The Mountains of St. Francis

by Walter Alvarez

Walter Alvarez has devoted his career to study the Apennine mountains of Italy. Most of this work is hard, slow, slogging accumulation of data and laboratory experiments. However, in the early 1980s, while studying a particular kind of limestone there, he came across an abrupt discontinuity in the rock strata. A thick layer of limestone lay atop a very different kind of limestone. Between the two limestone layers was a very thin layer of something else. Alvarez had it analyzed, and discovered that it contained extraordinarily high amounts of iridium. There is no geological mechanism that could have concentrated iridium in such a layer -- but meteorites contain such high amounts of iridium. This solved the debate regarding the sudden end of the dinosaurs 65 million years ago: a huge meteorite hit the Yucatan peninsula, kicking up so much atmospheric life that many species died.

Although this is the discovery for which Alvarez is most famous, it was serendipitous: the bulk of Mr. Alvarez’s work has been the reconstruction of the geological history of Italy. And a strange history it is. Italy is a platelet: a small chunk of crust too small to be considered a plate. For much of earth’s history, that platelet was part of the African plate, but for complicated reasons the Italian platelet broke free from the African plate and moved northward. The European plate was still far away, and for millions of years, much of the Italian platelet lay deep underneath the ocean, collecting bits of dead sea plankton as it drifted downward. At some point it began to move in a northeasterly direction, and things get complicated. The cause of this motion is too complicated for me to attempt to explain, and I’m not sure that I understand it. But it pushed the Italian platelet northeastward and simultaneously shoved it upward; this upward movement created the Apennines. In the process, all sorts of geological mayhem took place: entire chunks of crust were flipped over and deposited on top of younger rocks. Of course, this took place over millions of years; there was nothing that might interest Hollywood.

Soon after, the Italian platelet crashed into the European plate, raising the Alps. In a complicated motion, Corsica and Sardinia rotated toward the southeast; this triggered volcanic activity, first in the area of Rome, then moving south to Naples and now Sicily. The Seven Hills of Rome are actually ancient volcanoes that have been eroded almost completely away. Anyway, that’s the process as I understand it.

Alvarez’ goal for this book, I think, was to summarize his life’s work. He threw in plenty of charming anecdotes about the Italian countryside and the fellow geologists whom he befriended. But I think he failed in his goal of teaching the popular reader about the geological history of Italy, or the significance of his work. It starts off easily enough with a simple discussion of the geology around Rome, but the deeper he gets into the story, the harder it is to follow. I’ve read a lot of geology, and I started losing track of the story about two-thirds of the way through. I think that the problem arises from his attempt to mix three very different stories: his personal experiences in Italy, the discoveries that led to the scientific conclusions, and the final geological history that we have for Italy. By interweaving them, Alvarez makes it harder to keep track of each. That’s not a problem with the first two stories, but the third story is so complicated that it deserves special treatment. I think he should have added an appendix tracing the history in a series of maps showing how he thinks Italy got to its current location and structure. This would have made the text much easier to follow.