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E-grāmata: Astrobiology: An Introduction

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(Associate Lecturer in Astronomy and Earth Sciences, Open University, UK)
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Astrobiology: An IntroductionPalielināt
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Longstaff presents a textbook introducing astrobiology to students in any of the scientific disciplines that it draws on, particularly astronomy, physical sciences, Earth sciences, and biology. He uses no calculus or curly-arrow chemistry, nor details of modeling; he does include reminders of fundamental matters of physics and chemistry at strategic spots to keep keep students from getting derailed. His topics include origins of the elements, properties of life, terrestrial biochemistry, Mars, and exoplanetary systems. Annotation ©2015 Ringgold, Inc., Portland, OR (protoview.com)

Astrobiology is a multidisciplinary pursuit that in various guises encompasses astronomy, chemistry, planetary and Earth sciences, and biology. It relies on mathematical, statistical, and computer modeling for theory, and space science, engineering, and computing to implement observational and experimental work. Consequently, when studying astrobiology, a broad scientific canvas is needed. For example, it is now clear that the Earth operates as a system; it is no longer appropriate to think in terms of geology, oceans, atmosphere, and life as being separate.

Reflecting this multiscience approach, Astrobiology: An Introduction:

  • Covers topics such as stellar evolution, cosmic chemistry, planet formation, habitable zones, terrestrial biochemistry, and exoplanetary systems
  • Discusses the origin, evolution, distribution, and future of life in the universe in an accessible manner, sparing calculus, curly arrow chemistry, and modeling details
  • Contains problems and worked examples, and includes a solutions manual with qualifying course adoption

Astrobiology: An Introduction provides a full introduction to astrobiology suitable for university students at all levels.

Constants xxv
Acknowledgments xxvii
Author xxix
Introduction xxxi
1 Origin of the Elements 1(32)
1.1 Elements for Life
1(1)
1.2 The Universe Started from a Hot and Dense State
1(3)
1.2.1 Abundances of Primordial Elements Are Predicted by the Big Bang Hypothesis
1(3)
1.2.1.1 The Early Universe Was Dominated by Radiation
1(1)
1.2.1.2 Primordial Hydrogen and Helium Were Synthesized in the First 20 min
2(2)
1.2.1.3 Lithium Abundance Is Problematic
4(1)
1.3 The Message of Light
4(12)
1.3.1 Atoms and Molecules Process Electromagnetic Radiation
4(2)
1.3.2 Electronic Transitions Are Quantized
6(2)
1.3.3 Energy Levels Govern Electronic Transitions in the Hydrogen Atom
8(3)
1.3.4 Spectrographs Are Used to Capture Spectra
11(1)
1.3.5 Stellar Spectra Encode Temperature and Elemental Abundances
11(5)
1.3.5.1 Harvard Spectral Classification Is Based on the Strength of Absorption Lines
12(2)
1.3.5.2 Luminosity Classes Are Based on the Sizes of Stars
14(1)
1.3.5.3 A Plot of Luminosity against Temperature Is a Hertzsprung—Russell Diagram
15(1)
1.4 Stellar Evolution
16(17)
1.4.1 The Properties of Main Sequence Stars Are Determined by Their Masses
17(2)
1.4.1.1 Brown Dwarfs Are Not Massive Enough to Become Stars
18(1)
1.4.1.2 The Boundary between Brown Dwarf and Planet Is Hard to Define
18(1)
1.4.1.3 The Upper Limit for Stellar Masses Is Not Well Defined
19(1)
1.4.2 Stars Form by the Collapse of Giant Molecular Clouds
19(3)
1.4.2.1 Cloud Collapse Can Be Modeled by Simple Physics
20(1)
1.4.2.2 Any Plausible Model of Star Formation Must Be Able to Explain Several Key Facts
21(1)
1.4.2.3 Fragmentation and Accretion Are Key Processes in Star Formation
21(1)
1.4.3 Protostars Contract Down Onto the Main Sequence
22(1)
1.4.3.1 Initial Protostar Contraction Is Isothermal
22(1)
1.4.3.2 Contraction onto the Main Sequence
22(1)
1.4.4 Main Sequence Stars Fuse Hydrogen to Helium
22(2)
1.4.4.1 Proton—Proton (PP) Chains Are the Main Energy Yielding Fusion Reactions in Main Sequence Stars
23(1)
1.4.4.2 Stars Process γ Radiation to Lower Energy Radiation
24(1)
1.4.5 Many Low Mass Stars Become Red Giants
24(4)
1.4.5.1 Hydrogen Fusion Moves from Core to Shell
24(1)
1.4.5.2 Core Fusion Reactions Generate Carbon and Oxygen in Red Giant Stars
25(1)
1.4.5.3 Asymptotic Giant Branch (AGB) Stars Build Elements by Slow Neutron Capture
26(1)
1.4.5.4 AGB Stars Distribute Metals into the Interstellar Medium
27(1)
1.4.5.5 Very Low Mass Stars Do Not Alter the Interstellar Medium
27(1)
1.4.6 High Mass Stars Make High Mass Elements
28(5)
1.4.6.1 Red Supergiants Can Forge Elements up to Iron
28(1)
1.4.6.2 Core Collapse Supernovae Forms r-Process Elements
29(2)
1.4.6.3 Supernova Remnants Seed the Interstellar Medium with Elements
31(2)
2 The Chemistry of Space 33(30)
2.1 From Elements to Molecules
33(1)
2.2 Astrochemical Environments
33(11)
2.2.1 Cool Stars Have Molecular Absorption Lines
33(1)
2.2.2 The Interstellar Medium Is Extremely Tenuous
33(4)
