THE STORY OF THE EARTH IN 25 ROCKS

A natural follow-up to the author’s The Story of Life in 25 Fossils (2015).

In many of the chapters, paleontologist and geologist Prothero doesn’t necessarily discuss specific rocks but rather larger geological phenomena. The result is a rewarding, surprisingly detailed education on the history and present state of earth science. The author begins with the eruption of Mount Vesuvius, which “can be considered the beginning of our modern understanding of Earth and the event that led to the birth of geology as a science.” Meteorites reveal so much that they deserve two separate chapters. Most are rocky material that turn out to be exactly 4.5 billion years old, which is the age of the planets, and scientists agree that these consist mostly of material like asteroids and comets that never coalesced into larger bodies. About 5 percent of meteorites are mostly solid iron. The core of the Earth is also mostly iron, so these are the remaining bits that didn’t sink deep into the planets when they were still molten. Ancient plants died, piled up, and became coal because insects and microorganisms that digest dead vegetation hadn’t evolved. No more coal is being formed. Iron in ancient oceans precipitated into massive iron mountains that industry depends upon. Oxygen converts iron into useless iron oxide (rust), but ancient oceans had no oxygen. It does today, so no iron mountains are being formed. In some chapters, the author examines the life and career of a geological genius—Louis Agassiz (1807-1873) proposed that the Earth had undergone ice ages and eventually convinced his colleagues. In “Jigsaw Puzzle Bedrock,” Prothero introduces Alfred Wegener (1880-1930), who spent his life proposing that the continents were once joined and are now drifting apart. Almost no one believed him until long after his death.

An occasionally scattershot but agreeable, useful introduction to geology.