Looking for Signs of Life

Clues are found in rocks, a meteorite and space

How --and when --did life begin? Cyril Ponnamperuma, 55, a Ceylon-born geochemist at the University of Maryland, has been seeking answers to this question for much of his career. He has created precursors of life in laboratory simulations of the earth's primitive atmosphere and while with NASA in 1970, identified amino acids (the building blocks of protein) in the Murchison meteorite, which had fallen in Australia a year earlier. Last week, at a meeting of the American Chemical Society in Washington, Ponnamperuma presented three new pieces of evidence that the processes leading to the formation of life can take place in diverse and inhospitable environments:

>Analyzing material from two meteorites found in Antarctica, where they had been frozen in ice for 200,000 years, Ponnamperuma and his colleagues discovered many amino acids, about half of them different from any that are found in living organisms. Two facts convinced him that the acids are, in his words, "extraterrestrial and pre-biotic": 1) Unlike the Murchison meteorite, which had been contaminated by earthly organic matter after it fell, the Antarctic meteorites were pristine, containing only the amino acids they brought to the earth from space.

2) When polarized light was passed through solutions of water and some of the amino acids, it was deflected to the right. "In all the '20 amino acids we know of on earth," says Ponnamperuma, "the polarized light turns to the left." But, he adds, "In all the pre-biotic experiments conducted in our laboratory, we got both lefthanded and righthanded amino acids." His conclusion: the amino acids are not due to terrestrial contamination, but to pre-life forms that evolved somewhere in space.

> Examining 3.8 billion-year-old rocks found in Greenland's Isua (Eskimo for "the farthest we can go") region, Ponnamperuma and other scientists found evidence of compounds called hydrocarbons, which are of major importance in organic chemistry. To discover whether these hydrocarbons had a biological origin, scientists analyzed the ratio of two isotopes, or forms, of carbon. They found that the amount of carbon 12, the isotope most utilized in biological processes, was high in relation to carbon 13. This indicates that the hydrocarbons were produced by photosynthesis, the process by which plants convert carbon dioxide into organic compounds and oxygen. Ponnamperuma's find shows that life was present on earth 3.8 billion years ago, when the planet was only 800 million years old. The oldest previously known terrestrial life dated back 3.4 billion years.

> In an attempt to determine whether organic molecules can form on other planets, scientists at Ponnamperuma's Laboratory of Chemical Evolution filled a container with gases like those in the atmosphere of Jupiter. Then, to simulate sunlight and Jovian lightning flashes, they exposed the gases to ultraviolet light and shot electric discharges through them. The brown and yellow hues of the organic compounds that formed in the container closely resemble those in the spectacular pictures of the Jupiter clouds taken by the Voyager 1 and 2 spacecraft, which flew by the planet earlier this year. This finding strongly suggests that organic compounds also exist on Jupiter. .

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