2.2.2.1 Warm—Hot ISM Pervades Most of the Space between the Stars
34(1)
2.2.2.2 Atomic and Molecular Hydrogen Dominates Diffuse and Dense Clouds
35(2)
2.2.3 The ISM Contains Dust Grains
37(2)
2.2.4 AGB Stars Have Either Oxygen- or Carbon-Rich Atmospheres
39(1)
2.2.4.1 Fusion Products Are Convected into the Atmospheres of AGB Stars
39(1)
2.2.4.2 C/O Ratio Is the Key to Stellar Chemistry
39(1)
2.2.5 Doing Chemistry in Space
40(3)
2.2.5.1 Astrochemistry Happens Over a Wide Temperature Range
40(1)
2.2.5.2 Astrochemistry Happens at Extraordinarily Low Densities
41(1)
2.2.5.3 Reaction Rate Constants Describe Reaction Rates
41(2)
2.2.6 Different Chemistry Operates in Dense Clouds and Diffuse Clouds
43(1)
2.2.6.1 Dense Clouds Provide Safe Haven for Molecules
43(1)
2.3 Molecular Spectroscopy
44(7)
2.3.1 Molecules Are Detected Mostly by Vibrational and Rotational Spectra
44(7)
2.3.1.1 Molecular Vibrations Are Quantized
44(1)
2.3.1.2 Molecules Are Similar to Springs
44(2)
2.3.1.3 Not All Vibrations Are Infrared Active
46(1)
2.3.1.4 Molecular Rotations Are Quantized
47(1)
2.3.1.5 Rotational—Vibrational Spectra
48(2)
2.3.1.6 Isotopes Can Be Distinguished by Rotational Spectra
50(1)
2.3.1.7 Temperature Can Be Deduced from Rotational Spectra
50(1)
2.3.1.8 Polyatomic Molecules
50(1)
2.3.1.9 Electronic States of Molecules
50(1)
2.4 Building Molecules
51(3)
2.4.1 Molecules in the ISM
51(1)
2.4.2 Reaction Mechanisms
51(3)
2.4.2.1 Ionization
51(1)
2.4.2.2 Atomic Photoionization
51(1)
2.4.2.3 Molecular Photoionization
52(1)
2.4.2.4 Cosmic Ray Ionization
52(1)
2.4.2.5 Photodissociation
52(1)
2.4.2.6 Dissociative Recombination
53(1)
2.4.2.7 Dissociative Recombination of Molecules Is Fast and Common
53(1)
2.4.2.8 Neutral Chemistry
53(1)
2.4.2.9 Ion—Molecule Reactions
54(1)
2.5 Chemical Networks
54(9)
2.5.1 Dust Grain Surfaces Catalyze Synthesis of Hydrogen Molecules
54(6)
2.5.1.1 Molecular Hydrogen Is Protected by Self-Shielding
55(1)
2.5.1.2 Grain Surfaces Are Important for Oxygen Chemistry
56(1)
2.5.1.3 Methanol Synthesis Involves Grain Surfaces
56(1)
2.5.1.4 Diffuse Clouds Are Photon-Dominated Regions
56(1)
2.5.1.5 X-Ray-Dominated Regions
57(1)
2.5.1.6 H+3 Is the Starting Point for a Great Deal of Chemistry
58(1)
2.5.1.7 Hydrocarbon Synthesis from H+3 Gives Methane
59(1)
2.5.1.8 The C+ Ion Is a Starting Point for PDR Chemistry
59(1)
2.5.1.9 Nitrogen Chemistry Yields Ammonia
60(1)
2.5.2 Chemical Species Can Trace ISM Conditions and Processes
60(3)
2.5.2.1 CN, HCN, and NHC Are Intimately Related
60(1)
2.5.2.2 HCN and Friends Provide Clues to the State of the ISM
61(2)
3 Habitable Earth 63(28)
3.1 Earth in Context
63(5)
3.1.1 There Are Eight Major Planets
63(2)
3.1.1.1 Terrestrial Planets Have Low Masses
63(1)
3.1.1.2 Gas and Ice Giants Have High Masses
63(1)
3.1.1.3 Most Planets Have Moons
64(1)
3.1.1.4 Many Solar System Bodies Are Differentiated
65(1)
3.1.2 The Planets Were Condensed from a Spinning Disc
65(1)
3.1.3 The Solar System Contains Numerous Small Bodies
65(2)
3.1.3.1 The Scattered Kuiper Belt Is the Source of Jupiter Family Short-Period Comets
66(1)
3.1.3.2 The Oort Cloud Is the Source of Halley Family Short-Period and Long-Period Comets
66(1)
3.1.3.3 Asteroids Sample Very Early Solar System Material
67(1)
3.1.4 What Is a Planet?
67(1)
3.1.4.1 A Planet Must Satisfy Three Criteria
67(1)
3.2 Habitability Is an Attribute of the Entire Earth System
68(2)
3.2.1 The Structure and Composition of the Solid Earth
68(1)
3.2.2 The Chondritic Earth Model Provides a First Approximation to Its Bulk Composition
68(1)
3.2.3 Seismology Provides a Picture of the Earth's Interior
69(1)
3.3 What Makes Earth Habitable?
70(13)
3.3.1 Temperature at the Earth's Surface Is Largely Determined by the Sun
71(1)
3.3.2 Liquid Water Exists on the Earth's Surface
72(1)
3.3.3 Earth Is in a Stable Orbit in the Habitable Zone
73(3)
3.3.3.1 The Inner Edge of the Habitable Zone Is Defined by the Moist Greenhouse Effect
74(1)
3.3.3.2 The Outer Boundary of the Habitable Zone Is Defined by Maximum CO2 Greenhouse
75(1)
3.3.3.3 The Habitable Zone Changes with Time
75(1)
3.3.3.4 Habitable Zones Are Defined for Exoplanet Systems
75(1)
3.3.4 Earth's Dense Atmosphere Contributes to Habitability
76(4)
3.3.4.1 A Planet's Mass Determines What Gases It Can Retain
76(4)
3.3.5 A Global Magnetic Field May Be Required for Habitability
80(3)
3.3.5.1 Earth's Magnetic Field Helps It Retain Its Atmosphere
80(1)
3.3.5.2 Earth's Atmosphere Has Been Shielded by a Magnetic Field for at Least 3 Gyr
81(1)
3.3.5.3 Mars Lacks a Magnetic Field and Has Lost Much of Its Atmosphere
81(1)
3.3.5.4 Venus Lacks a Magnetic Field yet Has a Dense Atmosphere
81(1)
3.3.5.5 A Global Magnetic Field Requires a Liquid Core
81(1)
3.3.5.6 The Core Has a Light Element That Is Crucial for the Geodynamo
82(1)
3.3.5.7 Why do Mars and Venus Lack Magnetic Fields?
82(1)
3.4 Earth Seems Unique in Having Plate Tectonics
83(8)
3.4.1 Plate Tectonics Depends on a Weak Mantle Layer
83(1)
3.4.2 New Ocean Crust Is Made at Constructive Plate Boundaries
84(1)
3.4.3 Ocean Crust Is Destroyed at Destructive Plate Boundaries
84(1)
