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.
Table of Contents
Origin of the Elements
Elements for Life
The Universe Started from a Hot and Dense State
Abundances of Primordial Elements Are Predicted by the Big Bang Hypothesis
The Message of Light
Atoms and Molecules Process Electromagnetic Radiation
Electronic Transitions Are Quantized
Energy Levels Govern Electronic Transitions in the Hydrogen Atom
Spectrographs Are Used to Capture Spectra
Stellar Spectra Encode Temperature and Elemental Abundances
The Properties of Main Sequence Stars Are Determined by Their Masses
Stars Form by the Collapse of Giant Molecular Clouds
Protostars Contract Down Onto the Main Sequence
Main Sequence Stars Fuse Hydrogen to Helium
Many Low Mass Stars Become Red Giants
High Mass Stars Make High Mass Elements
The Chemistry of Space
From Elements to Molecules
Cool Stars Have Molecular Absorption Lines
The Interstellar Medium Is Extremely Tenuous
The ISM Contains Dust Grains
AGB Stars Have Either Oxygen- or Carbon-Rich Atmospheres
Doing Chemistry in Space
Different Chemistry Operates in Dense Clouds and Diffuse Clouds
Molecules Are Detected Mostly by Vibrational and Rotational Spectra
Molecules in the ISM
Dust Grain Surfaces Catalyze Synthesis of Hydrogen Molecules
Chemical Species Can Trace ISM Conditions and Processes
Earth in Context
There Are Eight Major Planets
The Planets Were Condensed from a Spinning Disc
The Solar System Contains Numerous Small Bodies
What Is a Planet?
Habitability Is an Attribute of the Entire Earth System
The Structure and Composition of the Solid Earth
The Chondritic Earth Model Provides a First Approximation to Its Bulk Composition
Seismology Provides a Picture of the Earth’s Interior
What Makes Earth Habitable?
Temperature at the Earth’s Surface Is Largely Determined by the Sun
Liquid Water Exists on the Earth’s Surface
Earth Is in a Stable Orbit in the Habitable Zone
Earth’s Dense Atmosphere Contributes to Habitability
A Global Magnetic Field May Be Required for Habitability
Earth Seems Unique in Having Plate Tectonics
Plate Tectonics Depends on a Weak Mantle Layer
New Ocean Crust Is Made at Constructive Plate Boundaries
Ocean Crust Is Destroyed at Destructive Plate Boundaries
Hot Spot Volcanism: Evidence for Mantle Convection?
Plate Tectonics Is Self-Regulating
Plate Tectonics May Be Required for Habitability
Plate Tectonics Seems Not to Operate on Mars or Venus
Building the Solar System
Planet Formation Is Contingent
Planets Formed by Accretion from the Solar Nebula
The Solar Nebula Was a Dynamic Environment
The Solar Nebula Formed a Spinning Disc
Planet and Star Formation Occur Together
Condensation of Solids from the Solar Nebula Depended on Temperature
Accretion Involves Several Distinct Mechanisms
Heat Sources Drive Differentiation
Differentiation Redistributes Elements
Gas Giants Must Have Assembled Within a Few Million Years
Accretion of Terrestrial Planets Took Tens of Millions of Years
The Solar System Started with a Bang
26Mg Traces the Original 26Al
Did the Decay of 26Al Make Life on Earth Possible?
Dating Events in the Early Solar System Relies on Radioactive Isotopes
Radiometric Dating Relies on the Exponential Decay of Radioisotopes
Radiometric Dating Uses Isochron Plots
Planetary Migration Is Required to Resolve Several Paradoxes
Theories of Planetary Migration Have Been Derived
Some Features of Solar System Architecture Have Been Hard to Explain
The Nice Model Accounts for Solar System Architecture by Planetary Migration
Assembly of the Earth Can Be Modeled
To First Approximation Earth Grew at a Decreasing Exponential Rate
Accretion Was Probably Heterogeneous
Early Earth Was Shaped by a Moon-Forming Impact
The Moon-Forming Impact Is Supported by Theory and Geochemistry
The Timing of the Moon-Forming Impact Is Poorly Constrained
Tidal Forces Drove Evolution of the Earth–Moon System
The Early Hadean Was Hot
Earth’s Postimpact Atmosphere Was Largely Rock Vapor
A Magma Ocean Remained After the Moon-Forming Impact
The Hadean Mantle, Atmosphere, and Oceans Could Have Coevolved
A Dry Accreting Earth Would Be Hot During the Hadean
Late Events Modified the Composition of the Earth
Earth’s Mantle and Crust Has an Excess of Siderophile Elements
Core Separation Happened at High Pressure and Temperature
Siderophile Elements Were Likely Delivered by a Late Veneer
The Mantle Has Become More Oxidized with Time
How Did the Terrestrial Planets Acquire Water?
