Robert M. Hazen
Joseph Henry Press
Washington, DC
Joseph Henry Press • 500 Fifth Street, NW • Washington, DC 20001
The Joseph Henry Press, an imprint of the National Academies Press,
was created with the goal of making books on science, technology, and
health more widely available to professionals and the public. Joseph
Henry was one of the founders of the National Academy of Sciences
and a leader in early American science.
Any opinions, findings, conclusions, or recommendations expressed
in this volume are those of the author and do not necessarily reflect the
views of the National Academy of Sciences or its affiliated institutions.
Library of Congress Cataloging-in-Publication Data
Hazen, Robert M., 1948-
Genesis : the scientific quest for life’s origin / by Robert M. Hazen.
p. cm.
Includes bibliographical references and index.
ISBN 0-309-09432-1
1. Life—Origin. I. Title.
QH325.H39 2005
576.8′3—dc22
2005012839
ISBN-13: 978-0-309-10310-7
(paperback)
ISBN-10: 0-309-10310-X
(paperback)
Cover design by Michele de la Menardiere.
Cover photo of microscopic vesicles courtesy of Robert M. Hazen and
David W. Deamer. A key step in life’s origin may have been the sponta-
neous assembly of these cell-like spheres of molecules.
Illustrations on pages 18, 145, 153, 159, 195, and 226-227 by Matthew
Frey, Wood Ronsaville Harlin, Inc., Annapolis, Maryland. Copyright
Wood Ronsaville Harlin, Inc.
Copyright 2005 by Robert M. Hazen. All rights reserved.
Printed in the United States of America.
For Glenn, Steve, and Hat
Contents
Foreword
ix
by David Deamer
Preface
xiii
Prologue
1
PART I
EMERGENCE AND THE ORIGIN OF LIFE
1
The Missing Law
11
2
What Is Life?
25
3
Looking for Life
33
4
Earth’s Smallest Fossils
47
5
Idiosyncrasies
61
Interlude—God in the Gaps
77
PART II
THE EMERGENCE OF BIOMOLECULES
6
Stanley Miller’s Spark of Genius
83
7
Heaven or Hell?
95
8
Und er Pressure
107
9
Productive Environments
121
vii
viii
CONTENTS
129
PART III
THE EMERGENCE OF MACROMOLECULES
10 The Macromolecules of Life
133
11 Isolation
143
12 Minerals to the Rescue
155
13 Left and Right
167
Interlude—Where Are the Women?
187
PART IV
THE EMERGENCE OF SELF-REPLICATING SYSTEMS
14 Wheels Within Wheels
191
15 The Iron–Sulfur World
205
16 The RNA World
215
17 The Pre-RNA World
221
18 The Emergence of Competition
233
19 Three Scenarios for the Origin of Life
241
Epilogue—The Journey Ahead
245
Notes
247
Bibliography
293
Index
323
Foreword
A central theme of this book is the concept of emergence. What do we
mean when we say that something emerges? In common usage, a shad-
owy figure emerges from the dark, a submarine emerges from the sea, a
plot emerges in a novel. But emergence has come to have a different
meaning in scientific terminology. Researchers are increasingly begin-
ning to use emergence to describe processes by which more complex
systems arise from simpler systems, often in unpredictable fashion.
This use of the word “emergence” is in a sense the opposite of re-
ductionism, the view that any phenomenon can be explained by un-
derstanding the parts of that system. Because reductionism has been
such a powerful tool in the sciences, some scientists shy away from the
concept of emergence, thinking it to be slightly weird. But there can be
little doubt that the word itself is useful in referring to some of the
most remarkable phenomena we observe in both nature and in the
laboratory.
An example is the way that orderly arrangements of molecules can
appear spontaneously. For instance, if we add soap molecules to water,
at first there is nothing present but the expected clear solution of indi-
vidual molecules dissolved in the water. But at a certain concentration,
additional molecules no longer dissolve but instead begin to associate
into small aggregates called vesicles. And as the concentration increases,
the vesicles begin to grow into membranous layers of soap molecules
that cloud the originally clear solution. Finally, if we blow air through a
ix
x
FOREWORD
straw into the solution, much larger structures—soap bubbles—ap-
pear at the surface.