3.4.4 Hot Spot Volcanism: Evidence for Mantle Convection?
85(1)
3.4.5 Plate Tectonics Is Self-Regulating
85(4)
3.4.5.1 The Carbonate—Silicate Cycle Is a Planetary Thermostat
86(1)
3.4.5.2 Silicate Weathering Reduces Atmospheric CO2
87(1)
3.4.5.3 Subduction Volcanism Increases Atmospheric CO2
88(1)
3.4.5.4 The Carbonate—Silicate Cycle Regulates Temperature by Negative Feedback
88(1)
3.4.6 Plate Tectonics May Be Required for Habitability
89(1)
3.4.7 Plate Tectonics Seems Not to Operate on Mars or Venus
89(2)
4 Building the Solar System 91(26)
4.1 Planet Formation Is Contingent
91(1)
4.2 Planets Formed by Accretion from the Solar Nebula
91(11)
4.2.1 The Solar Nebula Was a Dynamic Environment
91(1)
4.2.2 The Solar Nebula Formed a Spinning Disc
92(1)
4.2.3 Planet and Star Formation Occur Together
92(1)
4.2.4 Condensation of Solids from the Solar Nebula Depended on Temperature
93(2)
4.2.4.1 The First Solids Condensed in the Solar Nebula 4.567 Gyr ago
95(1)
4.2.5 Accretion Involves Several Distinct Mechanisms
95(4)
4.2.5.1 Cohesion Builds Particles a Few Millimeters in Size
95(1)
4.2.5.2 Chondrules Formed in Episodes of Intense Heating
95(3)
4.2.5.3 Assembly of Planetesimals Is Poorly Understood
98(1)
4.2.5.4 Runaway Growth Builds Oligarchs and Planetary Embryos
98(1)
4.2.5.5 Debris Discs Result from End Stages of Planet Building
99(1)
4.2.6 Heat Sources Drive Differentiation
99(1)
4.2.6.1 Vesta Is an Ancient Differentiated World
100(1)
4.2.7 Differentiation Redistributes Elements
100(1)
4.2.7.1 Elements Have Distinct Chemical Affinities
100(1)
4.2.8 Gas Giants Must Have Assembled Within a Few Million Years
101(1)
4.2.9 Accretion of Terrestrial Planets Took Tens of Millions of Years
102(1)
4.3 The Solar System Started with a Bang
102(2)
4.3.1 26Mg Traces the Original 26Al
102(1)
4.3.2 Did the Decay of 26Al Make Life on Earth Possible?
103(1)
4.4 Dating Events in the Early Solar System Relies on Radioactive Isotopes
104(3)
4.4.1 Radiometric Dating Relies on the Exponential Decay of Radioisotopes
104(1)
4.4.2 Radiometric Dating Uses Isochron Plots
105(2)
4.5 Planetary Migration Is Required to Resolve Several Paradoxes
107(10)
4.5.1 Theories of Planetary Migration Have Been Derived
107(2)
4.5.1.1 Planets Embedded in a Gas Disc Experience Type I Migration
108(1)
4.5.1.2 Planets in Gaps Experience Type II Migration
108(1)
4.5.1.3 Halting Migration
108(1)
4.5.1.4 Gravitational Scattering
108(1)
4.5.2 Some Features of Solar System Architecture Have Been Hard to Explain
109(2)
4.5.2.1 The Late Heavy Bombardment (LHB) Is One Model of Impact History
109(2)
4.5.3 The Nice Model Accounts for Solar System Architecture by Planetary Migration
111(6)
4.5.3.1 Simulating the Early Solar System
111(1)
4.5.3.2 The Original Nice Model Explains the Eccentricities of the Giants
111(1)
4.5.3.3 The Nice Model Has an Explanation for the Late Heavy Bombardment
112(1)
4.5.3.4 The Main Asteroid Belt May Provide Clues to the Origin of the LHB
112(3)
4.5.3.5 The Grand Tack Accounts for the Inner Solar System
115(2)
5 Early Earth 117(40)
5.1 Assembly of the Earth Can Be Modeled
117(1)
5.1.1 To First Approximation Earth Grew at a Decreasing Exponential Rate
117(1)
5.1.2 Accretion Was Probably Heterogeneous
117(1)
5.2 Early Earth Was Shaped by a Moon-Forming Impact
117(6)
5.2.1 The Moon-Forming Impact Is Supported by Theory and Geochemistry
118(4)
5.2.1.1 Computer Simulations Show a Moon-Forming Impact Is Dynamically Feasible
118(1)
5.2.1.2 Much of Theia's Core Becomes Part of Earth's Core
119(1)
5.2.1.3 Lunar Rocks Are Depleted in Volatiles
119(1)
5.2.1.4 Earth and Moon Have the Same Oxygen and Silicon Isotopes
120(1)
5.2.1.5 The Moon May Have Originated from the Earth's Mantle after It Had Already Produced a Crust
121(1)
5.2.1.6 Changing Model Parameters Can Achieve Similar Isotopic Compositions for the Earth and Moon
121(1)
5.2.1.7 There Are Difficulties with the Giant Impact Theory
122(1)
5.2.2 The Timing of the Moon-Forming Impact Is Poorly Constrained
122(1)
5.2.3 Tidal Forces Drove Evolution of the Earth—Moon System
122(1)
5.3 The Early Hadean Was Hot
123(4)
5.3.1 Earth's Postimpact Atmosphere Was Largely Rock Vapor
123(1)
5.3.2 A Magma Ocean Remained After the Moon-Forming Impact
124(1)
5.3.3 The Hadean Mantle, Atmosphere, and Oceans Could Have Coevolved
124(2)
5.3.3.1 Early Hadean Earth Experienced a Runaway Greenhouse
125(1)
5.3.3.2 CO2 Must Have Been Removed from the Atmosphere
126(1)
5.3.4 A Dry Accreting Earth Would Be Hot During the Hadean
126(1)
5.4 Late Events Modified the Composition of the Earth
127(3)
5.4.1 Earth's Mantle and Crust Has an Excess of Siderophile Elements
127(1)
5.4.2 Core Separation Happened at High Pressure and Temperature
127(1)
5.4.3 Siderophile Elements Were Likely Delivered by a Late Veneer
128(1)
5.4.4 The Mantle Has Become More Oxidized with Time
128(2)
5.4.4.1 Degassing Oxidized the Upper Mantle
129(1)
5.4.4.2 Large Terrestrial Planets Self-Oxidize
129(1)
5.5 How Did the Terrestrial Planets Acquire Water?
130(5)
5.5.1 The Water Inventory of the Earth Is Not Well Known
130(1)
5.5.2 Did Terrestrial Planets Accrete Dry?
130(1)
5.5.3 Did Terrestrial Planets Accrete Wet?
131(2)
5.5.3.1 Formation of Hydrated Minerals In Situ Is Unlikely
131(1)
5.5.3.2 Influx of Wet Planetesimals Could Have Been Responsible for Wet Accretion
132(1)
5.5.4 Volatile Delivery Could Have Occurred Late
133(2)
5.5.4.1 Comets Are a Potential Source of Water
134(1)
5.5.4.2 Asteroids Are a Potential Source of Water
134(1)
5.5.4.3 Water Delivery May Have Been Stochastic
135(1)
5.6 The Temperature of the Late Hadean and Archaean Are Not Well Constrained
135(4)
5.6.1 Geological Clues Suggest Early Earth Was Warm Rather Than Hot
135(2)
5.6.2 When Did the First Oceans Form?
137(2)
5.6.2.1 Do Zircons Provide Evidence for Oceans by 4.4 Gyr?
137(1)
5.6.2.2 Water-Lain Sediments Are Found at 3.85 Gyr
138(1)
5.6.2.3 Evidence for Hydrothermal Activity Is Not Evidence for Oceans
138(1)
5.7 Plate Tectonics on Early Earth
139(4)
