Rare Earth

This book argues that the universe is fundamentally hostile to complex life and that while microbial life may be common across the galaxies, complex intelligent life requires an exceptionally unlikely set of circumstances, and must 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.


Peter D. Ward (https://en.wikipedia.org/wiki/Peter_Ward_(paleontologist)) and Donald E. Brownlee (https://en.wikipedia.org/wiki/Donald_E._Brownlee) set out the case that there’s a huge difference between simple and complex life. There is a vast gulf between the simplest self-replicating organic molecules and the immense complexity of metazoans (i.e. multicellular animals). It’s their contention that the path from simplicity to complexity is not a straight line, not an inevitable journey, and fraught with so many dangers and dead ends that it’s a marvel that human beings exist to wonder at the process.


One recently discovered factor is the precise position of Jupiter. The spectacular 1994 impact of Comet Shoemaker-Levy-9 with Jupiter showed how that giant planet protects us from cosmic catastrophe. It acts as an gravitational vacuum cleaner, sucking up incoming debris and preventing it from reaching the inner Solar System. Without Jupiter, life on Earth might have been obliterated long before ever gaining a secure foothold.


Other factors are more local. The presence of a large moon helps to stabilize the Earth’s axial tilt and slow its rotation, keeping climatic variations in check. Geology is also a crucial consideration. By creating mountains, deserts, lakes, and all the other myriad varieties of micro-environment on Earth, plate tectonics allowed the process of speciation – the development of different types of organisms capable of surviving in a greater range of conditions. There was therefore more chance of at least some form of complex life surviving later planetary catastrophes. Further, the heat and movement of the planetary core that drive plate tectonics also create Earth’s magnetic field, shielding its surface from lethal radiation.


All this suggests what a slender foothold complex life really has. The authors describe ten separate mass extinctions on Earth, and many more may have occurred. Each time, some remnant of life has been able to hang on and keep the story going, but there are no guarantees. The continued existence and evolution of complex life is a fine and delicate daisy chain, capable of being broken at any point, and the longer it goes on, the greater the odds against it become. It looks like E.T. may be confined to the celluloid imagination of Steven Spielberg.


Check if this thought-provoking book on astrobiology is in stock at your local library by consulting the online catalogue at https://www.sllclibrary.co.uk/cgi-bin/spydus.exe/MSGTRN/OPAC/BSEARCH



338 pages in Copernicus Press

First published 2000

ISBN 978-0387987019


Professor Peter D. Ward

Scroll to Top