Fortean Times, March 2001

Rare Earth: why complex life is uncommon in the universe
Peter D Ward & Donald Brownlee
New York: Copernicus 2000
hb, $27.50, pp xxviii+333, index, bib, ISBN: 0 387 98701 0

This latest addition to the ever-growing astrobiology shelf takes a different angle to most of the recent glut of volumes on the existence or otherwise of extraterrestrial intelligence. Rather than piling up the evidence for the case that there is some universal life principle that necessarily fills the galaxies with civilisations, Ward and Brownlee argue that while simple microbial life may be common, anything more complex is vanishingly rare.

The almost ubiquitous presence of simple life on Earth, from volcanic deep sea rifts to the undersides of glaciers, suggests that life can exist (and perhaps develop) in the most extreme conditions - conditions which compare to the most inhospitable parts of the Solar system.

But anything more complex than the kind of sludge you find at the back of your fridge appears to be far less likely to develop anywhere. Ward and Brownlee - a geologist and astronomer respectively - spend the bulk of this book detailing the development of the only case of complex life we have to study. Our existence, they argue, is the far-from-inevitable result of a long and complex string of happenstance, from the presence of a Jupiter and large Moon to the timing of ice ages and, perhaps most vitally, the existence of plate tectonics.

Such arguments may be easy to dismiss because, of course, we only have a sample of one to base our theories. But this in itself supports the view that we are, if not alone in the universe, then at least very very lonely.

In the great continuing debate on alien intelligence, Ward and Brownlee clearly and thoroughly present the case against. This is a solid next step for anyone whose appetite was whetted by Peter Brookesmith's "Elephants on Mars" trilogy of articles (FT 134-136).