The Water Inventory of the Earth Is Not Well Known
Did Terrestrial Planets Accrete Dry?
Did Terrestrial Planets Accrete Wet?
Volatile Delivery Could Have Occurred Late
The Temperature of the Late Hadean and Archaean Are Not Well Constrained
Geological Clues Suggest Early Earth Was Warm Rather Than Hot
When Did the First Oceans Form?
Plate Tectonics on Early Earth
When Did Plate Tectonics Start on Earth?
Plate Tectonics May Not Have Operated in the Hadean
What Was the Nature of Early Plate Tectonics?
Earth’s Atmosphere Has Changed over Time
Earth’s Atmosphere May Come from Two Sources
The Oxidation State of the Atmosphere Has Altered
Nitrogen May Be Derived from Ammonia
The Faint Young Sun Paradox
Properties of Life
Can Life Be Defined?
Life Is a Complex, Self-Organizing, Adaptive Chemical System
The Chemistry of Life Is Far from Equilibrium
Life Requires an Energy Source
Living Systems Are Capable of Self-Replication
Life Exhibits Darwinian Evolution
How Useful Are These Criteria for Detecting Life?
Are There Universal Chemical Requirements for All Life?
No Element Is More Versatile in Its Chemistry than Carbon
Water as a Universal Solvent
Building Blocks for Life
All Life on Earth Consists of Cells
Information Flow in Cells
All Life on Earth Has One of Two Basic Cell Architectures
Gene Transfer Can Occur Vertically or Horizontally
All Life on Earth Falls into Three Domains
DNA Is the Universal Replicator
All Life on Earth Uses DNA
DNA Replication Was Deduced from Theory
DNA Acts as a Template
Metabolism Matches Lifestyle
Living Systems Enhance Reaction Kinetics
Life on Earth Has Three Metabolic Requirements
Cells Harness Free Energy
Respiration Requires an Exogenous Electron Acceptor
Most Carbon Oxidation Happens in the Krebs Cycle
Electron Chains "Quantize" Free Energy Availability
ΔG°′ of Redox Reactions Can Be Calculated
Proton Gradients Are the Core of Terrestrial Metabolism
Anerobic Respiration Uses Electron Acceptors Other Than Oxygen
Fermentation Uses an Endogenous Electron Acceptor
Phototrophs Harvest Sunlight
Not All Photosynthesis Produces Oxygen
Oxygenic Photosynthesis Produces ATP and Reducing Power
Prokaryotes Live in the Crust
Crust Provides an Ecologic Niche
Chemolithotrophs "Eat" Rock
Origin of Life
When Did Life Originate?
When Did Earth Become Cool Enough for Life?
Evidence for Early Life
Precambrian Life Was Dominated by Stromatolites
Building the Molecules of Life
Where Did Prebiotic Synthesis Happen?
Did Replication Precede Metabolism?
Did Metabolism Emerge Before Replication?
How Did Life Originate?
What Were the First Organisms?
What Was the Last Universal Common Ancestor?
Hydrothermal Vents Are Prime Candidates for Genesis
A Methane Greenhouse
A Shift from CO2 to CH4 Greenhouse Happened in the Late Archaean
An Organic Haze Would Form as CH4 Levels Rose
The Great Oxidation Event
The Oxygen Source Was Photosynthesis
Evidence for the GOE is Geochemical
Whiffs of Oxygen Preceded the GOE
Glaciations Coincided with the GOE
The "Boring Billion"
O2 Levels Plummeted After the GOE
The Canfield Ocean Is Anoxic and Sulfidic
The Neoproterozoic Oxidation Event
The Emergence of Life
Methanogenesis and Sulfate Reduction Were Intertwined
Nitrogen Fixation Probably Evolved Very Early
Genome Expansion Occurred in the Archaean
When Did Oxygenic Photosynthesis Start?
Eukaryotes: Complex Life
When Did Eukaryotes Appear?
Eukaryotes Are Archaeon–Bacteria Chimeras
The Hydrogen Hypothesis Explains Endosymbiosis
Eukaryotes Inherited Bacterial Lipids
Eukaryotes Have Huge Advantages Over Prokaryotes
Mitochondria Are Advantageous for Energetics
Large Size Is Advantageous for Eukaryotes
The Fate of Life on Earth
Earth Will Be Habitable for Another 1.5 Billion Years
Mariner Missions Reveal a Cold Arid World
Mars Is a Planetary Embryo
Mars Has Two Very Different Hemispheres
Spectrometry Reveals the Nature of Planetary Surfaces
The Martian Crust Is Mostly Basalt
Water Ice Is Abundant on Mars
Mars Has Substantial Frozen Water
Water Has Flowed on Mars
Mars Has Numerous Fluvial Features
Mars Exploration Rovers Have Searched for Signs of Liquid Water
Global Geological Markers Can Reveal How Long Mars Was Wet
Mars Has Experienced Three Climates
Liquid Water Cannot Exist at the Martian Surface Today
Detection of Methane in the Martian Atmosphere Is Dubious
Atmosphere of Early Mars
Was Mars Episodically Warm and Wet?