5.7.1 When Did Plate Tectonics Start on Earth?
139(1)
5.7.2 Plate Tectonics May Not Have Operated in the Hadean
139(1)
5.7.2.1 High Resurfacing in the Hadean May Have Led to Efficient Cooling
140(1)
5.7.3 What Was the Nature of Early Plate Tectonics?
140(3)
5.7.3.1 Most Continental Crust Formed in the Archaean
141(1)
5.7.3.2 The Style of Plate Tectonics Changed 3 Gyr Ago
142(1)
5.7.3.3 Vertical Tectonics May Have Generated the First Continental Crust
142(1)
5.8 Earth's Atmosphere Has Changed Over Time
143(14)
5.8.1 Earth's Atmosphere May Come from Two Sources
143(1)
5.8.2 The Oxidation State of The Atmosphere Has Altered
144(1)
5.8.3 Nitrogen May Be Derived from Ammonia
144(2)
5.8.4 The Faint Young Sun Paradox
146(11)
5.8.4.1 Lower Albedo Is a Controversial Solution to the Faint Young Sun Paradox
147(1)
5.8.4.2 Higher Amounts of Greenhouse Gases Could Solve the Faint Young Sun Paradox
147(3)
5.8.4.3 The Pressure of the Earth's Atmosphere Was Less Than Twice Its Present Value 2.7 Gyr Ago
150(2)
5.8.4.4 Carbon Dioxide Cannot Have Been Greater Than 0.03 Bar in the Late Archaean Atmosphere
152(1)
5.8.4.5 Model Late Archaean Atmospheres Can Keep Earth Warm
152(2)
5.8.4.6 There Are Several Abiotic Sources for Atmospheric Methane
154(1)
5.8.4.7 Is Abiotic Methane Sufficient to Solve the Faint Young Sun Paradox?
154(3)
6 Properties of Life 157(18)
6.1 Can Life Be Defined?
157(12)
6.1.1 Life Is a Complex, Self-Organizing, Adaptive Chemical System
157(1)
6.1.1.1 Complexity in Living Systems Is Hard to Define
157(1)
6.1.1.2 Living Systems Have Emergent Properties
157(1)
6.1.2 The Chemistry of Life Is Far from Equilibrium
158(4)
6.1.2.1 When Will a Reaction Happen Spontaneously?
159(2)
6.1.2.2 Life Obeys the Second Law of Thermodynamics
161(1)
6.1.2.3 Life Messes Up Its Environment
161(1)
6.1.3 Life Requires an Energy Source
162(5)
6.1.3.1 Solar Radiation Can Be Harnessed Directly by Photosynthesis
162(2)
6.1.3.2 Organic Carbon Is Oxidized in Respiration
164(1)
6.1.3.3 Redox Reactions Are Coupled Reduction-Oxidation Reactions
165(1)
6.1.3.4 Redox Reactions Are Quantified by Redox Potentials
165(2)
6.1.3.5 Are Redox Mechanisms a Universal Attribute for Life?
167(1)
6.1.4 Living Systems Are Capable of Self-Replication
167(1)
6.1.5 Life Exhibits Darwinian Evolution
167(2)
6.1.5.1 Evolution Has No Goal
168(1)
6.1.5.2 Complexity of Living Systems Tends to Increase with Time
168(1)
6.1.5.3 Is Darwinian Evolution Universal to Life Everywhere?
169(1)
6.1.6 How Useful Are These Criteria for Detecting Life?
169(1)
6.2 Are There Universal Chemical Requirements for All Life?
169(6)
6.2.1 No Element Is More Versatile in Its Chemistry Than Carbon
169(2)
6.2.1.1 Carbon Is Tetravalent
170(1)
6.2.1.2 Carbon Has a Moderate Electronegativity
170(1)
6.2.1.3 Can Silicon Substitute for Carbon in Biochemistry?
171(1)
6.2.2 Water As a Universal Solvent
171(4)
6.2.2.1 Alternative Solvents Have Been Postulated
172(3)
7 Terrestrial Biochemistry 175(34)
7.1 Building Blocks for Life
175(7)
7.1.1 Polymeric Macromolecules
175(7)
7.1.1.1 Polypeptides Are Polymers of Amino Acids
175(2)
7.1.1.2 Nucleic Acids Are Informational Macromolecules
177(2)
7.1.1.3 Polysaccharides Are Polymers of Sugars
179(1)
7.1.1.4 Lipids
179(3)
7.2 All Life on Earth Consists of Cells
182(6)
7.2.1 Information Flow in Cells
182(2)
7.2.1.1 Genes Have Several Components
183(1)
7.2.2 All Life on Earth Has One of Two Basic Cell Architectures
184(2)
7.2.2.1 Prokaryotes Have Simpler Genomes than Eukaryotes
184(1)
7.2.2.2 Eukaryotes Have Mitochondria and Chloroplasts
185(1)
7.2.2.3 All Cells Have Internal Scaffolding
185(1)
7.2.2.4 Almost All Organisms on Earth Are Prokaryotes
185(1)
7.2.3 Gene Transfer Can Occur Vertically or Horizontally
186(1)
7.2.4 All Life on Earth Falls into Three Domains
186(2)
7.3 DNA Is the Universal Replicator
188(5)
7.3.1 All Life on Earth Uses DNA
188(1)
7.3.2 DNA Replication Was Deduced from Theory
188(1)
7.3.3 DNA Acts as a Template
189(4)
7.3.3.1 DNA Replication Is Fast
189(2)
7.3.3.2 DNA Replication Requires Catalysts
191(1)
7.3.3.3 DNA Replication Is High Fidelity
191(1)
7.3.3.4 DNA Mutations Are the Source of Variation
191(1)
7.3.3.5 The Genetic Code Shows a Single Origin of All Life
191(1)
7.3.3.6 The Genetic Code Provides Clues to Its Origin
192(1)
7.4 Metabolism Matches Lifestyle
193(3)
7.4.1 Living Systems Enhance Reaction Kinetics
194(1)
7.4.2 Life on Earth Has Three Metabolic Requirements
195(1)
7.4.2.1 Organisms Can Be Categorized by Metabolism
195(1)
7.5 Cells Harness Free Energy
196(9)
7.5.1 Respiration Requires an Exogenous Electron Acceptor
196(1)
7.5.2 Most Carbon Oxidation Happens in the Krebs Cycle
196(2)
7.5.3 Electron Chains "Quantize" Free Energy Availability
198(1)
7.5.4 AG" of Redox Reactions Can Be Calculated
198(2)
7.5.4.1 Exergonic Reactions Have Positive A g
198(2)
7.5.5 Proton Gradients Are the Core of Terrestrial Metabolism
200(2)
7.5.5.1 Prokaryotes Pump Proteins Across Their Cell Membrane
200(1)
7.5.5.2 Eukaryotes Make ATP in Mitochondria
200(2)
7.5.5.3 Electron Transport Uses Metal Ions
202(1)
7.5.6 Anerobic Respiration Uses Electron Acceptors Other Than Oxygen
202(2)
7.5.7 Fermentation Uses an Endogenous Electron Acceptor
204(1)
7.6 Phototrophs Harvest Sunlight
205(1)
7.6.1 Not All Photosynthesis Produces Oxygen
205(1)
7.6.2 Oxygenic Photosynthesis Produces ATP and Reducing Power
205(1)
7.7 Prokaryotes Live in the Crust
206(3)
7.7.1 Crust Provides an Ecologic Niche
206(1)
7.7.2 Chemolithotrophs "Eat" Rock
207(2)
