Davies - The origin of life

PENGUIN BOOKS

THE ORIGIN OF LIFE

Paul Davies is an internationally acclaimed physicist, writer and broadcaster, who holds the position of Professor of Natural Philosophy in the Australian Centre for Astrobiology at Macquarie University, Sydney. He has held previous academic appointments at the Universities of Cambridge, London, Newcastle upon Tyne and Adelaide. His research interests are in the fields of cosmology, quantum field theory and astrobiology. He is the author of over twenty books, including The Mind of God, About Time and How to Build a Time Machine.

Davies's talent as a communicator of science has been recognized in Australia by an Advance Australia Award and two Eureka Prizes, and in the UK by the 2001 Kelvin Medal and Prize by the Institute of Physics, and the 2002 Faraday Prize by the Royal Society. For his contributions to the deeper implications of science, Davies received the Templeton Prize in 1995.

Paul Davies

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PENGUIN BOOKS

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First published as The Fifth Miracle by Allen Lane The Penguin Press 1998

Published in Penguin Books 1999

Reissued 2000

Reprinted, with updates, under the present title 2003

Copyright Orion Productions,1998, 2003

copyright Karl Stetter, 1998

copyright Novartis Foundations, 1998

All rights reserved

The moral right of the author has been asserted

978-0-14-194183-7

In memory of Keith Runcorn

A pivotal event in the history of science came in 1859 with the publication by Charles Darwin of his opus On the Origin of Species. that it seems almost a miracle, so many are the conditions which would have to be satisfied to get it going.

In a nutshell, the problem is this. How did a mixture of lifeless atoms subject to blind and purposeless forces assemble themselves into something as awesomely complex as even the simplest microbe? Where and when did this momentous event take place? Did it happen only once in the universe, the result of a bizarre chemical fluke, or are the laws of nature inherently bio-friendly, implying that life will emerge wherever in the universe there are earthlike planets?

Belief that life is deeply etched into the laws of nature carries a faint echo of a bygone religious age, of a universe designed for habitation by living creatures. Many scientists are scornful of such notions, insisting that life's beginning was a freak accident of chemistry, unique to Earth, and that the subsequent emergence of complex organisms, including conscious beings, is likewise purely the chance outcome of a gigantic molecular If de Duve is right, the universe will be teeming with life.

There is a lot at stake in this debate, for it concerns the very place of mankind in the cosmos whether or not we are alone and where we fit into the grand scheme of things. It also has implications for technology. If life emerges readily, there is a good chance we shall be able to make it from scratch in the laboratory; many biochemists are currently busy trying to do just that. Novel life forms might revolutionize biotechnology and molecular biology. They could also pave the way to terra-forming other planets making them more like Earth perhaps eventually making them suitable for human habitation. Creating life in a test tube would also go a long way to removing the shroud of mystery over how it began naturally.

The study of life's origin and distribution in the universe forms part of the subject known as astrobiology. Scientists increasingly recognize that the story of life is not confined to our planet, but extends into interplanetary and even interstellar space. The holy grail of astrobiology is to identify a second genesis another planet where life has arisen independently. By common consent Mars offers the best hope for finding life beyond Earth, though within our solar system Europa, a moon of Jupiter, is increasingly seen as a promising candidate too. Mars is currently the subject of intense astrobiological research, and the destination of many current and planned space missions. Although it is a freeze-dried desert today, in the past it was warm and wet, and not dissimilar to Earth. Four billion years ago, Mars may even have offered a more favourable habitat for life than our own planet.

Indeed, it is not clear that terrestrial life actually started here on Earth. In the early 1990s Jay Melosh, of the University of Arizona, and I independently suggested that live microbes might be conveyed inside rocks blasted off planets by asteroid and comet impacts. Some of these rocks could find their way to neighbouring planets and implant life there. In particular, rocks ejected from Mars might bring Martian microbes to Earth, perhaps seeding our planet with its first life forms. If so, we could all be descended from Martians! Conversely, terrestrial rocks will have made their way to Mars, possibly colonizing it with earthly bacteria. Either way, it seems that Earth and Mars are not biologically isolated. Fascinating though this may be, it complicates attempts to establish any independent second genesis on Mars, as the two planets have most likely contaminated each other.

Since Melosh and I first presented these ideas, they have become widely accepted. The basic scenario was strongly supported in a comprehensive study carried out by Curt Mileikowsky and his colleagues, published in the journal Icarus. The investigators considered all the hazards faced by a microbe propelled from Mars to Earth or vice versa, with special attention being given to radiation damage. The authors concluded that if microbes existed or exist on Mars, viable transfer to Earth is not only possible but also highly probable Earth-to-Mars transfer is also possible but at a much lower frequency.

One event that brought the idea of microbes travelling between planets to prominence was the extraordinary announcement in August 1996 by President Bill Clinton that NASA had discovered evidence for life on Mars. The discovery concerned a meterorite found in Antarctica in 1984, later identified to have come from Mars. To date, over twenty Mars meteorites have been found, each of them ejected by cosmic impacts on the Red Planet. The rock of interest, about the size of a large potato, contains tiny features reminiscent of fossilized bacteria. Could these be remnants of Martian microbes?

The debate has raged for several years, without clear conclusion. Detractors say the little blobs in the rock are just

Though Darwin refused to be drawn about the mechanism of life's origin, he did speculate in a letter to a friend that a warm little pond somewhere on Earths ancient surface might have slowly accumulated a rich mix of chemicals. Then, driven by the energy of sunlight, molecules of ever-greater complexity might have formed until the brew somehow incubated life. Darwin's idea eventually metamorphosed into the well-known primordial soup theory.