Mars and Life
The Viking Experiments Were Designed to Detect Life
Does ALH84001 Harbor Evidence of Life?
Martian Life Could Be Based on Iron and Sulfur Metabolism
Life Might Exist Beyond the Conventional Habitable Zone
Titan Has a Dense Atmosphere
Atmospheric Methane Must Be Continually Regenerated
Organic Chemistry Occurs in Titan’s Atmosphere
Could There Be Life on Titan?
Enceladus Has Been Resurfaced Multiple Times
Enceladus Cryovolcanic Plumes Contain Water Vapor
What Heats Enceladus Now?
Europa Is a Differentiated World
There Is Good Evidence for a Europan Ocean
How Thick Is the Europan Crust?
The Europan Surface Is Chemically Altered
What Is the Astrobiological Potential of Europa?
The First Exoplanets Were Found by Timing Pulsars
The First Exoplanet Around a Main Sequence Star Was Discovered in 1995
Some Exoplanets Can Be Imaged Directly
Planets Are Extremely Dim Compared to Their Host Stars
Coronagraphs Create Artificial Eclipses
Nulling Interferometry Cuts Out Starlight
Direct Imaging Reveals High Mass Planets
Astrometry Detects Binary Systems by Stellar "Wobble"
The Radial Velocity Method Uses the Doppler Effect
Defining the Radial Velocity
Finding the Period and Semi-Major Axis of an Exoplanet’s Orbit
The RV Method Provides a Lower Bound on Planetary Mass
The RV Method Is Biased to Detect Massive Planets with Short Periods
Exoplanets Are Revealed When They Transit Their Star
Exoplanet Transits Dim Starlight
The Transit Method Allows Several Parameters to Be Deduced
Transit Timing Variation Uncovers Multiple and Circumbinary Exoplanets
Transits Can Potentially Detect Earth-Mass Planets
Most Transit Detections Have Been Made from Space
Gravitational Lensing Can Unveil Exoplanets
Gravitational Microlensing Events Are Short-Lived
Microlensing Yields Information About Exoplanet Systems
There Are Both Pros and Cons to Lensing
Detection Methods Are Biased
Survey Statistics Can Estimate What We Cannot Detect
Surveys Probe Exoplanet Properties
Exoplanet Diversity Is Large
Exoplanets Are Classified According to Their Size
Hot Jupiters Were Discovered Early
Small Exoplanets Are Commonest
Exoplanet Composition Can Sometimes Be Deduced
Exoplanet Temperature Can Be Estimated
Exoplanet Host Star Properties
Metal-Rich Stars Are More Likely to Host Gas Giants
Did Terrestrial Planets Form 11 Billion Years Ago?
Most Stars with Planets Have Low Lithium Abundance
η⊕ Is the Proportion of Stars with Habitable Planets
An Earth-Sized Planet in the Habitable Zone Has Been Discovered
How to Define a Habitable Zone
η⊕ Has Been Derived from Kepler Data
Habitable Planets Around M-Dwarfs?
Habitability of Planets and Eccentricity Orbits
Planets Exist in Binary Systems
The Galactic and Habitability
The Milky Way Is a Spiral Galaxy
Galactic Chemistry Influences Habitability
The Galaxy Has a Habitable Zone
Are There Habitable Planets in Clusters?
Prospecting for Life
Rare Earth versus the Principle of Mediocrity
Is an Early Origin a Guide to the Probability of Life?
Life May Be Rare or Common in the Galaxy
Several Hard Steps Could Be Needed for Intelligent Observers to Emerge
What Are the Hard Steps?
Is Life Seeded from Space?
Survival of Ancient Bacteria Makes Panspermia Plausible
Life May Be Uncommon Despite Panspermia
Radiation Is a Major Hazard
Can Micro-Organisms Survive Lithopanspermia?
Metrics for Extraterrestrials
Is the Drake Equation More than a Guess?
Alternatives to the Drake Equation Have Been Developed
SETI and the Fermi Paradox
How Far Away Would Passive Radiation Reveal Our Presence?
Where Is Everybody?
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.