In this news-conscious age, everyone knows the journalist’s litany of prime questions: who, what, when, where, why, how. About the origin of life, scientists’ questions are similar, but more restricted. Setting aside thewho(no humans were on hand to observe the event), thewhere(unanswerable except in the broadest terms—on Earth, in water, probably in oceans), and thewhy(a question posed by philosophers and theologians, not scientists), we are left with the three great puzzles this volume addresses:Whatis the origin of life,whendid it begin, andhow?

At first blush, thewhatseems easy...

There are three major singularities in the world—the observable universe, life on Earth, and human beings. For the most part, we agree on concepts of what the cosmos and human beings are, but we have reached no consensus on what life is. It is easier to recognize life, in all its common forms, than it is to define it. In 1976, during NASA’s Viking Project to Mars, the late Carl Sagan and I were at the Jet Propulsion Laboratory in Pasadena, California, discussing this very problem. Asked if we would actually recognize life on Mars were we lucky enough...

According to modern theory, life arose on the primitive Earth by a process of prebiotic chemical evolution. This process began with syntheses of organic chemical precursors of proteins, nucleic acids, and membranes in the early atmosphere and ocean, and ended with the emergence of life forms capable of self-replication—forms that could undergo Darwinian evolution through mutation and natural selection. Although most researchers accept this view of prebiotic evolution, opinions diverge on the nature and sequence of chemical events between the first and last stages. Many theoretical paths meander through this murky middle ground, but the track culminating in biological...

Along with his books, notes, letters, and papers, Charles Robert Darwin bequeathed two recipes to succeeding generations. The first, written in his wife’s recipe book, describes the way to boil rice:

Add salt to the water and when boiling hot, stir in the rice. Keep it boiling for twelve minutes by the watch, then pour off the water and set the pot on live coals during ten minutes—the rice is then fit for the table.

His second recipe appears in a letter to his friend Joseph Dalton Hooker (figure 3.1). Sent on February 1, 1871, this letter summarizes Darwin’s...

Nucleic acids and proteins play a central role in life on Earth today. These polymeric biochemicals, composed, respectively, of nucleotides (figure 4.1a) and amino acids (figure 4.2a), provide the catalysis, the genetics, and some of the structure of all living systems. The genetic information in the nucleic acid DNA (deoxyribonucleic acid) is transcribed to the nucleic acid RNA (ribonucleic acid; figure 4.1b), and this information is then translated from RNA to protein. Most contemporary living systems need other polymers as well. Today, for example, the up-to-date organism uses polymers of sugar—carbohydrates—to store energy and build (plant) cell walls....

Organic chemists should have invented the computer scientists’ motto, “Garbage in, garbage out.” Proceeding step by step, purifying the product of one step before using it in the next: this is the orthodox approach to organic synthesis. Under carefully controlled conditions, it is just possible to constrain the chemistry of a pure input compound to give a unique product. But garbage in—an impure compound or a complex mixture of compounds—does as it damn well pleases. And it almost always yields an intractable mixture of products—garbage out.

Unfortunately, all of the most impressive prebiotic syntheses produce garbage by...

We have a fairly clear picture ofhowlife began. Sketched in broad strokes, a six-part scenario is plausible: (1) the genesis in distant stars of the chemical elements crucial to life; (2) the formation of the Solar System and accretion of planet Earth; (3) the nonbiologic buildup in Earth’s oceans of small, simple, organic monomers; (4) the linkage of these monomers into larger, more complicated, polymeric organics; (5) the rise of information-containing polymers; (6) the aggregation and assembly of living cells.

But if the broad strokes are clear, the details are not. We cannot, for example, estimate the likelihood...