8 Origin of Life 209(26)
8.1 When Did Life Originate?
209(5)
8.1.1 When Did Earth Become Cool Enough for Life?
209(1)
8.1.2 Evidence for Early Life
209(3)
8.1.2.1 Do Light Carbon Isotopes Hint at First Life?
210(2)
8.1.2.2 Fossils or Artifacts?
212(1)
8.1.3 Precambrian Life Was Dominated by Stromatolites
212(2)
8.2 Building the Molecules of Life
214(9)
8.2.1 Where Did Prebiotic Synthesis Happen?
214(4)
8.2.1.1 Urey—Miller Experiments Have a Fatal Flaw
215(1)
8.2.1.2 Carbonaceous Chondrites Are Rich in Organics
216(1)
8.2.1.3 Most Organic Carbon in Meteorites and Comets Is Unavailable
217(1)
8.2.2 Did Replication Precede Metabolism?
218(5)
8.2.2.1 Did Life Begin with a Self-Copying Molecule?
218(1)
8.2.2.2 Ribozymes Support an RNA World
218(1)
8.2.2.3 Evidence for the RNA World
219(1)
8.2.2.4 Making Ribonucleosides Is a Problem
220(1)
8.2.2.5 Pyrimidine Ribonucleotide Synthesis Can Happen Under Prebiotic Conditions
220(1)
8.2.2.6 Abiotic Synthesis of Self-Replicating RNA Is a Problem
220(1)
8.2.2.7 Was There a Pre-RNA Replicator?
221(1)
8.2.2.8 Why the RNA World Idea Might Be Wrong
222(1)
8.2.3 Did Metabolism Emerge Before Replication?
223(1)
8.3 How Did Life Originate?
223(12)
8.3.1 What Were the First Organisms?
224(1)
8.3.2 What Was the Last Universal Common Ancestor?
224(1)
8.3.2.1 LUCA Lacked Several Traits
225(1)
8.3.2.2 LUCA Was a Hyperthermophile
225(1)
8.3.3 Hydrothermal Vents Are Prime Candidates for Genesis
225(10)
8.3.3.1 Black Smokers Are Acidic Hydrothermal Vents
226(1)
8.3.3.2 Acidic Vents Were Initially Proposed for Life's Origin
226(1)
8.3.3.3 Alkaline Vents Are More Favorable Cradles Than Acidic Vents
227(1)
8.3.3.4 Serpentinization Makes Hydrogen and Methane
228(1)
8.3.3.5 Alkaline Vents Can Provide Energy for Life
229(1)
8.3.3.6 Did the First Metabolic Pathway Reduce CO2 with H2 to Produce Acetate?
229(2)
8.3.3.7 Alkaline Vents Have Proton Gradients
231(1)
8.3.3.8 Did the First Pathway Make Acetyl Phosphate?
231(1)
8.3.3.9 Temperature Gradients Encourage Polymerization
232(1)
8.3.3.10 DNA, RNA, and Proteins Evolved in the Vent
232(3)
9 Early Life 235(20)
9.1 A Methane Greenhouse
235(1)
9.1.1 A Shift from CO2 to CH4 Greenhouse Happened in the Late Archaean
235(1)
9.1.2 An Organic Haze Would Form as CH4 Levels Rose
235(1)
9.2 The Great Oxidation Event
236(4)
9.2.1 The Oxygen Source Was Photosynthesis
236(1)
9.2.2 Evidence for the GOE is Geochemical
237(3)
9.2.2.1 Sulfur Isotopes Time the GOE
237(1)
9.2.2.2 Banded Iron Formations: A Red Herring?
238(2)
9.2.3 Whiffs of Oxygen Preceded the GOE
240(1)
9.2.4 Glaciations Coincided with the GOE
240(1)
9.3 The "Boring Billion"
240(4)
9.3.1 O2 Levels Plummeted After the GOE
241(1)
9.3.2 The Canfield Ocean Is Anoxic and Sulfidic
241(2)
9.3.2.1 Euxinia Locks Up Essential Trace Metals
243(1)
9.3.3 The Neoproterozoic Oxidation Event
243(1)
9.3.3.1 Oxidation Produced Glaciation
243(1)
9.3.3.2 Continent Configuration Contributed to the Freeze
243(1)
9.4 The Emergence of Life
244(3)
9.4.1 Methanogenesis and Sulfate Reduction Were Intertwined
244(1)
9.4.2 Nitrogen Fixation Probably Evolved Very Early
244(1)
9.4.3 Genome Expansion Occurred in the Archaean
245(1)
9.4.4 When Did Oxygenic Photosynthesis Start?
246(1)
9.4.4.1 Anoxygenic Photosynthesis Evolved First
246(1)
9.4.4.2 12C, BIFs, and Cyanobacterial Biomarkers Are Red Herrings
247(1)
9.4.4.3 Did Oxygenic Photosynthesis Start 2.4 Gyr ago?
247(1)
9.5 Eukaryotes: Complex Life
247(7)
