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  Astrobiology: A Very Short Introduction

  ASTROBIOLOGY

  A Very Short Introduction

  David C. Catling

  Contents

  Acknowledgements

  List of illustrations

  1 What is astrobiology?

  2 From stardust to planets, the abodes for life

  3 Origins of life and environment

  4 From slime to the sublime

  5 Life: a genome’s way of making more and fitter genomes

  6 Life in the Solar System

  7 Far-off worlds, distant suns

  8 Controversies and prospects

  Further reading

  Index

  Acknowledgements

  I thank Professor John Armstrong, Dr Rory Barnes, Professor John Baross, Dr Billy Brazelton, Professor Roger Buick, Dr Rachel Horak, Imelda Kirby, and Professor Woody Sullivan for reading parts of the manuscript and offering various corrections and suggestions. Thanks also to Latha Menon and Mimi Southwood, who read the entire manuscript, the latter offering the perspective of a non-scientist. Numerous students who attended my astrobiology classes at the University of Washington over the years also helped me mentally prepare for writing this book. At Oxford University Press, I thank Emma Ma and Latha Menon for their encouragement and assistance.

  List of illustrations

  1 The Hertzsprung–Russell diagramr />
  Adapted from ‘Stellar Evolution and Social Evolution: A Study in Parallel Processes’ (2005), Social Evolution & History. 4: 1, 136–59), reproduced with permission of Professor Robert Carneiro

  2 Left: Cross-section of the world’s oldest fossil stromatolites Right: A plan view of the bedding plane of the stromatolites

  Photographs by David C. Catling

  3 The approximate history of atmospheric oxygen

  Author’s own diagram

  4 a) Schematic of prokaryote (archaea and bacteria) versus eukaryote structure; b) Two bacteria caught in the act of conjugation

  b) Credit: Charles C. Brinton Jr. and Judith Carnahan

  5 Left: DNA consists of two strands connected together. Right: In three dimensions, each strand is a helix, so that overall we have a ‘double helix’

  6 The classification scheme for metabolisms in terrestrial life

  7 The ‘tree of life’ constructed from ribosomal RNA

  8 a) Valley networks on Mars; b) Outflow channel Ravi Vallis

  a) ESA/DLR/FU Berlin

  (G. Neukum); b) NASA/JPL/Caltech/Arizona State University

  9 The Galilean moons of Jupiter: Io, Europa, Ganymede, and Callisto

  NASA/JPL/DLR

  10 a) A network of channels that appear to flow into a plain near the Huygens landing site; b) Image of the surface at the Huygens landing site.

  Courtesy of ESA/NASA/University of Arizona

  11 Brain and body mass for some different mammals.

  Adapted from Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology, Vol. 136: 4, Hassiotis, M., Paxinos, G., and Ashwell, K. W. S., ‘The anatomy of the cerebral cortex of the echidna (Tachyglossus aculeatus)’, 827–50. Copyright (2003), with permission from Elsevier

  Chapter 1

  What is astrobiology?

  Behind the name

  ‘What the hell is astrobiology?’ an American Secret Service agent cried into his walkie-talkie. He had just been checking the identity of an academic visitor to NASA’s Ames Research Center, near San Francisco. The visitor had said that he was attending NASA’s first astrobiology science conference. Ames has an airstrip that provides a secure landing site for Air Force One, and, in April 2000, President Bill Clinton had just flown in to visit the San Francisco Bay area, bringing along his Secret Service entourage.

  The agent’s question was a fair one. It was only in the late 1990s that a scientific consensus emerged about the meaning of astrobiology. Few laymen or Secret Service agents would have heard of the term. Back then, NASA began to promote a research programme in astrobiology led by Ames, where I was working as a space scientist. At first, some of my colleagues disliked the literal Greek meaning of the ‘biology of stars’. One noted with a scoff how life couldn’t exist inside the infernos of stars. A less curmudgeonly interpretation is that the ‘astro’ in astrobiology concerns life around stars, including the Sun, or simply life in space. In fact, many astrobiologists are as much concerned with the history of life on Earth as with life elsewhere. Astrobiologists agree that we should have a firm understanding of how life evolved on Earth in order to ponder the existence of life in outer space. Yet one of the astonishing aspects of modern science is that it has so far failed to answer questions about biology that even a child might ask. How did life on Earth get started? We have some ideas but the details are unknown. Which special properties of the Earth and the Solar System make our planet habitable? Again, some thoughts but there is still much to learn. And what caused life to evolve into complex organisms instead of remaining simple? Again, we’re uncertain.