual meeting to be held in San Francisco on 3-8 January. Curiously, at this meeting a program had sprung up that had not been planned and came as a complete surprise. This non-planned program centered on a Nobel laureate physics professor, and was not even listed in the AAAS 1980 program. The featured speaker was Louis W. Alvarez (1911-1988), professor of physics emeritus and associate director at large of the Lawrence Berkeley Laboratory, California. In the 1980 program, where I was listed as retiring chairperson of Section E-Geology and Geography, he was shown as a member of the “San Francisco Advisory Committee” and his function on the program as “Youth Symposium, Frontiers of Science, and Session Aides Subcommittee.” Yet the title of his paper was not in the formal program. It was inserted as a program change for Friday, 4th of January, on a separate piece of paper. The names of his three co-authors were not on the inserted program addition. They included his geologist son Walter Alvarez, and two analytical chemists. The chemists were specialists in the analyses of platinum and iridium.

Alvarez presented to an unbelieving audience that an asteroid of 104 kilometers diameter struck the Earth at the end of the Cretaceous and caused mass extinction. This bold proposition resulted from their discovery, near the medieval town of Gubbio, Italy, of a centimeter-thick clay layer among limestones that straddled the Cretaceous-Tertiary boundary. They found that the clay contained 6.3 ppb of iridium which compared with a crustal iridium abundance of less than 0.1 ppb. They surmised that extraterrestrial sources, namely an asteroid, produced the iridium anomaly. This unplanned presentation, together with its speculation, unnerved me. How much do we know about the distribution of iridium in the various lithologies of the Earth’s crust? The speaker did not reveal abundances, but dwelled on the difficulty of iridium analyses in which his chemist-coauthors were involved. I asked him that if extinction at the Cretaceous-Tertiary boundary was the result of an asteroid impact, then what had happened at the Permian/Triassic boundary, when extinction of life was more calamitous than at the Cretaceous/Tertiary boundary. Alvarez answered that as a physicist his thoughts were: if an impact had afflicted the Earth’s biosphere at the Cretaceous/Tertiary boundary, a similar event must have extinguished life at the end of the Permian.