9.5.1 When Did Eukaryotes Appear?
247(1)
9.5.2 Eukaryotes Are Archaeon-Bacteria Chimeras
248(1)
9.5.2.1 Endosymbiotic Origin for Eukaryotes Is a Nineteenth Century Idea
248(1)
9.5.2.2 Eukarya Only Evolved Once
248(1)
9.5.3 The Hydrogen Hypothesis Explains Endosymbiosis
249(2)
9.5.3.1 Symbiosis Is a Two-Way Exchange
249(2)
9.5.3.2 Symbiosis Had to Be Rapid
251(1)
9.5.3.3 Mitochondria Lost Genes to the Nucleus
251(1)
9.5.4 Eukaryotes Inherited Bacterial Lipids
251(1)
9.5.5 Eukaryotes Have Huge Advantages Over Prokaryotes
251(1)
9.5.5.1 Prokaryotes with Small Genomes Are Favored
252(1)
9.5.5.2 Small Is Best for Energy Efficiency
252(1)
9.5.6 Mitochondria Are Advantageous for Energetics
252(1)
9.5.6.1 Oxidative Phosphorylation Is Normally Demand Led
253(1)
9.5.6.2 Oxidative Phosphorylation Can Be Supply Led
253(1)
9.5.7 Large Size Is Advantageous for Eukaryotes
253(1)
9.6 The Fate of Life on Earth
254(1)
9.6.1 Earth Will Be Habitable for Another 1.5 Billion Years
254(1)
10 Mars 255(34)
10.1 Martian Romance
255(1)
10.1.1 Mariner Missions Reveal a Cold Arid World
255(1)
10.2 Martian Geology
255(9)
10.2.1 Mars Is a Planetary Embryo
255(2)
10.2.1.1 The Martian Core Is Totally or Partly Liquid
256(1)
10.2.1.2 When Mars Lost Its Magnetic Field Is Significant
256(1)
10.2.2 Mars Has Two Very Different Hemispheres
257(3)
10.2.2.1 The Origin of the Northern Lowlands Is Uncertain
257(1)
10.2.2.2 The Tharsis Bulge Is the Highest Region on Mars
257(2)
10.2.2.3 Cratering Rates Provide Clues to Mars' History
259(1)
10.2.3 Spectrometry Reveals the Nature of Planetary Surfaces
260(3)
10.2.3.1 Gamma Ray Spectrometry (GRS)
260(1)
10.2.3.2 Alpha-Particle-X-Ray Spectrometry (APXS)
261(1)
10.2.3.3 Thermal Emission Spectrometry (TES)
261(1)
10.2.3.4 Reflectance Spectrometry
262(1)
10.2.3.5 X-Ray Diffraction (XRD)
262(1)
10.2.4 The Martian Crust Is Mostly Basalt
263(1)
10.2.4.1 Much of the Surface of Mars Is Covered by Regolith
264(1)
10.3 Water Ice Is Abundant on Mars
264(3)
10.3.1 Mars Has Substantial Frozen Water
264(3)
10.3.1.1 Obliquity Swings Redistribute Water Ice
264(1)
10.3.1.2 Subsurface Water Ice Is Revealed by Geological Features
265(1)
10.3.1.3 Subsurface Water Ice Has Been Detected by Geophysics
265(1)
10.3.1.4 Water Ice Has Been Seen Directly
265(2)
10.3.1.5 The Cryosphere Is a Thick Permafrost Layer
267(1)
10.3.1.6 Extensive Groundwater Aquifers Are Missing
267(1)
10.4 Water Has Flowed on Mars
267(8)
10.4.1 Mars Has Numerous Fluvial Features
268(2)
10.4.1.1 Valley Networks Are Not Like Terrestrial River Beds
268(1)
10.4.1.2 Outflow Channels Were Formed by Episodic Floods
268(1)
10.4.1.3 Did Early Mars Have a Northern Ocean?
269(1)
10.4.1.4 Martian Gulleys Are Enigmatic
270(1)
10.4.2 Mars Exploration Rovers Have Searched for Signs of Liquid Water
270(1)
10.4.2.1 Water Interaction at Gusev Has Been Limited
270(1)
10.4.2.2 Meridiani Hosts Water-Formed Minerals
270(1)
10.4.2.3 Was Meridiani Plain a Sulfate Brine Lake?
271(1)
10.4.3 Global Geological Markers Can Reveal How Long Mars Was Wet
271(3)
10.4.3.1 Lack of Carbonates Is a Red Herring
272(1)
10.4.3.2 The Martian Surface Has Not Suffered Much Alteration by Water
272(1)
10.4.3.3 Clays Provide Insight into Water Action
272(1)
10.4.3.4 Martian Clays Are Generally Noachian
272(1)
10.4.3.5 Much Hydrothermal Activity Was Produced by Impacts on Early Mars
273(1)
10.4.4 Mars Has Experienced Three Climates
274(1)
10.4.4.1 Clays Formed in the Phyllocian Era
274(1)
10.4.4.2 Sulfates Were Produced in the Theiikian Era
275(1)
10.4.4.3 The Siderikan Era Made Mars Red
275(1)
10.5 Atmosphere
275(9)
10.5.1 Liquid Water Cannot Exist at the Martian Surface Today
276(1)
10.5.2 Detection of Methane in the Martian Atmosphere Is Dubious
276(1)
10.5.3 Atmosphere of Early Mars
276(6)
10.5.3.1 Mars Probably Lost Most of Its Water Early On
277(1)
10.5.3.2 Mars Probably Lost Most of Its Atmosphere Early On
277(1)
10.5.3.3 Several Atmosphere Loss Mechanisms Likely Operated on Mars
277(1)
10.5.3.4 Impacts Can Remove Substantial Amounts of Atmosphere
277(1)
10.5.3.5 Sputtering Mass Fractionates Isotopes
278(1)
10.5.3.6 What Was the Atmospheric Pressure of Early Mars?
279(1)
10.5.3.7 Early Mars Probably Had a Reduced Atmosphere
280(1)
10.5.3.8 Climate Models Struggle to Warm Early Mars
280(2)
10.5.3.9 Hydrogen Might "Rescue" a Warm Climate
282(1)
10.5.4 Was Mars Episodically Warm and Wet?
282(2)
10.5.4.1 Can Impact Precipitation Account for the Fluvial Features'?
284(1)
10.6 Mars and Life
284(5)
10.6.1 The Viking Experiments Were Designed to Detect Life
284(2)
10.6.1.1 Pyrolytic Release Tests for Carbon Fixation
284(1)
10.6.1.2 Labeled Release (LR) Tests for Metabolism
285(1)
10.6.1.3 GCMS Detects Organic Compounds
285(1)
10.6.1.4 What Was the Legacy of Viking?
285(1)
10.6.2 Does ALH84001 Harbor Evidence of Life?
286(1)
10.6.2.1 ALH84001 Has Had a Shocking History
286(1)
10.6.2.2 Four Features Hinted at Relic Life
286(1)
10.6.2.3 Complex Organic Molecules Were Detected
286(1)
10.6.2.4 Iron Sulfide (Fe(II)S) and Iron Oxides Appeared Together
287(1)
10.6.2.5 Magnetite Crystals Are Enigmatic
287(1)
10.6.2.6 "Fossil Bacteria" Seem Too Small
287(1)
10.6.2.7 ALH84001 Does Not Provide Evidence for Life
287(1)
10.6.3 Martian Life Could Be Based on Iron and Sulfur Metabolism
287(2)
10.6.3.1 Terrestrial Iron-Oxidizing Bacteria "Breathe" Nitrate
287(1)
10.6.3.2 Mars Is Rich in Electron Acceptors for Fe- and S-Reduction
288(1)
11 Icy Worlds 289(32)
11.1 Life Might Exist Beyond the Conventional Habitable Zone
289(1)
11.2 Titan
289(14)
11.2.1 Titan Has a Dense Atmosphere
290(5)
11.2.1.1 A Methane Cycle Operates on Titan
290(2)
11.2.1.2 Titan Is an Ice—Silicate World
292(1)
11.2.1.3 Titan Harbors a Subsurface Water Ocean
293(1)
11.2.1.4 Ammonia Is an Anti-Freeze
294(1)
11.2.2 Atmospheric Methane Must Be Continually Regenerated
295(2)
11.2.2.1 Subsurface Methane Reservoirs Must Exist
295(1)
11.2.2.2 Why the Ocean Cannot Be the Source of Atmospheric Methane
296(1)
11.2.2.3 Cryovolcanism
296(1)
11.2.3 Organic Chemistry Occurs in Titan's Atmosphere
297(4)
11.2.3.1 Low Temperatures Make for Slow Kinetics
297(1)
11.2.3.2 Free Radical and Ion-Neutral Chemistry Dominates
298(1)
11.2.3.3 Methane Is the Precursor Hydrocarbon
299(1)
11.2.3.4 Nitrogen Leads to Nitriles
300(1)
11.2.3.5 Tholins Are Formed by Ion-Neutral Reactions
300(1)
11.2.3.6 Titan Chemistry Is Being Explored in the Laboratory
301(1)
