ASTROBIOLOGY Volume 16, Number 8, 2016 Education Article Mary Ann Liebert, Inc. DOI: 10.1089/ast.2015.1460 The Astrobiology Primer v2.0 Co-Lead Editors Shawn D. Domagal-Goldman and Katherine E. Wright Chapter Editors Shawn D. Domagal-Goldman (Co-Lead Editor, Co-Editor Chapter 1, and Author)1,2,* Katherine E. Wright (Co-Lead Editor, Co-Editor Chapter 1, and Author)3,4,* Katarzyna Adamala (Co-Editor Chapter 3 and Author)5 Leigh Arina de la Rubia (Editor Chapter 9 and Author)6 Jade Bond (Co-Editor Chapter 3 and Author)7 Lewis R. Dartnell (Co-Editor Chapter 7 and Author)8 Aaron D. Goldman (Editor Chapter 2 and Author)9 Kennda Lynch (Co-Editor Chapter 5 and Author)10 Marie-Eve Naud (Co-Editor Chapter 7 and Author)11 Ivan G. Paulino-Lima (Editor Chapter 8 and Author)12,13 Kelsi Singer (Co-Editor Chapter 5, Editor Chapter 6, and Author)14 Marina Walter-Antonio (Editor Chapter 4 and Author)15 Authors Ximena C. Abrevaya,16 Rika Anderson,17 Giada Arney,18 Dimitra Atri,13 Armando Azu´a-Bustos,13 Jeff S. Bowman,19 William J. Brazelton,20 Gregory A. Brennecka,21 Regina Carns,22 Aditya Chopra,23 Jesse Colangelo-Lillis,24 Christopher J. Crockett,25 Julia DeMarines,13 Elizabeth A. Frank,26 Carie Frantz,27 Eduardo de la Fuente,28 Douglas Galante,29 Jennifer Glass,30 Damhnait Gleeson,31 Christopher R. Glein,32 Colin Goldblatt,33 Rachel Horak,34 Lev Horodyskyj,35 Betu¨l Kac¸ar,36 Akos Kereszturi,37 Emily Knowles,38 Paul Mayeur,39 Shawn McGlynn,40 Yamila Miguel,41 Michelle Montgomery,42 Catherine Neish,43 Lena Noack,44 Sarah Rugheimer,45,46 Eva E. Stu¨eken,47,48 Paulina Tamez-Hidalgo,49 Sara Imari Walker,13,50 and Teresa Wong51 *These two authors contributed equally to the work. 1NASA Goddard Space Flight Center, Greenbelt, Maryland, USA. 2Virtual Planetary Laboratory, Seattle, Washington, USA. 3University of Colorado at Boulder, Colorado, USA. 4Present address: UK Space Agency, UK. 5Department of Genetics, Cell Biology and Development, University of Minnesota, Minneapolis, Minnesota, USA. 6Tennessee State University, Nashville, Tennessee, USA. 7Department of Physics, University of New South Wales, Sydney, Australia. 8University of Westminster, London, UK. 9Oberlin College, Oberlin, Ohio, USA. 10Division of Biological Sciences, University of Montana, Missoula, Montana, USA. 11Institute for research on exoplanets (iREx), Universite´ de Montre´al, Montre´al, Canada. 12Universities Space Research Association, Mountain View, California, USA. 13Blue Marble Space Institute of Science, Seattle, Washington, USA. 14Southwest Research Institute, Boulder, Colorado, USA. 15Mayo Clinic, Rochester, Minnesota, USA. 16Instituto de Astronomı´ayFı´sica del Espacio (IAFE), UBA—CONICET, Ciudad Auto´noma de Buenos Aires, Argentina. 17Department of Biology, Carleton College, Northfield, Minnesota, USA. 18University of Washington Astronomy Department and Astrobiology Program, Seattle, Washington, USA. 19Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York, USA. 20Department of Biology, University of Utah, Salt Lake City, Utah, USA. 21Institut fu¨r Planetologie, University of Mu¨nster, Mu¨nster, Germany. 22Polar Science Center, Applied Physics Laboratory, University of Washington, Seattle, Washington, USA. 23Planetary Science Institute, Research School of Earth Sciences, Research School of Astronomy and Astrophysics, The Australian National University, Canberra, Australia. 561 562 DOMAGAL-GOLDMAN AND WRIGHT ET AL. Table of Contents Chapter 1. Introduction—What Is Astrobiology? 562 Chapter 2. What Is Life? 563 Chapter 3. How Did Earth and Its Biosphere Originate? 565 Chapter 4. How Have Earth and Its Biosphere Evolved? 582 Chapter 5. What Does Life on Earth Tell Us about Habitability? 589 Chapter 6. What Is Known about Potentially Habitable Worlds beyond Earth? 597 Chapter 7. What Are the Signs of Life (Biosignatures) That We Could Use to Look for Life beyond Earth? 613 Chapter 8. What Relevance Does Astrobiology Have to the Future of Life on This Planet? 623 Chapter 9. Resources 626 Acknowledgments 627 References 627 Abbreviations List 653 Chapter 1. Introduction—What Is Astrobiology? life in the Universe in a holistic way, astrobiology asks ques- tions that transcend all these individual scientific subjects. 