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LIFE EVERYWHERE

The Maverick Science of Astrobiology


David Darling





PREFACE




Something extraordinary has happened over the past decade. Without any fanfare, scientists the world over have reached a consensus on one of the most profound questions ever to challenge the human mind: Are we alone? In all of this vast and ancient cosmos, is life confined to the Earth?

No. Almost beyond doubt, life exists elsewhere. Probably, in microbial form at least, it is widespread. And more likely than not, we will find incontestable evidence of it quite soon — perhaps within the next ten to twenty years. These are the core elements of the remarkable new accord that is now routinely accepted by researchers across a spectrum of disciplines.

Behind this surge in scientific optimism about the prospects for alien life lies a rush of remarkable discoveries. A bewildering assortment of (mostly microscopic) life-forms has been found thriving in what were once thought to be uninhabitable regions of our planet. These hardy creatures have turned up in deep, hot underground rocks, around scalding volcanic vents at the bottom of the ocean, in the desiccated, super-cold Dry Valleys of Antarctica, in places of high acid, alkaline and salt content, and below many meters of polar ice. The range of locales where organisms could be expected to survive in the universe is thus vastly expanded. Some deep-dwelling, heat-loving microbes, genetic studies suggest, are among the oldest species known, hinting that not only can life thrive indefinitely in what appear to us totally alien environments, it may actually originate in such places. If so — if the cradles of biogenesis tend to be hot, dark, sub-surface hells rather than our familiar sun-drenched surface edens — then the widespread appearance of life throughout the cosmos is made much more likely.

Scientific opinion has also shifted dramatically toward the view that life may be "easy" — able to assemble itself from simpler components at the slightest opportunity. How else to account for the signs in ancient rocks that bacteria proliferated on Earth as long ago as 3.8 billion years, during the intense bombardment phase following the birth of our solar system? Terrestrial life appeared almost before it had a reasonable chance of long-term survival, then somehow managed to weather the ferocious early storm of asteroid and comet impacts. An increasingly common claim among researchers is that life may arise inevitably whenever a suitable energy source, a concentrated supply of organic (carbon-based) material, and water occur together.

These ingredients are starting to look ubiquitous in space. Comets, in particular, are increasingly seen as significant vehicles for delivering water and organic cocktails to infant worlds. And with the discovery on Earth of meteorites from Mars, the interplanetary transfer of biochemicals or even life itself has become a respectable topic of debate.

Both within and beyond the solar system, the list of potential places where life may have become established is growing fast. Close to home, Jupiter’s moons Europa and Ganymede have taken on biological interest with the realization that they may harbor a chemical-rich oceans of water beneath their icy surfaces. Further afield, the finding of dozens of extrasolar planets — almost as soon as we knew how to look for them — encourages scientists to think that planetary systems around stars are the rule rather than the exception. From origin of life studies to complexity theory, from extrasolar planet detection to work on extremophiles, from pre-Cambrian paleontology to interstellar chemistry, the emerging message is clear and virtually unanimous: extraterrestrial life is there for the finding.

Having generally agreed that it’s only a matter of time before the first alien organisms come to light, scientists are now busily laying the foundations of the new field of astrobiology. (The study of life in the universe has been variously called exobiology (first by geneticist Joshua Lederberg in 1960), bioastronomy (a more recent name), and astrobiology (oldest of all, mentioned in Soviet literature as far back as 1953). These terms are still used more or less interchangeably, but "astrobiology" is in the ascendancy thanks to its recent adoption by NASA.) They are asking: What are the general conditions needed for life to appear? How common it will prove to be? Where it will be found? What it will be like? These are now respectable and intensely debated mainstream issues — the subject of major conferences and numerous scientific papers every month, a focal point of interdepartmental projects at a growing number of universities and other research organizations, and a key motivating influence behind international space programs. They are the raison d’être of NASA’s Astrobiology Institute, which began operations in 1998 and saw the Nobel Prize winner Baruch Blumberg (renowned for his work on hepatitis B) appointed as its first head in 1999. They motivate the University of Washington’s astrobiology program in Seattle, which welcomed its first intake of graduate students in 1999. They formed the topic of the first annual conference devoted to the science of astrobiology, held at NASA Ames in April 2000. "We are witnessing not just a shift in scientific paradigm but, more important, a shift in cultural acceptability among scientists," said extrasolar planet hunter Geoff Marcy. Poised on the brink of a momentous breakthrough that will change forever how humankind thinks about itself and the universe around it, astrobiology is fast coming of age.

Like all branches of science reaching toward maturity, astrobiology is alive with diverse theories, experimental data, rumors and conjecture. These are extraordinarily frenetic times, an immensely fertile period of thought. The corridors outside conference halls are crowded with researchers in animated conversation, vying to get across their points of view, forming camps of opinion, pushing back the frontiers of knowledge and surmise about what lies out there.

At first glance, it may seem that apart from their broad agreement that terrestrial life is not unique, those engaged in this new endeavor are more in discord than harmony. Certainly there are many differences of opinion about specific issues, from claims about Martian “fossils” to the steps involved in life’s genesis. That’s to be expected. But it isn’t too early to make out, amid the tumult of claims and counter-claims, the beginnings of a general theory of biology, a framework of concepts that underpins the development of life wherever it takes place.

This book is a report from the frontline of astrobiological research, an examination of the issues, arguments and experimental results foremost in the minds of those who are spearheading this astonishing new field. Beyond that, it is an attempt to see the way ahead, to identify the concepts that may eventually unify our understanding of life in a broader context. On what may be the brink of our first encounter with an alien species, we ask: What principles govern the emergence and evolution of life throughout the cosmos? Where can we expect to find other living worlds, and what will we discover upon them?


contents | chapter 1: The Intimate Mystery