In the latest scientific version of Genesis, life begins, paradoxically, with an act of destruction. After 10 billion years of guzzling the hydrogen in its core, a sun-size star runs out of nuclear fuel and becomes unstable. It goes through a series of convulsions and expels a shell of searing-hot atoms—including hydrogen, carbon, and oxygen. The star fizzles into an inert cinder, and its atoms drift off, seemingly lost in the interstellar gloom.
But next the story takes a surprise turn, from destruction to construction. Some of those rogue atoms float into a nearby gas cloud and stick to fine grains of dust there. Even at a frigid –440 degrees Fahrenheit, the atoms bump and crash into each other, merging to form simple molecules. Over millions of years, one relatively dense region of the cloud begins to collapse in on itself. An infant star takes shape at the center. In the surrounding areas, temperatures rise, molecules evaporate from their icy dust grains, and a new round of more intricate chemical reactions begins.
Then comes the most wondrous part of the whole tale. Those reactions weave the simple atoms of hydrogen, carbon, and oxygen into complex organic molecules. Such carbon-bearing compounds are the raw material for life—and they seem to emerge spontaneously, inexorably, in the enormous stretches between the stars. “The abundance of organics and their role in getting life started may make a big, big difference between a giant universe with a lot of life, and one with very little,” says Scott Sandford of NASA’s Ames Research Center in Moffett Field, California, who studies organic molecules from space.
The notion that the underlying chemistry of life could have begun in the far reaches of space, long before our planet even existed, used to be controversial, even comical. No longer. Recent observations show that nebulas throughout our galaxy are bursting with prebiotic molecules. Laboratory simulations demonstrate how intricate molecular reactions can occur efficiently even under exceedingly cold, dry, near-vacuum conditions. Most persuasively, we know for sure that organic chemicals from space could have landed on Earth in the past—because they are doing so right now. Detailed analysis of a meteorite that landed in Australia reveals that it is chock-full of prebiotic molecules.
Similar meteorites and comets would have blanketed Earth with organic chemicals from the time it was born about 4.5 billion years ago until the era when life appeared, a few hundred million years later. Maybe this is how Earth became a living world. Maybe the same thing has happened in many other places as well. “The processes that made these materials and dumped them on our planet are universal. They should happen anywhere you make stars and planets,” Sandford says.
