Big molecules from the frozen cores of comets, or from the wisps of dust between stars, could have been the first seeds of life on earth, according to recent speculations by scientists studying the chemical evolution in space and on earth.
The scientists including both chemists and astronomers, are seeking to explain and evaluate the curious fact that highly complex organic molecules -- the precursors of life -- are apparently present in meteorites, comets, and in interstellar dust.
There are currently far more theories than there is agreement.
At the fifth annual conference on the chemical evolution of life, held recently at the University of Maryland, noted astronomer Fred Hoyle presented through a colleague, a paper suggesting that life itself in the form of bacteria, and not just precursor chemicals, is scattered everywhere in the universe. Equally famous astronomer Fred Whipple, in person, declared the whole idea of life from space "utter nonsense."
Among the most interesting of the laboratory work presented, was from May Greenberg of Leiden University in the Netherlands. Greenberg built a small system to mimic the grains of interstellar dust and their cold environment.
The particles, averaging about a 50,000th of an inch across, exist in the clouds that give galaxies and nebula their foggy appearance. They are believed to have rocky silicate cores with some carbon, nitrogen, oxygen and hydrogen scattered on the surface.
Greenberg cooled a one-inch chamber to within 10 degrees of absolute zero -- the temperature at which even the wobbling of atoms stops -- and injected into the chamber a dombinating of chemicals in the form of a gas, supposedly identical to that on the grains in space. And he inserted a tiny gloss rod, to mimic the silicate core of a space particle.
He found that the chemicals clung to this "cold finger," as he called the glass rod.
And since the grains in space receivee occasional blips of light radiation coming from stars, Greeberg slowly bathed the "cold finger" and its accumulated chemicals with ultraviolet radiation. Each hour of radiation in the lab gave the equivalent of what a grain in space would recieve in a thousand years, a brief time on a cosmic scale.
Remarkably, Greenberg found that even though the atoms were all but frozen into immobility, the small amount of radiation was significant to set off occasional tiny bursts of chemical reaction. The reactions caused a rise of five of 10 degrees Kelvin (a scale on which zero is -523 Fahrenheit), and sometimes even little flashes of light.
The result was that the simple chemicals built up to more complex ones. As the process went on, through repeated cycles of reacting then cooling, as it does in interstellar grains over 50,000 or 100,000 years, large complex organic molecules evolved. Greenberg thinks, though the chemical analysis is not complete, that he will find polypeptide chains -- the chemical step just before the emergence of life.
The link between this material and life on earth could come two ways. First, since comets are made by simply piling together millions of these interstellar grains, some comet passing close to the earth may have deposited a large amount of these highly complex organic molecules, together with some of the frozen water molecules that make up the grains and the comet, on the barren, dry earth as it possibly existed 4 billion years ago.
Alternatively, the interstellar grains could have seeded the earth as the planet passed through the thick bands of them in the dusty spiral arms of our galaxy. This happens every hundred million years as the earth makes its regular orbit through the Milky Way. Thus, at regular intervals as the earth was forming, the molecular seeds could have been deposited in fairly large numbers upon it.
These scenarios are only speculation laid on top of Greenberg's work, and still are rated as less likely than the theory that the complex organic molecules needed for life were formed on earth.
One problem with this theory, however, is that recent discoveries have pushed the apparent beginning of life farther and farther back, closer and closer to the time the earth was formed, leaving very little time for complex molecules to have evolved on the planet.
However, even though the seeding theory might solve this problem, said Cyril Ponnamperuma, conference host and researcher on the origin of life, the other theory remains the simplest and most direct, and it is possible that the big organic molecules were able to form on earth in the relatively short time between the formation of earth 4.5 billion years ago and the appearance of life about 3.8 billion years ago.
Ponhamperuma said he now believes in what he calls "instant life" -- that the chains of molecules necessary for life could form very quickly once water was vented from the interior of the earth at some early date in its history.
The motion presented last week that is judged to be least likely among all the theories is Hoyle's idea, which he calls "panspermia." He believes that frozen bacteria inhabit the interiors of the interstellar dust grains, and on the insides of comets are teeming in the warmth and melted ice that might be caused by radioactivity from elements in the comet walls.
If Hoyle's theory is true, the bacteria would have to be formed and survive under extraordinary conditions as the comets and dust went about their seeding of the universe.