Rare Earth by Ward and Brownlee
Rare Earth: Why Complex Life Is Uncommon In The Universe
by Peter D. Ward & Donald Brownlee
A few years ago a book that looked interesting by these two men – The Life And Death Of Planet Earth – turned out to be fantastic, and inspirational for me. So when I spotted a second work by the pair I had to read it.
This second book details what the authors call the Rare Earth Hypothesis, which in a nutshell states that simple life – prokaryotic life and perhaps eukaryotic single-celled life – is common, but that multicellular, and particularly animal life is rare. The authors stake out their territory by describing the likely evolution of habitable zones in the universe, the creation of Earth and the solar system, and then the evolution of life. As many have observed, life appeared on our planet just about as early as was possible, which strongly suggests that the basic biochemical reactions (recently outlined by the brilliant Nick Lane in his tour-de-force The Vital Question) are comparatively simple, and even likely – for instance in hydrothermal vents at the ocean floor. Sections follow on the appearance of multicellular life, Snowball Earth, and then a crucial section on the Cambrian Explosion. Mass extinctions are covered, and then a vital section on plate tectonics.
Further chapters deal with the crucial importance of Jupiter and its position in the solar system, and the Moon, before the end chapters of the book deal with tests for the hypothesis and an assessment of the odds.
Some reviewers of this book, written in 2000, have in my opinion been unfair when calling it inconclusive. The authors themselves point out more than once that they are writing at a time of great change in extra-solar astronomy; and we only have to think of the extraordinary discoveries made in the last decade to realise that these authors were courageous in putting forward their hypothesis. In my opinion they were notably far-sighted too. Their book is a detailed statement of the Rare Earth hypothesis.
This book is a superbly written, thorough and fascinating look at the ultimate scientific question: how is life spread across the universe? We 21st century human are incredibly lucky that this question could be answered in our lifetimes. In the 2030s and ’40s a mission is likely to arrive either at Enceladus or Europa, sampling the components of those enigmatic satellites. If simple bacterial-type life exists on either of the satellites, the authors of this terrific book will have the first of their answers.