A simultaneously enlightening and cautionary tale of the deep history of our planet and the possible future, when conscious life may become extinct.
“Animal life has been almost entirely wiped out in sudden planet-wide exterminations five times in Earth’s history,” writes Brannen, who notes later, “life on Earth is resilient, but not infinitely so.” An extinction event is defined as “any event in which more than half of the earth’s species go extinct in fewer than a million years.” The author provides an overview of the five major extinction events that have occurred over the last 300 million years, evidence of which are revealed by the fossil record and appear to be correlated with major geological shifts. The most recent event, the extinction of dinosaurs, provides a case in point. The dominant form of life on Earth for more than 200 million years, they were likely felled by two major catastrophes that occurred around 66 million years ago: “the largest asteroid known to have hit any planet in the solar system…hit Earth…[and] one of the largest volcanic eruptions ever smothered parts of India in lava more than 2 miles deep.” Improbably, our planet has survived each of the five major extinctions. Fossils recovered in Ohio give evidence of what appears to have been the first mass extinction, around 450 million years ago, when “a vast tropical sea covered most of present-day North America.” Why this occurred is debatable, but it appears to have been associated with a rapid increase in the amount of carbon dioxide in the atmosphere, causing significant global warming. As the author warns, how we prepare for the possibility of a sixth major extinction event may be “existentially, even cosmologically, consequential.” Though not as in-depth on the future possibilities as some readers may want, the book is entertaining and informative on the geological record and the researchers who study it.
Brannen may not be Elizabeth Kolbert, but he provides a useful addition to the popular literature on climate change.