1.1. What is astrobiology? Astrobiological research potentially has much broader strobiology is the science that seeks to understand the consequences than simply scientific discovery, as it includes Astory of life in our universe. Astrobiology includes inves- questions that have been of great interest to human beings tigation of the conditions that are necessary for life to emerge for millennia (e.g., are we alone?) and raises issues that and flourish, the origin of life, the ways that life has evolved and could affect the way the human race views and conducts adapted to the wide range of environmental conditions here on itself as a species (e.g., what are our ethical responsibilities Earth, the search for life beyond Earth, the habitability of ex- to any life discovered beyond Earth?). traterrestrial environments, and consideration of the future of life here on Earth and elsewhere. It therefore requires knowl- 1.2. Have we already found life beyond Earth? edge of physics, chemistry, biology, and many more specialized scientific areas including astronomy, geology, planetary sci- No. There have been many exciting discoveries that ence, microbiology, atmospheric science, and oceanography. suggest life is possible on other planets and moons, but we However, astrobiology is more than just a collection of have not yet detected any definite signs of life beyond Earth. different disciplines. In seeking to understand the full story of That does not necessarily mean life exists only on Earth, but 24Earth and Planetary Science, McGill University, and the McGill Space Institute, Montre´al, Canada. 25Society for Science & the Public, Washington, DC, USA. 26Carnegie Institute for Science, Washington, DC, USA. 27Department of Geosciences, Weber State University, Ogden, Utah, USA. 28IAM-Departamento de Fisica, CUCEI, Universidad de Guadalajara, Guadalajara, Me´xico. 29Brazilian Synchrotron Light Laboratory, Campinas, Brazil. 30School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georgia, USA. 31Science Foundation Ireland, Dublin, Ireland. 32Southwest Research Institute, San Antonio, Texas, USA. 33School of Earth and Ocean Sciences, University of Victoria, Victoria, Canada. 34American Society for Microbiology, Washington, DC, USA. 35Arizona State University, Tempe, Arizona, USA. 36Harvard University, Organismic and Evolutionary Biology, Cambridge, Massachusetts, USA. 37Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences, Budapest, Hungary. 38Johnson & Wales University, Denver, Colorado, USA. 39Rensselaer Polytechnic Institute, Troy, New York, USA. 40Earth Life Science Institute, Tokyo Institute of Technology, Tokyo, Japan. 41Laboratoire Lagrange, UMR 7293, Universite´ Nice Sophia Antipolis, CNRS, Observatoire de la Coˆte d’Azur, Nice, France. 42University of Central Florida, Orlando, Florida, USA. 43Department of Earth Sciences, The University of Western Ontario, London, Canada. 44Royal Observatory of Belgium, Brussels, Belgium. 45Department of Astronomy, Harvard University, Cambridge, Massachusetts, USA. 46University of St. Andrews, St. Andrews, UK. 47University of Washington, Seattle, Washington, USA. 48University of California, Riverside, California, USA. 49Novozymes A/S, Bagsvaerd, Denmark. 50School of Earth and Space Exploration and Beyond Center for Fundamental Concepts in Science, Arizona State University, Tempe, Arizona, USA. 51Department of Earth and Planetary Sciences, Washington University in St. Louis, St. Louis, Missouri, USA. ª Shawn D. Domagal-Goldman and Katherine E. Wright, et al., 2016; Published by Mary Ann Liebert, Inc. This Open Access article is distributed under the terms of the Creative Commons Attribution Noncommercial License (http://creativecommons.org/licenses/by-nc/4.0/) which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and the source are credited. THE ASTROBIOLOGY PRIMER 563 only that there is not yet compelling evidence for its exis- It is longer than a typical review paper but much shorter in tence elsewhere. Space missions have explored only a tiny length than a textbook, with the goal of being detailed en- portion of our solar system, and in the few years since we ough to provide a brief overview of the variety of questions first discovered planets around other stars, the number of investigated by astrobiologists. such exoplanets known has increased into the hundreds. The The Astrobiology Primer is the product of a strong, vi- search for life beyond Earth has therefore only just begun. brant, early-career astrobiology community. This is the Astrobiology is an exciting subject with new ideas that second version of the Primer, and like the first (Mix et al., can easily capture the imaginations of both scientists and 2006), it is a grassroots effort, written by graduate students nonscientists. But like all areas of science, new ideas are and postdoctoral researchers. In total, we are a group of 49 subject to detailed scrutiny by the scientific community as authors and editors from 14 different countries. This second part of the quality control process. Only ideas that are edition has been rewritten from scratch. It updates content considered to be well-supported by evidence are accepted by and is organized