11.2.4 Could There Be Life on Titan?
301(2)
11.2.4.1 Is the Subsurface Ocean Habitable?
301(1)
11.2.4.2 Terrestrial-Style Methanogenesis Is Dubious
302(1)
11.2.4.3 Titan's Atmosphere Poses Paradoxes
302(1)
11.3 Enceladus
303(5)
11.3.1 Enceladus Has Been Resurfaced Multiple Times
304(1)
11.3.2 Enceladus Cryovolcanic Plumes Contain Water Vapor
304(2)
11.3.3 What Heats Enceladus Now?
306(2)
11.3.3.1 Tidal Stresses Control Eruptions
307(1)
11.3.3.2 Cryovolcanism Is Probably Driven by Ammonia—Water Magma
308(1)
11.3.3.3 Putative Organisms Are Water-Based
308(1)
11.4 Europa
308(13)
11.4.1 Europa Is a Differentiated World
309(1)
11.4.2 There Is Good Evidence for a Europan Ocean
310(1)
11.4.3 How Thick Is the Europan Crust?
310(3)
11.4.3.1 Europa Experiences Tidal Heating
311(1)
11.4.3.2 Crustal Thickness Can Be Estimated from Mechanical Properties
312(1)
11.4.3.3 Surface Features Are Evidence for an Ocean
312(1)
11.4.3.4 Chaos Terrain Implies a Thin Crust
312(1)
11.4.3.5 Water—Ice Cryovolcanism May Occur on Europa
313(1)
11.4.4 The Europan Surface Is Chemically Altered
313(4)
11.4.4.1 Europa's Surface Is Altered by Radiolysis
314(1)
11.4.4.2 The Europan Ocean May Resemble Earth's Oceans
315(1)
11.4.4.3 Low Hydrogen Peroxide Abundance May Limit Oxidation of the Ocean
316(1)
11.4.4.4 How Effectively Do the Surface and Ocean Communicate?
316(1)
11.4.5 What Is the Astrobiological Potential of Europa?
317(4)
11.4.5.1 A Reducing Ocean Would Be a Sink for Oxidants
317(1)
11.4.5.2 Could H202 Support Biology?
318(1)
11.4.5.3 Energy for Hydrothermal Vents
318(1)
11.4.5.4 What Is the Oxidation State of the Europa Mantle?
319(2)
12 Detecting Exoplanets 321(22)
12.1 Exoplanet Bonanza
321(1)
12.1.1 The First Exoplanets Were Found by Timing Pulsars
321(1)
12.1.2 The First Exoplanet Around a Main Sequence Star Was Discovered in 1995
321(1)
12.2 Some Exoplanets Can Be Imaged Directly
322(2)
12.2.1 Planets Are Extremely Dim Compared to Their Host Stars
322(1)
12.2.2 Coronagraphs Create Artificial Eclipses
323(1)
12.2.3 Nulling Interferometry Cuts Out Starlight
323(1)
12.2.4 Direct Imaging Reveals High Mass Planets
323(1)
12.3 Astrometry Detects Binary Systems by Stellar "Wobble"
324(1)
12.4 The Radial Velocity Method Uses the Doppler Effect
325(6)
12.4.1 Defining the Radial Velocity
326(1)
12.4.1.1 Determining Radial Velocity Is a Challenge
326(1)
12.4.1.2 RV Calculations Must Sidestep the Unknown Inclination
326(1)
12.4.2 Finding the Period and Semi-Major Axis of an Exoplanet's Orbit
327(1)
12.4.3 The RV Method Provides a Lower Bound on Planetary Mass
328(1)
12.4.4 The RV Method Is Biased to Detect Massive Planets with Short Periods
329(2)
12.5 Exoplanets Are Revealed When They Transit Their Star
331(8)
12.5.1 Exoplanet Transits Dim Starlight
331(2)
12.5.2 The Transit Method Allows Several Parameters to Be Deduced
333(4)
12.5.2.1 The Period Gives the Semi-Major Axis of the Exoplanet's Orbit
333(1)
12.5.2.2 Transits Allow Mass to Be Refined
334(2)
12.5.2.3 Exoplanet Radius, Volume, and Bulk Density Can Be Found
336(1)
12.5.2.4 Exoplanetary Temperature and Atmosphere Composition May Be Revealed
336(1)
12.5.2.5 Exoplanet Albedo Can Be Estimated
336(1)
12.5.2.6 False Positives Arise with the Transit Method
336(1)
12.5.3 Transit Timing Variation Uncovers Multiple and Circumbinary Exoplanets
337(1)
12.5.4 Transits Can Potentially Detect Earth-Mass Planets
337(1)
12.5.5 Most Transit Detections Have Been Made from Space
338(1)
12.5.5.1 Kepler Had 961 Confirmed Exoplanets by April 2014
338(1)
12.6 Gravitational Lensing Can Unveil Exoplanets
339(2)
12.6.1 Gravitational Microlensing Events Are Short-Lived
339(1)
12.6.2 Microlensing Yields Information About Exoplanet Systems
339(2)
12.6.3 There Are Both Pros and Cons to Lensing
341(1)
12.7 Detection Methods Are Biased
341(2)
12.7.1 Survey Statistics Can Estimate What We Cannot Detect
342(1)
13 Exoplanetary Systems 343(34)
13.1 Surveys Probe Exoplanet Properties
343(6)
13.1.1 Exoplanet Diversity Is Large
343(1)
13.1.2 Exoplanets Are Classified According to Their Size
343(2)
13.1.3 Hot Jupiters Were Discovered Early
345(1)
13.1.4 Small Exoplanets Are Commonest
345(1)
13.1.4.1 The Planet/Star Ratio Is of Order One
346(1)
13.1.5 Exoplanet Composition Can Sometimes Be Deduced
346(3)
13.1.5.1 Compositions Can Be Plotted on a Ternary Diagram
346(2)
13.1.5.2 Protoplanets with Mass Greater than 1.5M® May Become Mini-Neptunes
348(1)
13.1.5.3 Could Water Worlds Exist?
349(1)
