Paul G. Falkowski. 2015. Life's Engines: How Microbes Made Earth Habitable. Princeton University Press, Princeton, NJ, U.S.A., ISBN 978–0–691–15537, 205 pp., $24.95. Microbes rule the land and sea, always have and always will. They were the first life forms on Earth, dating back nearly 4 billion years, and their presence changed the chemistry of the planet and allowed for the evolution of higher life forms, including humans. As Louis Pasteur stated more than a century ago, “The very great is achieved by the very small.” Ironically, microorganisms were among the last life forms to be discovered and many of their vital secrets have not yet been revealed to the scientific world. What is known about the hidden world of the microbes and their fundamental roles in sustaining planetary habitability is insightfully revealed by Paul Falkowski in this authoritative, comprehensive, and delightful book. The author is uniquely qualified, perhaps singularly so, to cover topics ranging over broad time and space scales with a scholarly, transdisciplinary perspective that ranges from fundamental physics and chemistry, to Earth and ocean sciences, to ecology and evolution. I cannot think of any other scientist who would accept such a challenge. Falkowski's new book is very engaging and leaves the reader not only with an important scientific framework of Earth's history but also with important questions that reach even beyond our current understanding into an unknown world that is ripe for further exploration and discovery. The writing style is unique and, for those fortunate enough to know the author, “classic Falko.” He is a gifted scientist and writer, and legendary storyteller. Falkowski's epic scientific journey through time begins in a New York City housing project at the edge of Harlem. While still in his first decade of life, and with the curiosity of a child, Paul started to grow guppies and algae in his newly acquired aquarium. A few years later, his father bought him a microscope and, for the first time, he was able to explore the invisible world of microorganisms living within his aquarium. He supplemented his observations by reading books that he borrowed from the local public library. In his early teens, Paul discovered and explored a second invisible world—electromagnetic radiation. So began his lifelong quest to understand the “global electronic circuit of life” and the waypoints of Earth's history that led to the establishment of a habitable planet. Life's Engines: How Microbes Made Earth Habitable is a very personal story of Professor Falkowski's own journey through science, interwoven by historical accounts of relevant people and their discoveries in science, humanities, and the arts. The journey includes 11 chapters that step the reader through the origin of our solar system (Chapter 3, The World Before Time), the origin of microbes (Chapter 4, Life's Little Engines), and the eventual emergence of multicellular life forms (Chapter 8, Supersizing in Wonderland). Without a doubt, my personal favorites were Chapter 1 (The Missing Microbes), and Chapter 10 (The Tinkerers). It must have been difficult to cover more than 10 billion years in just 205 pages, but I must admit that Falkowski did a remarkable job highlighting the most significant waypoints in the origin and evolution of planetary metabolism, with appropriate homage to the microbial inhabitants of our planet. Unlike Aquatic Photosynthesis (Falkowski and Raven, second edition, 2013), Life's Engines: How Microbes Made Earth Habitable is not a textbook, an encyclopedic treatise, or a novel, although it has elements of all three. Rather, it is an informative, authoritative, and personal account of “what matters” for planetary sustainability and, therefore, is recommended to all global citizens, taxpayers, and policy makers, regardless of their specific role in society. It is a “must read” for practitioners in the geosciences, especially undergraduate and graduate students with an interest in life on Earth. Finally, I should add that this book is part of Princeton University Press' Science Essential Series that collectively provide a foundation for a better understanding of the scientific and technical advances changing our world. After reading Falkowski's Life Engines: How Microbes Made Earth Habitable, you might wish to check out a few others in the series. I surely will. Reviewed by David M. Karl, Center for Microbial Oceanography: Research and Education (C–MORE), University of Hawaii, C–MORE Hale, 1950 East West Road, Honolulu, HI 96822, USA; dkarl@hawaii.edu