How, then, did wisps of gas and specks of clay come to life? Last week 405 researchers gathered in Barcelona for the International Conference on the Origin of Life to offer some answers. Carl Sagan and colleagues reported on organic molecules in the atmosphere of Saturn’s giant moon Titan, which hints that the solar system is full of the ingredients of life; others gave papers on how comets might have seeded Earth with life and how molecules teamed to replicate themselves. No one has worked it all out, but they may have made progress by moving sideways-asking not how but where life was born. Lerman lofted one intriguing trial balloon. Or trial bubble. He suggested that frothy, filmy, iridescent bubbles of seawater served as life’s delivery room.
Chemists thought they had the puzzle all figured out years ago. In 1953, Stanley Miller of the University of Chicago zapped a mix of water (to simulate the oceans) and hydrogen, ammonia and methane (the atmosphere) with electricity (to simulate lightning). After a few days he harvested some yellowish-brown glop that turned out to contain amino acids, molecules that string together into proteins like beads in a necklace. Proteins are one of the two basic ingredients of life. The other is nucleic acids like DNA, and experiments similar to Miller’s managed to make them, too. But recently, geologists concluded that the early Earth had nothing like the atmosphere in Miller’s flask. Then theorists stepped in. Maybe clay turned inanimate gunk into life: perhaps volcanoes or deep-sea hydrothermal vents provided the spark of life. But these ideas all fell short. Although some of the proposed chemical reactions do produce complex organic compounds including amino acids, they aren’t exactly a bumper crop. And that’s a problem: a smidgen of amino acids created on a bed of clay over here would never meet up with the other organic molecules necessary for life.
Lerman’s bubbles could bring the ingredients together. In his model, bubbles floating on the ocean trap carbon-containing molecules, bits of clay and metals sprinkled in the atmosphere by volcanoes or delivered by comets (diagram). When the bubbles popped, they left behind droplets rich in the precursors of life that Miller’s flask and other experiments show can breed DNA and amino acids. From these concentrated chemicals, ultraviolet radiation or lightning sparked the creation of complex molecules-amino acids, parts of DNA and RNA, fatty acids-that fell to Earth and, maybe, formed the first living cell. None of the chemical steps is new, Lerman emphasizes; his bubbles merely provide a way for them to happen. “it may not have been a global primordial soup which was key to chemical evolution,” he says, “but the primordial bubble.”
Bubble or comet, deep-sea vent or volcano, wherever the ingredients of life first evolved, combining them into something fully alive still seems madly improbable. Fred Hoyle, the British astronomer, once said the event is about as likely as assembling a Boeing 747 by sending a whirling tornado into a junkyard. This is the hitch: life requires both DNA and proteins. DNA cannot pass on genetic information without proteins. And proteins cannot form without DNA, since it contains the instructions for stringing together amino acids. It’s a classic chicken-and-egg problem. And it seems so intractable that some leading researchers, notably Francis Crick of the Salk Institute (and “double helix” fame), have suggested that life-not the ingredients of life, but something fully alive–arrived from space 3.5 billion years ago, That, of course, merely pushes the question of life’s origins to another planet. But it explains why NASA has been in the origin-of-life business for years: perhaps a discovery on Mars, or in interstellar space, could crack the whole mystery.
Lerman and origin-of-life theorist Sherwood Chang of NASA’s Ames Research Center in Mountain View, Calif., plan to generate bubbles in a special chamber to test whether they could work as the birthplaces of life’s molecules. Even if the answer is yes, the best that researchers can hope for is a definite “maybe.” Life could have begun with sea bubbles. But short of a time machine into the distant past–and just think if they go back too far–scientists will probably never be sure whether it really did.
According to a new theory, life began when organic molecules, clays and metals concentrated on the surface of sea bubbles. Lightning sparked chemical reactions that produced the complex molecules of primordial life.
Air and sea mix, making bubbles.
Clays, metals and organic molecules from volcanoes and comets stick to the bubbles.
When the bubbles burst, concentrated molecules are released into the atmosphere.
Lightning trigger chemical reactions that form more complex molecules.
Chemical mix returns to earth in rain or snow.