Such emergent phenomena—phenomena that exhibit self-orga-
nization—are common in our everyday experience. The laws of chem-
istry and physics permit certain kinds of molecules to self-assemble
into aggregates that have surprising structures and properties. Some-
times the process is spontaneous, as in the formation of vesicles, but in
other instances an input of energy is required to drive self-assembly. If
we did not know by observation that soap molecules can self-assemble,
we could not have predicted that vesicles would suddenly appear if we
simply increased the concentration of soap molecules in solution. And
even though we know that vesicles form, there is still no equation that
can predict exactly what concentration of soap is required to form
them.
Life on Earth arose through a sequence of many such emergent
phenomena, which define the subject of this book. Imagine that we
could somehow travel back in time to the prebiotic Earth, some 4 bil-
lion years ago. It is very hot—hotter than the hottest desert today. As-
teroid-sized objects bombard the surface. Comets crash through the
atmosphere—no oxygen yet, just a mixture of carbon dioxide and ni-
trogen—and add more water to a globe-spanning ocean. Landmasses
are present, but they are volcanic islands resembling Hawaii or Iceland,
rather than continents.
Imagine that we are standin
g on one such island, on a beach com-
posed of black lava rocks, with tide pools containing clear seawater. We
can scrutinize that water with a microscope, but there is nothing living
to be seen in it, only a dilute solution of organic compounds and salts.
If we could examine the mineral surfaces of the lava rocks, we would
see that some of the organic compounds have formed a film adhering
to the surface, while others have assembled into aggregates that dis-
perse into the seawater.
Now imagine that we return 100 million years later. Not much has
changed. The landmasses are still volcanic islands, meteorite impacts
have dwindled, and it might be a little less hot. But, when we look at
the tide pools, we see a cloudiness that was not apparent earlier, and
the mineral surfaces are coated with a thin film of slime. When we
examine the water and lava with our microscope, we discover immense
numbers of bacteria swarming in multiple layers. Life has begun.
What happened in 100 million years that led to the origin of life?
FOREWORD
xi
This is a fundamental question of biology, and the answer will surely
change the way we think about ourselves as well as our place in the
universe, because if life could begin on Earth, it could begin by similar
processes on Earth-like planets circling other stars throughout the uni-
verse. The origin of life is the most extraordinary example of an emer-
gent phenomenon, and the process by which life began must involve
the same kinds of intermolecular forces and self-assembly processes
that cause soap to form membranous vesicles. The origin of life must
also have in some way incorporated the reactions and products that
occur when energy flows through a molecular system and drives it to-
ward ever more complex systems with emergent properties.
This book explores the concept of emergence and the origin of life
in a way that has never before been attempted. Science has thousands
of investigators who pry away at highly focused aspects of the great
questions, hardly aware of the vast unexplored problems spreading
around them to the horizon. But each science has a few explorers—
rare personalities willing to step back from the microscopic details,
look toward the horizon, and gamble that patterns will emerge from
their broader perspective. Robert Hazen is such an explorer, and this
book is a journal of his explorations.
Genesis: The Scientific Quest for Life’s Origin is a pretty amazing
book. Many authors of popular science books are teachers and profes-
sors, and it is only natural that their books come across that way: as
lectures—factual, conceptual, theoretical. Occasionally, an author is
able to assemble facts, concepts, and theory in a creative way to pro-
duce a book that introduces a significant new paradigm. Darwin did
that, and more recently E. O. Wilson and Stephen Jay Gould.
Hazen has taken a different approach, and a different set of words
describes this book: It is personal, even intimate, filled with passion for
the scientific enterprise. You will find facts, concepts, and theories here,
too—but beyond that you will discover glimpses of scientists in action,
chasing ideas in the lab and the field. You will find people struggling
with experimental results, with interpretations, and with each other.
You will find drama, which exists in the sciences as much as in any
other human endeavor. And you will find cliffhangers: Will a future
experiment show that Nick Platts’ idea about primitive genetic poly-
mers is correct? Or will it dash his hopes? Will new evidence permit a
choice between the conflicting claims of Bill Schopf and Martin Brasier
about the Apex Chert fossils?
xii
FOREWORD
Like Wilson and Gould, Hazen is a working scientist—a mineralo-
gist who has broadened his field of research in order to tackle, with his
colleagues at the Carnegie Institution’s Geophysical Laboratory, some
of the deepest problems of biology. Where did organic compounds
come from to kick-start the life process on the early Earth? How did
life become chiral (that is, “handed”), starting with mixtures of mol-
ecules that differ only in whether their structures rotate polarized light
to the left or to the right? How did metabolic pathways arise from the
interaction of organic molecules and mineral surfaces? A convincing
answer to any one of these questions would be a capstone to a remark-
able life in science. In this book you will learn how Hazen and other
explorers are struggling to find those answers.
