A Most Improbable Journey: A Big History of Our Planet and Ourselves by Walter Alvarez, and: The Little Book of Big History: The Story of Life, the Universe and Everything by Ian Crofton and Jeremy Black (review)

These two concise books address big history in different ways, showing that history even at the largest scale can be told in many ways. Though their differences are many, the contradictions between the two are few. The Alvarez book focuses on a geological approach to big history, told through personal narratives of his encounter with the evidence. Crofton and Black adopt what could be called a human-society approach to big history, working political and social history into the big history focus to the degree possible. Each draws a line between the human era and the time before: for Alvarez about 75 percent of the book addresses the pre-human era; for Crofton and Black a much smaller 25 percent of the book is on the pre-human era.

Alvarez is known as the geologist who articulated the thesis that a giant meteor hit Yucatan and caused the species extinction 66 million years ago, eliminating the dinosaurs. Using the first person, he leads readers with a personal touch, telling tales about the researchers in explaining scientific discoveries of the cosmos and earth and even the era of humans. His first chapter ends with a brief grounding in today's "human situation."

The book then turns to an elegant summary of the creation of the universe and the unfolding of the earth's geology. It emphasizes that the earth was unusual among the solar planets in that heavy elements—oxygen, magnesium, silicon, and iron, became most plentiful. Alvarez describes the slow processes of sorting and concentration of these elements, focusing on silicon because of its importance in tools, glass, and computers. In the first case, a biological process helped to create rock: silicon dioxide, extracted by oceanic sponges from seawater, was eventually precipitated to create chert, a form of hard rock that was essential in creating early stone tools. In the second case, plate tectonics created silica in sand and sandstone. As expanding oceanic crust was forced under continental plates, molten rock emerged in volcanoes. The last elements of the molten rock to solidfy were almost pure silicon dioxide, forming quartz, a major component of granite. As the volcanic mountains were weathered, granite was worn down into tiny chunks of quartz which became cemented together as sandstone—the raw material for making glass during the past 5,000 years and silica for computers today.

Alvarez shows geological dimensions of the evolution of life—for instance that photosynthesizing microbes emitted waste oxygen into the atmosphere, thereby poisoning many of the early archaea and eubacteria, and laying the groundwork for eukaryotes. For this third type of life, with both nuclear and mitochondrial DNA, most species relied on oxygen for survival. Of the four kingdoms of eukaryotes, Alvarez selects the animal kingdom and traces the stages of animal evolution—the time frame and the logic—from tube worms to bilateral symmetry, to tetrapods, the dominance of dinosaurs, and the expansion of tiny but warm-blooded mammals to fill many ecological gaps once dinosaurs had gone.

His analysis of human society focuses mainly on material issues. He follows up the long coevolution of fire, plants, and animals with stories of human control of fire for cooking and, later, for pottery, glass, and metals. He provides a handy hint for comparing and linking the passage of time in geology and in human society: humans have had writing for 5,000 years, while the age of the earth is 5,000 million years, so that this million-to-one comparison enables us to keep both in mind.

Alvarez ends his narrative with the Bronze Age and...