The Fifth Miracle: The Search for the Origin and Meaning of Life - Hardcover

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Paul Davies is a theoretical physicist and the bestselling author of more than twenty books. He is the recipient of the 1995 Templeton Prize for his work on the philosophical meaning of science. His books include About Time, The Mind of God, God and the New Physics, The Cosmic Blueprint, and Other Worlds.

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CHAPTER 1: The Meaning of Life

Imagine boarding a time machine and being transported back four billion years. What will await you when you step out? No green hills or sandy shores. No white cliffs or dense forests. The young planet bears little resemblance to its equable appearance today. Indeed, the name "Earth" seems a serious misnomer. "Ocean" would suit better, for the whole world is almost completely submerged beneath a deep layer of hot water. No continents divide the scalding seas. Here and there the peak of a mighty volcano thrusts above the surface of the water and belches forth immense clouds of noxious gas. The atmosphere is crushingly dense and completely unbreathable. The sky, when free of cloud, is lit by a sun as deadly as a nuclear reactor, drenching the planet in ultraviolet rays. At night, bright meteors flash across the heavens. Occasionally a large meteorite penetrates the atmosphere and plunges into the ocean, raising gigantic tsunamis, kilometers high, which crash around the globe.

The seabed at the base of the global ocean is unlike the familiar rock of today. A Hadean furnace lies just beneath, still aglow with primeval heat. In places the thin crust ruptures, producing vast fissures from which molten lava erupts to invade the ocean depths. The seawater, prevented from boiling by the enormous pressure of the overlying layers, infuses the labyrinthine fumaroles, creating a tumultuous chemical imbroglio that reaches deep into the heaving crust. And somewhere in those torrid depths, in the dark recesses of the seabed, something extraordinary is happening, something that is destined to reshape the planet and, eventually perhaps, the universe. Life is being born.

The foregoing description is undeniably a speculative reconstruction. It is but one of many possible scenarios offered by scientists for the origin of life, but increasingly it seems the most plausible. Twenty years ago, it would have been heresy to suggest that life on Earth began in the torrid volcanic depths, far from air and sunlight. Yet the evidence is mounting that our oldest ancestors did not crawl out of the slime so much as ascend from the sulfurous underworld. It may even be that we surface dwellers are something of an aberration, an eccentric adaptation that arose only because of the rather special circumstances of Earth. If there is life elsewhere in the universe, it may well be almost entirely subterranean, and only rarely manifested on a planetary surface.

Although there is now a measure of agreement that Earth's earliest bioforms were deep-living microbes, opinion remains divided over whether life actually began way down in the Earth's crust, or merely took up residence there early on. For, in spite of spectacular progress over the past few decades in molecular biology and biochemistry, scientists still don't know for sure how life began. The outline of a theory is available, but we are a long way from having a blow-by-blow account of the processes that transformed matter into life. Even the exact location of the incubator remains a frustrating mystery. It could be that life didn't originate on Earth at all; it may have come here from space.

The challenge facing scientists struggling to explain the origin of life is the need to piece together a narrative of events that happened billions of years ago and have left little or no trace. The task is a daunting one. Fortunately, during the last few years some remarkable discoveries have been made about the likely nature of Earth's most primitive organisms. There have also been great strides in laboratory procedures, and a growing understanding of conditions in the early solar system. The recent revival of interest in the possibility of life on Mars has also served to broaden the thinking about the conditions necessary for life. Together, these developments have elevated the subject from a speculative backwater of science to a mainstream research project.

The problem of how and where life began is one of the great outstanding mysteries of science. But it is more than that. The story of life's origin has ramifications for philosophy and even religion. Answers to such profound questions as whether we are the only sentient beings in the universe, whether life is the product of random accident or deeply rooted law, and whether there may be some sort of ultimate meaning to our existence, hinge on what science can reveal about the formation of life.

In a subject supercharged with such significance, lack of agreement is unsurprising. Some scientists regard life as a bizarre chemical freak, unique in the universe, whereas others insist that it is the expected product of felicitous natural laws. If the magnificent edifice of life is the consequence of a random and purely incidental quirk of fate, as the French biologist Jacques Monod claimed, we must surely find common cause with his bleak atheism, so eloquently expressed in these words: "The ancient covenant is in pieces: man at last knows that he is alone in the unfeeling immensity of the universe, out of which he has emerged only by chance. Neither his destiny nor his duty have been written down." But if it transpires that life emerged more or less on cue as part of the deep lawfulness of the cosmos -- if it is scripted into the great cosmic drama in a basic manner -- it hints at a universe with a purpose. In short, the origin of life is the key to the meaning of life.

In the coming chapters I shall carefully examine the latest scientific evidence in an attempt to confront these contentious philosophical issues. Just how bio-friendly is the universe? Is life unique to Planet Earth? How can something as complex as even the simplest organism be the product of straightforward physical processes?

Life's mysterious origin

The origin of life appears...to be almost a miracle, so many are the conditions which would have had to be satisfied to get it going.

FRANCIS CRICK

According to the Australian Aborigines of the Kimberley, in the Creation Time of Lalai, Wallanganda, the sovereign of the galaxy and maker of the Earth, let fresh water fall from space upon Wunggud, the giant Earth Snake. Wunggud, whose very body is made of the primeval material, was coiled into a ball of jellylike substance, ngallalla yawun. On receiving the invigorating water, Wunggud stirred. She formed depressions in the ground, garagi, to collect the water. Then she made the rain, and initiated the rhythmic processes of life: the seasons, the reproductive cycles, menstruation. Her creative powers shaped the landscape and brought forth all creatures and growing things, over which she still holds dominion.

All cultures have their creation myths, some more colorful than others. For centuries, Western civilization looked to the Bible for enlightenment on the subject. The biblical text seems disappointingly bland when set beside the Australian story: God created life in more or less its present form ab initio, as the fifth miracle.

Not far from the Kimberley -- across the Great Sandy Desert, in the mountains of the Pilbara -- lie the oldest known fossils on Earth. These extraordinary remains form part of the scientific account of creation. Science takes as its starting point the assumption that life wasn't made by a god or a supernatural being: it happened unaided and spontaneously, as a natural process.

Over the past two centuries, scientists have painstakingly pieced together the history of life. The fossil record shows clearly that ancient life was very different from extant life. Generally speaking, the farther back in time you go, the simpler were the living things that inhabited Earth. The great proliferation of complex life forms occurred only within the last billion years. The oldest well-documented true animal fossils, also to be found...