"Life as we know it is assertive, demanding, and unstoppable." So reads a passage in the introduction of an intriguing work about some of the greatest and most difficult questions that still confront science: How did life originate on Earth? What did the earliest primitive organisms look like? Were they based on RNA, DNA, or on something we would hardly recognize today? Is there life elsewhere in the universe?
In "The Spark of Life" (Perseus Publishing), Christopher Wills, a professor of biology at the University of California, San Diego (UCSD), and Jeffrey Bada, a professor of marine chemistry at Scripps Institution of Oceanography at UCSD, have crafted a down-to-earth story about the quest for the origin of life-in all its fascinating detail.
Untangling a century of debate, Wills and Bada explore and debunk theories about the origins of life, and in the process wander from one end of the world to the other and "venture into the depths of the earth and into the Stygian blackness of the deep ocean." At the end of the book, the authors push the examination into space, "traveling through near and far reaches of the universe as we search for clues to life elsewhere."
In addition to examining theory, Wills and Bada also present their own calculated scenario for life's beginnings. Life did not originate in Earth's subterranean depths, as some have contended, but rather on Earth's surface, where a primitive form of natural selection spawned the first genetic material.
The authors tell of erupting geysers, intense wave action, lightning flashes, and blazes of sunlight that worked in combination with an atmosphere of methane,
ammonia, hydrogen, and water vapor, to produce a primeval soup of the basic ingredients for the beginnings of life. They give a magnificent description of what the early Earth looked like, with constant asteroid bombardment, killer tides, a lethal atmosphere, and a strange carpet of slime. They also discuss where in our solar system, and beyond, similar processes may have resulted in the origin of extraterrestrial life.
"What we try to do in the book is present your mind with a picture of what this first living entity was on Earth-it's nothing like you and I are familiar with-it's beyond our experience," said Bada. "It's something very primitive. You can't see it, but it is living, so you have to conjure up what it is."
"The fact that the Earth was such an awful place back then is not something that is fully appreciated by people working in this field," said Wills. "But that was the challenge-the fact that some groups of molecules could cling to rocks and not be washed away, which would be the very primitive beginning of something that could lead to something more complex. It's that sort of reasoning that we follow throughout the book. Even at present there is an incredible diversity of life that can survive in all kinds of environments. Life is resourceful."
Wills said the highly subdivided and cyclical nature of the environments at the surface-the tides, waves and storms-are what provided the driving force for the evolution and diversification of life. That's something that wouldn't be possible in the deep recesses of the Earth.
"I think Chris Wills and I really complemented each other extremely well," said Bada. "I brought in the chemistry, geology, and astronomy parts, and Chris brought in all of the biology, evolution, and tree-of-life material."
"The Spark of Life" also tackles the circular problem associated with how the first living material was able to replicate itself. Did genes come first or did life start with the cellular chemical pathways that function as metabolism?
In other words, as the book puts it, you need an engine (metabolic processes) in order to drive a car, but you also need a blueprint and a factory (genetic information) in order to make more engines.
According to Wills, life did not originate from a single self-replicating molecule, as some chemists believe. It was much more complex, requiring the cooperation of complexes of enzymes and other molecules. "There were all sorts of things that had to go on simultaneously," he said. "The only way you're going to get that is if the world was a very complicated place, right from the beginning."
Wills added that the only way for chemists to understand the origin of life is to re-examine the famous Miller-Urey experiment and start putting more complexity into the system. "Then we can ask, How complicated are the molecules we get out? Do we see any signs of replicative behavior among these molecules? Until we do that experiment, I don't think anyone will get a handle on it."
"Arguments about the origin of life tend to have this strange recursive quality, circling maddeningly around the problem without ever quite coming to grips with it," the book explains. "We are going to try to break this circle."
Christopher Wills is a UCSD professor of biology whose books include "Yellow Fever, Black Goddess," and "Children of Prometheus." Jeffrey Bada is a professor of marine chemistry and director of the NASA Specialized Center of Research and Training in Exobiology at Scripps Institution of Oceanography, UCSD.
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