H00102--00A, Front mat Genesis Read online

  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

  Interlude—Mythos Versus Logos

  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