Periods of High Oxygen 15.13 Conclusions Bibliography
19 16 Mass Extinctions 16.1 Extinctions 16.2 What Is Extinction? 16.3 Five Major Mass Extinctions 16.4 Other Extinctions in Earth History 16.5 Causes of Mass Extinction 16.6 The End-Cretaceous Extinction 16.7 The Other Four Big Extinctions of the Phanerozoic 16.8 Do Microorganisms Go Extinct? 16.9 Recovery from Extinction 16.10 Can We Avoid Extinction? 16.11 The Sixth Mass Extinction? 16.12 Conclusions Bibliography
20 17 The Habitability of Planetary Bodies 17.1 What Is “Habitability”? 17.2 The Habitable Zone 17.3 Maintaining Temperature Conditions on a Planet Suitable for Water and Life 17.4 Plate Tectonics and Habitability 17.5 Does the Moon Play a Role in Habitability? 17.6 Other Planetary Factors that Influence Habitability 17.7 Surface Liquid Water, Habitability, and Intelligence 17.8 Habitable Environments Need Not Always Contain Life 17.9 Worlds More Habitable than Earth? 17.10 The Anthropic Principle and Habitability 17.11 The Fate of Earth 17.12 The Galactic Habitable Zone 17.13 The Right Galaxy? 17.14 Conclusions Bibliography
21 18 The Astrobiology of Mars 18.1 Mars and Astrobiology 18.2 Martian Geological History: A Very Brief Summary 18.3 The Environmental Deterioration of Mars 18.4 Missions to Mars 18.5 Mars and Life 18.6 Trajectories of Martian Habitability 18.7 The Viking Program and the Search for Life 18.8 Searching for Life by Investigating Gases 18.9 Martian Meteorites 18.10 Mars Analog Environments 18.11 Panspermia: The Transfer of Life between Planets? 18.12 Conclusions Bibliography
22 19 Ocean Worlds and Icy Moons 19.1 The Astrobiology of Moons 19.2 The Moons of Jupiter: Europa 19.3 The Moons of Jupiter: Ganymede and Callisto 19.4 The Moons of Jupiter: Io 19.5 The Moons of Saturn: Enceladus 19.6 The Moons of Saturn: Titan 19.7 Other Icy Worlds 19.8 Planetary Protection 19.9 Conclusions Bibliography
23 20 Exoplanets and the Search for Life 20.1 Exoplanets and Life 20.2 Detecting Exoplanets 20.3 Exoplanet Properties 20.4 Detecting Life 20.5 Surface Biosignatures 20.6 How Likely Are These Signatures? 20.7 Other Ways to Find Life 20.8 Missions to Detect Biosignatures 20.9 Conclusions Bibliography
24 21 The Search for Extraterrestrial Intelligence 21.1 The Search for Extraterrestrial Intelligence (SETI) 21.2 Methods in the Search for Extraterrestrial Intelligence 21.3 Communication with Extraterrestrial Intelligence (CETI) 21.4