Rare Earth (book)

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Rare Earth: Why Complex Life Is Uncommon in the Universe
Rare Earth -- Why Complex Life Is Uncommon in the Universe.jpg
AuthorsPeter D. Ward
Donald E. Brownlee
CountryUnited States
Publication date
Media typePrint
Pages338 pp.

Rare Earth: Why Complex Life Is Uncommon in the Universe is a 2000 popular science book about xenobiology by Peter Ward, a geologist and evolutionary biologist, and Donald E. Brownlee, a cosmologist and astrobiologist, both faculty members at the University of Washington. The book is the origin of the term 'Rare Earth Hypothesis' which, like the book, asserts the concept that complex life is rare in the universe. The book was eventually succeeded by a follow-up book called The Life and Death of Planet Earth: How the New Science of Astrobiology Charts the Ultimate Fate of our World, also by Ward and Brownlee, which talks about the Earth's long term future and eventual demise under a warming and expanding Sun, showing readers the concept that planets like Earth have finite lifespans, and complex life is not just rare in space, but also rare in time, and is more likely to die out within a short time on geological timescales, while microbes dominate most of the planet's history.


The book argues that the universe is fundamentally hostile to complex life and that while microbial life may be common in the universe, complex intelligent life (like the evolution of biological complexity from simple life on Earth) required an exceptionally unlikely set of circumstances, and therefore complex life is likely to be extremely rare. The book argues that among the essential criteria for life are a terrestrial planet with plate tectonics and oxygen, a large moon, magnetic field, a gas giant like Jupiter for protection and an orbit in the habitable zone of the right kind of star.


Rare Earth attracted substantial attention, both in the media and academically. It has been cited by many subsequent articles in the field of geology and astrobiology. Christopher McKay wrote a positive review titled 'All Alone After All?', in the journal Science.[1] The Times proclaimed it as an answer to the Copernican Principle.[2] Discover described it as a "a wet blanket for E.T. enthusiasts".[2] The book's rationale was also praised by media outlets including Newsday and The Economist. CNN described it as an answer to the Fermi paradox.[2] Several astronomy sources also praised the book including Sky & Telescope and Astronomy magazine. Other science media also praised the book including American Scientist, Popular Mechanics, and Physics Today.[2] Ward & Brownlee's Rare Earth Hypothesis has been further popularised in books along the same theme.

It was not without its critics, however. While initially declaring it a "must read",[2] James Kasting wrote a highly critical reply in the journal Perspectives in Biology and Medicine, challenging its restrictive criteria.[3] Several books were written in reply including Evolving the Alien by Jack Cohen, who described Ward & Brownlee's assumption as restrictive and unimaginative; and a form of circular reasoning.[4] The book Life Everywhere by David Darling was also written largely in reply to Rare Earth and Darling describes it as neither a hypothesis nor prediction, but merely "a description of how life arose on Earth" having selected the factors that best suit the case.[5]

What matters is not whether there's anything unusual about the Earth; there's going to be something idiosyncratic about every planet in space. What matters is whether any of Earth's circumstances are not only unusual but also essential for complex life. So far we've seen nothing to suggest there is.[6]

According to Robert K. Logan there is very little surprise as to why the book received significant interest from the neo-creationism movement. While Ward & Brownlee attribute this exceptional unlikeliness to chance, many within the movement regard this as evidence of an intelligent designer.[7] Many subsequent intelligent design advocates have been inspired by Rare Earth including Guillermo Gonzalez who wrote and the book The Privileged Planet promoting the concept of intelligent design. Gonzalez coined the term Galactic Habitable Zone based on the work 'The Galactic Habitable Zone: Galactic Chemical Evolution', a collaboration with Ward & Brownlee.[8]

See also[edit]


  1. ^ Science Magazine. Volume 288, Number 5466, Issue of 28 Apr 2000, p. 625.
  2. ^ a b c d e Ward & Brownlee 2000
  3. ^ Kasting 2001
  4. ^ Krauss, Lawrence M. (January 9, 2003). "Aliens Unlimited". Nature. 421: 114–115. Bibcode:2003Natur.421..114K. doi:10.1038/421114a.
  5. ^ Darling, David (2001). Life Everywhere: The Maverick Science of Astrobiology. Basic Books/Perseus. ISBN 0-585-41822-5.
  6. ^ Darling 2001, p. 103
  7. ^ Robert K. Logan (2010). The Poetry of Physics and the Physics of Poetry. World Scientific. pp. 279–. ISBN 978-981-4295-94-9.
  8. ^ Gonzalez, Brownlee & Ward 2001