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26 A New Era building blocks of life’s chemistry; scientists proved in 1970 that a meteorite unambiguously contained extraterrestrial amino acids.* Researchers have demonstrated that the spontaneous generation of amino acids in interstel- 21s : a a lar space is possible. Many scientists once assumed that not even the earliest steps in the chemistry of life could take place in space because ultraviolet radiation from stars would break up organic molecules. Now it appears that such chemistry can begin in the dust grains of interstellar clouds, at least those that are sheathed in ice. Higher carbon clusters, formed in the out- flows of carbon stars, can survive passage through the interstellar medium. Crucial early processes appear to take place in space long before planet formation, making it possible for asteroids, comets, meteorites, and inter- planetary dust to deposit complex organic material on early planet surfaces.* Hopes for finding simple life on Mars still were high in 1965 when the Mariner 4 spacecraft began sending back our first close-up images of the red planet. Our expectations suffered a blow when those pictures showed a cratered, Moon-like desert. We later learned that Mariner 4 had imaged some of the bleakest parts of Mars; subsequent missions revealed more intriguing features. Nonetheless, the disappointment ran deep. There remained the possibility that microorganisms might survive such harsh conditions. The Viking landers that reached the Martian surface in 1976 carried on-board laboratories to look for evidence of biological pro- cesses. Gilbert Levin, the designer of one of the experiments, believed that Viking had found evidence of life, but most scientists disagreed. Some drew sweeping conclusions from our failure to find confirmed evidence of life on Mars. “It is now virtually certain that the earth is the only life-bearing planet in our region of the galaxy,” wrote biologist Norman Horowitz. “We have awakened from a dream. We are alone.”* Others have questioned such negative declarations. Since Viking, we have discovered that billions of years ago—when life on Earth was getting its start—enough water pooled on the surface of Mars to allow the possibil- ity of living things. Many forms of Earth life could have survived and even thrived under those conditions. However, the Martian environment took a different path than Earth’s, one too stressful for any known form of life to survive on the planet’s surface. Mars life may have appeared early, only to be extinguished within the planet’s first billion years.° Might there still be life under Martian rocks and dust, drawing on sub- terranean water? Biologist Hubertus Strughold (sometimes called the father of space medicine) proposed 40 years ago that living things might Disappointment and Revival