Science: Life Begins

“Life is not a miracle,” says Nobel Prizewinning Chemist Harold C. Urey. “It is a natural phenomenon, and can be expected to appear whenever there is a planet whose conditions duplicate those of the earth.”

Such planets cannot be rare, said Urey last week in a lecture at the New York Academy of Medicine. According to a star census taken by Astronomer Gerald P. Kuiper of the University of Chicago, there are 100 billion stars in the Milky Way galaxy, and one star in each thousand is believed to have planets circling around it. So there must be 100 million “solar systems” in the earth’s galaxy alone.

Not all these planets are suitable for life. Some are too hot; others are too cold, or otherwise inhospitable. But Scientist Urey believes that many are seedbeds for the sprouting of life.

The atmosphere of a pre-life planet, Urey believes, is not like the earth’s. It is highly “reducing”: i.e., it contains large amounts of methane, ammonia, water vapor and similar compounds, but no free oxygen. The atmospheres of Jupiter and Saturn are believed to be like this. As millions of years pass, the sun’s light causes chemical reactions among the atmospheric gases. Larger molecules begin to form (e.g., aldehydes, amines, organic acids), and they rain down into the oceans below. There they react with one another and with dissolved salts. All possible chemical compounds are formed eventually, and the ocean becomes a rich solution of them.

After a billion or so years of such pre-life evolution, theorizes Urey, the blind forces of chemical attraction accidentally create a single molecule which has the ability to absorb other molecules and create a replica of itself.

This molecule is alive, for the great test of life is ability to reproduce. It has no living enemies. Swiftly it multiplies, feeding on the nutritious chemicals in the ancient sea. Soon the water is populated with hungry molecules, which differentiate swiftly into many types.

At last one of them learns to extract energy from the sunlight, releasing oxygen into the air and absorbing carbon compounds. When these living forms—the first plants—have multiplied for a few million years, they create the oxygen-rich atmosphere that the earth now knows. Then oxygen-breathing plant-eaters evolve to devour the plants, and the full stream ot evolution is under way.

Dr. Urey has no tangible proof of this theory. But he is hopeful of two investigations now in progress. One, conducted by one of his students at the University of Chicago, is to expose a synthetic reducing atmosphere of methane, ammonia and water vapor to ultraviolet rays If organic compounds are formed, it will be proof that they could be formed in the atmosphere of a pre-life planet.

The other proof is being sought by studying Titan (one of the satellites of Saturn), which is somewhat bigger than the moon. Titan is too cold for life as the earth knows it, but it has an atmosphere containing much methane. Chemist Urey hopes to find that sunlight is slowly making organic compounds out of this simple gas. If Titan were warmer and bigger the process might already have clothed it with oxygen—and life.