Rare Earth: Why Complex Life is Uncommon in the Universe
In this exciting new book, distinguished paleontologist Peter D. Ward and noted astronomer Donald Brownlee team up to present a fascinating synthesis of what is now known about the development of life on Earth and how this sheds light on possibilities for organic life forms elsewhere in the Universe. With their broad expertise and wonderful descriptive imagery, the authors provide a compelling argument, a splendid introduction to the emerging field of astrobiology, and a lively discussion of the remarkable findings that are currently being generated.
Offers a fresh and accurate perspective on the most profound question in science – I intelligent life in the Galaxy a dime-a-dozen occurrence or is it a cosmic fluke here on Earth? DLC: Life on other planets.
From the Inside Flap
Maybe we really are alone.
That’s the thought-provoking conclusion of Rare Earth, a book that is certain to have far-reaching impact in the consideration of our place in the cosmos.
While it is widely believed that complex life is common, even widespread, throughout the billions of stars and galaxies of our Universe, astrobiologists Peter Ward and Donald Brownlee argue that advanced life may, in fact, be very rare, perhaps even unique.
Ever since Carl Sagan and Frank Drake announced that extraterrestrial civilizations must number in the millions, the search for life in our galaxy has accelerated. But in this brilliant and carefully argued book, Ward and Brownlee question underlying assumptions of Sagan and Drake’s model, and take us on a search for life that reaches from volcanic hot springs on our ocean floors to the frosty face of Europa, Jupiter’s icy moon. In the process, we learn that while microbial life may well be more prevalent throughout the Universe than previously believed, the conditions necessary for the evolution and survival of higher life—and here the authors consider everything from DNA to plate tectonics to the role of our Moon—are so complex and precarious that they are unlikely to arise in many other places, if at all.
Insightful, well-written, and at the cutting edge of modern scientific investigation, Rare Earth will fascinate anyone interested in the possibility of life elsewhere in the Universe, and offers a fresh perspective on life at home which, if the authors are right, is even more precious than we may ever have imagined.
About the Author(s)
Peter D. Ward is Professor of Geological Sciences and Curator of Paleontology at the University of Washington in Seattle. His previous books include Time Machines and The Call of Distant Mammoths, The End of Evolution and On Methuselah’s Trail, and, with Donald Brownlee, The Life and Death of Planet Earth. A member of the National Academy of Sciences, Donald Brownlee is Professor of Astronomy at the University of Washington in Seattle. He has been a member of numerous important NASA teams, and specializes in the study of the Solar System’s origin, comets and meteorites, and the underlying subject of this book, astrobiology.
Still to early for final conclusions, April 5, 2000
There is a long tradition among humans that we are not aloneinthe universe – that there are other worlds with other intelligentbeings such as ourselves. This tradition is found in many religions and embodied in some scientific thought. The late Carl Sagan, for example, surmised the existence of one million civilizations capable of interstellar communications in the Milky Way galaxy. Ward and Brownlee take exception to these estimates. According to the authors, microbial life is common in the universe "but even the simplest animal life is exceedingly rare." Instead of millions of such civilizations in the Milky Way galaxy there might be just a few. There might be just one.
One of the things I liked most about this book its very nice summary of the history of earth. Chapter 1 has some interesting information about recent discoveries regarding the environments in which extremophiles live. It might seem incredible to us, but extremophiles actually thrive in very high temperatures, pressures, and pH levels that we would find terribly fatal. The wide range of environments in which the simplest life forms can live gives rise to the greater probability of finding them throughout the universe. Extremophiles not only thrive in such environments, they can also tolerate brief forays into space aboard debris ejected from meteor impacts, and they can escape harsh surface conditions by living deep under ground.
The second chapter introduces us to the concept of habitable zones. For extremophiles the habitable zones are quite large, so planets harboring such life can be found in a wider range of orbits around a wider range of stars. More complex life, however, requires far smaller ranges in environmental conditions, leading to a much-reduced habitable zone. Habitable zones must also exist over sufficiently long periods of time for life to evolve. In other words, the habitable zone has both spatial and a temporal components. The upshot is that habitable zones for complex life are pretty small, and may not exist at all unless the star is quite similar to ours.
Chapter three describes some of the critical components for a habitable earth, including the creation of hydrogen and helium (and a bit of lithium) in the Big Bang, and the creation of heavier elements in stars. The earth needed to form from an inter-stellar accumulation rich in metals with the right amount of water. The authors argue that such conditions are rare in the universe, and that planets such as ours are rare as well.
Chapter four discusses the conditions on earth after the initial bombardment stopped, during the earth’s early formation. This chapter has some very interesting material suggesting how bacteria, archaea, and eucarya form the earliest tree of life. Chapter 5 continues by describing how Eucarya are differentiated from the archaeans and the bacteria. Eucarya include the animals, ciliates, fungi, plants, flagellates, and microspordia that constitute the complex life that the authors claim is so rare in the universe. The key piece of evidence regarding eucarya is that they took a long time to evolve in earth’s history. The message in this fact, according to the authors, is that eucarya require a more specialized environment in which to evolve – a narrower habitable zone – and that this environment must persist for long periods of time. All of which argues against this type of life being common in the universe.
Chapter 6 is called "Snowball Earth," and describes the earliest known ice ages on earth, which date to 2.4 billion and 800 to 650 million years BP. These ice ages, in contrast to the one a few tens of thousands of years ago, literally covered the entire earth and froze the oceans over. These ice ages could have helped to stimulate the evolution of animals, and (just as importantly) they also show that major environmental changes – changes that can cause mass extinction – have and can occur on earth. Timing and the extreme nature of the events are critical to the evolution of life.
The real centerpiece of this book is chapter 7, which discusses the enigma of the Cambrian explosion. Perhaps no other event in earth’s history has generated as much debate and speculation as the comparatively sudden rise in complexity of animal species that accompanied the Cambrian explosion. The authors argue that the triggers for this explosion (and they offer several possible candidates) are necessary for the evolution of complex life, but they are also rare – adding further emphasis to their hypothesis that complex life in the universe is rare.
Chapter 8 describes mass extinctions and threats to animal life. Chapter 9 raises some interesting issues about the importance of plate tectonics and argues that the evolution of animal life requires plate tectonics to maintain biodiversity and to stabilize global climate. Chapter 10 discusses the importance of the moon in creating tides, contributing to orbital stability (and possibly contributing to plate tectonics) and Jupiter, which cleans the solar system of planet-crossing projectiles that could sterilize earth. Again, the point is that these conditions are rare, and so planets with complex life are also rare.
Chapter 11 describes ways in which the rare-earth hypothesis might be tested, and chapter 12 reassesses the odds of complex life in the universe via a modified form of the Drake equation. I found chapter 12 a bit of a disappointment, though, since the authors never really stick there necks out and make a claim for how many planets with complex life might exist in the galaxy. The final chapter discusses the philosophical and ethical implications of the rare-earth hypothesis, including the role people play in the current extinction crisis.
This is a first-rate book. The notes are detailed, the index complete, the text clear and understandable. The argument is lucid and in many (though not all) ways compelling. And, of course, it’s hard to think of subject matter more relevant.