Alone in the Universe: Why Our Planet Is Unique

208 Pages·2011·1.05 MB·English

by  John Gribbin

Contents
Acknowledgements
Preface: The Only Intelligent Planet
Introduction: One in a Trillion
Across the Milky Way
Hot jupiters
Planets in profusion
Dusty beginnings
Cosmic chemistry
The life of Gaia
Searching for other Gaias
Chapter 1: Two Paradoxes and an Equation
The Cosmic Lottery and the Drake Equation
The Inspection Paradox and the Copernican Principle
Panspermia and the Fermi Paradox
Probing for an Answer
Chapter 2: What’s So Special about Our Place in the
Milky Way?
Making Galaxies
Making Metals
Mixing Metals in the Milky Way
Our Place in the Milky Way
The Galactic Habitable Zone
Catastrophic Comets
Chapter 3: What’s So Special about the Sun?
The Narrow Zone of Life
The Sun is not an Average Star
Perturbing Partners
Blasts from the Past
The Mystery of Solar Metallicity
Until the Sun Dies
Postponing Doomsday
Chapter 4: What’s So Special about the Solar System?
Too Hot to Handle
The Geography of the Solar System
Making Planets
Making the Solar System
Making the Earth
The Special One
Chapter 5: What’s So Special about the Earth?
Like a Diamond in the Sky
A Planetary Jigsaw Puzzle
Creating Continents
A Field of Force
Venus and Mars
A Planetary Stabilizer
Plate Tectonics and Life
Chapter 6: What’s So Special about the Cambrian
Explosion?: I. Contingency and Convergence
The Cambrian Explosion
The Burgess Shale
Contingency
Convergence
The Third Way
Chapter 7: What’s So Special about the Cambrian
Explosion?: II. Hothouse Venus/Snowball Earth
After the Deep Freeze
Tipping the Balance
From without or within?
The Archetypal Impact
Cosmic Clouds and Comet Dust
Diamond Dust and a Facelift for a Goddess
Chapter 8: What’s So Special about Us?
Chance, Necessity and the Decimal System
The Molecular Clock
The Trigger for Change
The Pacemaker of Human Evolution
The Fate of Technological Civilization
The Fate of the Earth
No Second Chance
Further Reading
Index

Copyright © 2011 by John and Mary Gribbin. All rights reserved Published by
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It seems almost as if our Galaxy were a giant warehouse containing the spare
parts needed for life.
James Lovelock, FRS
For Simon Goodwin, who was generous enough not to write it first!
Acknowledgements
Thanks to Simon Goodwin, Douglas Lin, Charley Lineweaver, Jim Lovelock,
Mac Low, Josep Trigo-Rodriguez and the Sussex University astronomers for
discussions and advice on various aspects of this story. Sharing an office with
Bernard Pagel in recent years gave me an opportunity to learn more than I
realized at the time about the chemical composition of the stars and how it
changes as time passes. As ever, Mary Gribbin played a key role in ensuring that
my words are intelligible, and the Alfred C. Munger Foundation provided a
contribution to our travel and other expenses.
Preface
The Only Intelligent Planet
Do we owe our existence to the impact of a ‘supercomet’ with Venus 600 million
years ago? A decade ago the idea might have seemed laughable. But now we
know that there are icy objects the size of Pluto in orbits far out on the fringe of
the Solar System, we know that Earth’s Moon was formed by the impact of an
object the size of Mars with Earth, we know from chaos theory that no orbit
around the Sun is stable, and, crucially, we know that something catastrophic
happened to both Venus and Earth at the same time, just before the explosion of
life on Earth that led to our existence. Coincidence? Maybe. But if so, it is the
most significant in a chain of coincidences that led to the emergence of
intelligent life on Earth. And that chain has so many weak links that it may mean
that, for all the proliferation of stars and planets in the Universe, as an intelligent
species we may be unique.
There are several hundred billion stars in our Milky Way Galaxy. At a
conservative estimate, several billion of them are orbited by planets capable of
supporting life. There may be more habitable planets in the Galaxy than there are
people on planet Earth. But ‘habitable’ does not mean ‘inhabited’. The thesis of
this book is that intelligent civilization exists only on Earth. The reason is
connected with the series of cosmic events that affected both Venus and Earth
some 600 million years ago. But this is only part of the story, just one of the
astronomical and geophysical reasons why the Earth is special, and probably
unique.
Since the time of Copernicus, the progress of science has resulted in a steady
displacement of the perceived place of human beings from centre stage in the
Universe. By the end of the twentieth century, the received wisdom was that we
are an ordinary kind of animal living on an ordinary planet orbiting an ordinary
star in the backwoods of an unspectacular galaxy. But this image of the Earth
and humankind as an insignificant unit in the Universe may be wrong. This book
challenges that idea and suggests that human beings are special after all – the
unique products of an extraordinary set of circumstances that have as yet
occurred nowhere else in the Galaxy, and possibly not in the entire Universe. An