David Deamer
Santa Cruz, California
May 2005
Preface
And God said, “Let the waters bring forth swarms of living
creatures.”
Genesis 1:20
How did life arise? Why are we here? For thousands of years humans
have longed for answers to these deeply resonant questions.
The Biblical account in the first chapter of Genesis, though rich in
poetic metaphor, hardly puts the origin question to rest. Barring di-
vine intervention, life must have emerged by a natural process—one
fully consistent with the laws of chemistry and physics. Scientists be-
lieve in a universe ordered by natural laws; they resort to the power of
observations, experiments, and theoretical reasoning to discover those
laws. The methods of science are unsuited to address the “why” of our
existence, but many of us feel driven to understand the nitty-gritty
chemical details of how life began.
Scientists surmise that life arose on the blasted, primitive Earth
from the most basic of raw materials: air, water, and rock. Life emerged
nearly 4 billion years ago by natural processes completely in accord
with the laws of chemistry and physics, yet details of that transforming
origin event pose mysteries as deep as any facing science. How did non-
living chemicals become alive?
It is possible, of course, that life arose through an improbable se-
quence of many chemical reactions. If so, then living worlds will be
rare in the universe and laboratory attempts to understand the origin
process will be doomed to frustration. An unlikely sequence of
unknown steps cannot be reproduced in any plausible experimental
program.
xiii
xiv
PREFACE
Alternatively, the universe may be organized in such a way that life
emerges as an inevitable consequence of chemistry, given an appropri-
ate environment and sufficient time. Starting with water, organic mol-
ecules, and a suitably protected energy-rich environment, life may be
very likely to emerge from nonlife on any hospitable planet or moon.
This scenario allows for fruitful systematic scientific study. If life is
likely to arise whenever and wherever appropriate conditions occur,
then scientists can hope to study life’s origins in the lab through ex-
periments that simulate those conducive conditions. Not surprisingly,
most origin-of-life investigators favor the view that life is a cosmic im-
perative and that it is only a matter of time before we figure out how it
happened. In this scenario, genesis occurs throughout the universe all
the time.
Genesis: The Scientific Quest for Life’s Origin attempts to portray this
great adventure—the effort to deduce how life began on the ancient
Earth. The epic history of life’s chemical origins is woefully incom-
plete. Daunting gaps exist in our knowledge, and much of what we
have learned is hotly debated and subject to conflicting interpreta-
tions. Consequently, this book is as much about the process of defin-
ing what we do not know as it is about recounting well-established
data and concepts. One objective of the book is to describe our present,
imperfect state of understanding—and to offer a conceptually simple
scenario for life’s chemical origins. This theory synthesizes two funda-
mental frontier efforts: the mind-expanding theoretical field of emer-
gence and the astonishing experimental discoveries in prebiotic
chemistry.
The science of emergence seeks to understand complex systems—
systems that display novel collective behaviors that arise from the
interactions of many simple components. From gravitational interac-
tions of individual stars emerge the glorious sweeping arms of spiral
galaxies. From the chemical interactions of individual ants emerge the
extraordinarily complex social behavior of ant colonies. From the elec-
trical interactions of individual neurons in your brain emerge thought
and self-awareness. Emergence is nature’s most powerful tool for mak-
ing the universe a complex, patterned, entertaining place to live.
PREFACE
xv
Life itself is arguably the most remarkable of all emergent systems.
Many origin-of-life experts adopt the view that life began as an inexo-
rable sequence of emergent events, each of which was an inevitable
consequence of interactions among versatile carbon-based molecules.
Each emergent episode added layers of chemical and structural com-
plexity to the existing environment. Intensive experiments at laborato-
ries around the world reveal, step-by-step, the essential life-triggering
reactions that must occur throughout the cosmos. First came the
carbon-containing biomolecules, synthesized in unfathomable abun-
dance on comets and asteroids, in the black near-vacuum of space, on
the surface of the young Earth, and deep within our planet’s restless
crust. Then came the emergence of larger molecular structures—the