13.1.5.4 How Big Must a Planet Be to Have Plate Tectonics?
349(1)
13.1.6 Exoplanet Temperature Can Be Estimated
349(1)
13.2 Exoplanet Host Star Properties
349(2)
13.2.1 Metal-Rich Stars Are More Likely to Host Gas Giants
349(1)
13.2.2 Did Terrestrial Planets Form 11 Billion Years Ago?
350(1)
13.2.3 Most Stars with Planets Have Low Lithium Abundance
350(1)
13.3 Habitable Exoplanets
351(15)
13.3.1 II® Is the Proportion of Stars with Habitable Planets
351(1)
13.3.2 An Earth-Sized Planet in the Habitable Zone Has Been Discovered
351(1)
13.3.3 How to Define a Habitable Zone
352(3)
13.3.3.1 Conservative HZ
352(1)
13.3.3.2 Optimistic HZ
352(1)
13.3.3.3 HZ Location Varies with Stellar Temperature
353(1)
13.3.3.4 Desert Worlds Can Be Very Close to Their Host Stars
353(1)
13.3.3.5 Three-Dimensional Climate Models Are Needed
353(1)
13.3.3.6 The HZ Depends on the Planetary Mass
354(1)
13.3.3.7 Is a Planet in the HZ?
354(1)
13.3.4 Has Been Derived from Kepler Data
355(1)
13.3.5 Habitable Planets Around M-Dwarfs?
355(2)
13.3.5.1 Habitable Planets Around M-Dwarfs May Be Tidally Locked
356(1)
13.3.5.2 M-Dwarf Radiation Could Be Problematic
357(1)
13.3.5.3 Red Dwarf Magnetic Fields Are Problematic
357(1)
13.3.5.4 Planets Around M-Dwarfs Are Probably Water-Depleted
357(1)
13.3.6 Eccentric Orbits Influence Exoplanet Habitability
357(4)
13.3.6.1 Giant Planets Can Clear Out the Habitable Zone
358(1)
13.3.6.2 Can Life Survive on Worlds in Eccentric Orbits?
359(2)
13.3.7 Planets Exist in Binary Systems
361(5)
13.3.7.1 S Orbits Are Possible for Close Binaries
361(1)
13.3.7.2 Habitable Planets Probably Exist in Binary Systems
361(2)
13.3.7.3 Circumbinary Planets Have Been Identified
363(3)
13.4 The Galactic and Habitability
366(11)
13.4.1 The Milky Way Is a Spiral Galaxy
366(1)
13.4.2 Galactic Chemistry Influences Habitability
366(1)
13.4.3 The Galaxy Has a Habitable Zone
367(2)
13.4.3.1 Low Metallicity Chokes Planet Accretion
367(1)
13.4.3.2 The Galactic Center Is Dangerous
368(1)
13.4.3.3 The Boundary of the GHZ Has Been Defined
369(1)
13.4.4 Are There Habitable Planets in Clusters?
369(1)
13.4.4.1 Globular Clusters Are Probably Barren
369(1)
13.4.4.2 Open Clusters Likely Harbor Planets
370(1)
13.4.5 Biosignatures
370(7)
13.4.5.1 Earth Provides Practice in Acquiring Biosignatures
370(2)
13.4.5.2 Atmosphere Spectra Have Been Obtained
372(1)
13.4.5.3 Water Need Not Mean Habitability
372(1)
13.4.5.4 Some Biosignature Gases Are Produced by Metabolism
373(1)
13.4.5.5 The Red Edge Is a Relatively Unambiguous Biosignature
374(1)
13.4.5.6 Time-Varying Signatures Could Indicate Habitability
375(2)
14 Prospecting for Life 377(22)
14.1 Rare Earth versus the Principle of Mediocrity
377(6)
14.1.1 Is an Early Origin a Guide to the Probability of Life?
377(3)
14.1.1.1 Earth Is Not a Randomly Selected System
377(1)
14.1.1.2 If Biogenesis Is a Lottery It Is Likely
378(1)
14.1.1.3 If We Account for Selection Effects Biogenesis Is Rare
378(2)
14.1.2 Life May Be Rare or Common in the Galaxy
380(1)
14.1.3 Several Hard Steps Could Be Needed for Intelligent Observers to Emerge
381(1)
14.1.3.1 How Many Steps Are Needed?
381(1)
14.1.4 What Are the Hard Steps?
382(1)
14.1.4.1 Several Hard Step Sequences Have Been Proposed
382(1)
14.1.4.2 Unique Events Are Presumably the Hardest
383(1)
14.1.4.3 Some Events May Have Happened Only Once
383(1)
14.1.4.4 Is Intelligence with Language Sufficient?
383(1)
14.2 Is Life Seeded from Space?
383(6)
14.2.1 Survival of Ancient Bacteria Makes Panspermia Plausible
384(1)
14.2.2 Life May Be Uncommon Despite Panspermia
384(1)
14.2.3 Radiation Is a Major Hazard
385(2)
14.2.3.1 Some Bacteria Have High Radioresistance
385(1)
14.2.3.2 Experiments Have Revealed Limits to Survival in Space
386(1)
14.2.4 Can Micro-Organisms Survive Lithopanspermia?
387(2)
14.2.4.1 Extremophiles Can Survive High Accelerations
387(1)
14.2.4.2 Are We All Martians?
387(2)
14.3 Metrics for Extraterrestrials
389(3)
14.3.1 Is the Drake Equation More Than a Guess?
389(2)
14.3.2 Alternatives to the Drake Equation Have Been Developed
391(1)
14.4 SETI and the Fermi Paradox
392(7)
14.4.1 Radio SETI
393(1)
14.4.2 Optical SETI
393(2)
14.4.3 How Far Away Would Passive Radiation Reveal Our Presence?
395(1)
14.4.4 Where Is Everybody?
396(3)
14.4.4.1 SETI Has Not Been Long or Far-Reaching Enough
397(1)
14.4.4.2 Extraterrestrial Civilizations May Be Widely Separated in Time
397(1)
14.4.4.3 Extraterrestrial Civilizations Are Widely Separated in Space
397(1)
14.4.4.4 Are There Resource Constraints on Interstellar Travel?
398(1)
14.4.4.5 Are Extraterrestrial Civilizations Intrinsically Rare?
398(1)
Bibliography 399(8)
Index 407
Alan Longstaff originally trained as a biochemist and, after a senior lectureship in the Biosciences Department at the University of Hertfordshire, he became a university student once again to study astronomy and planetary science. He now divides his time between teaching and writing. Since 2003, he has worked part-time as an astronomy tutor and planetarium presenter for The Royal Observatory, Greenwich, and held part-time teaching posts at Queen Mary University of London, Waldegrave Science School for Girls, and the Open University. He has lectured to astronomical and geological societies, co/authored several textbooks, and is a regular contributor to Astronomy Now.
Biežāk uzdotie jautājumi par e-grāmatām Biežāk uzdotie jautājumi par e-grāmatām
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