The Mountains of Saint Francis : Discovering the Geologic Events That Shaped Our Earth

Modern geologists, Walter Alvarez among them, showed in the last decades of the twentieth century that the history of our planet has witnessed events profoundly more dramatic than even the most spectacular chapters in human history. More violent than wars, more life altering than revolutions—understanding the geologic events that have shaped the Earth's surface is the quest and the passion of geologists. In the knowledgeable and graceful prose of Alvarez, general readers are led to explore the many mysteries that our planet guards. The author has chosen Italy as a microcosm in which to explore this amazing past for several reasons. First, it is the land where the earliest geologists learned how to read the history of the Earth, written in nature’s rock archives. Second, it is where Alvarez and his Italian geological friends have continued to decipher the rock record, uncovering more historical episodes from the Earth’s past. And third, the lovely land of Italy is unusually rich in geological treasures and offers examples of the key processes that have created the landscapes of the entire world. The Mountains of Saint Francis begins in Rome. We discover that the landscape of Rome was built by violent volcanic eruptions in the very recent past, almost certainly witnessed by our human ancestors. Next we travel to Siena and come face to face with a fundamental discovery of the geologists—that much of the dry land that we currently inhabit was once underwater, beneath ancient seas or oceans. Then we stop in the small medieval city of Gubbio and contemplate the amazing secret that the limestone rocks kept hidden for 65 million years—that a huge asteroid smashed into the Earth, disrupting the environment so severely that the dinosaurs, and perhaps half of the other forms of life inhabiting the Earth at the time, disappeared forever, opening the way for the rise of the mammals and eventually of humans. The impact theory that came from those Italian limestones at Gubbio was