From particles on meteorites, a new clue to the origin of organic life
Meteorites from interplanetary space bring to Earth tantalizing chemical clues to the origin of organic life. But, while chemists find such pre-life materials as amino acids (which are building blocks of proteins, or the bases that form units of the genetic code), they have been unable to explain how these crucial compounds have arisen.
Now Thomas J. Wdowiak and David G. Agresti of the University of Alabama report the presence of tiny particles of magnetite in a meteorite that fell near Orgueil (pronounced ''or-gay''), France, May 14, 1864. These particles could have been the catalysts that encouraged the chemicals to form.
The magnetic particles are tiny - generally less than 30 billionths of a meter in diameter, which is more than 10 times shorter than typical wavelengths of visible light. As the scientists explained recently in Nature, this suggests they were produced chemically in a wet environment. They are not dust ground down from larger fragments.
The meteorite, Wdowiak says, ''was probably as wet as beach sand.'' He adds that the energy that kept water in a liquid state ''could also have caused a chemical reaction to begin forming molecules of a pre-life nature.'' The Orgueil meteorite is 3.5 percent organic material, which includes amino acids. Such pre-life chemicals have been found in other meteorites.
Also, a little over a year ago, Cyril Ponnamperuma announced that the Murchison Meteorite contains all five of the bases that combine in different ways to encode genetic instructions. The meteorite fell in Australia 15 years ago. Pon-nam-pe-ruma, who heads the University of Maryland's Laboratory of Chemical Evolution, noted at the time that his laboratory had also been able to create these bases all in a batch by running electrical discharges (miniature lightning bolts) through a gas mixture of methane, nitrogen, and water, such as might have characterized Earth's primitive atmosphere. He observed: ''These results tell us that chemical evolution, the natural creation of life chemicals, is a very reasonable process. They suggest that life elsewhere in the universe is more likely, and they provide a clearer understanding of the origins of life on Earth.''
Something like 19,000 meteorites weighing 0.1 kilograms (about 2 pounds) and up fall every year - 830 weigh 10 kilograms (22 pounds) or more - according to a study published in Science last March. About 2 percent of these are the so-called carbonaceous variety, containing up to 5 percent carbon, in which pre-life chemicals are found.
These meteorites are considered to be samples of the primordial nebulae from which the sun and planets formed. The fact that they carry pre-life compounds today suggests that they may have seeded Earth with these important chemicals soon after the planet formed. At least, they show that chemical processes similar to those which many scientists think may have led to life on Earth have occurred elsewhere in the solar system. Indeed, Wdowiak speculates that ''instead of a pond on primeval Earth, life could have had its earliest beginnings in the warm, wet interiors of large rocks not dissimilar to the Orgueil meteorite.''
Scientists have reached what James P. Ferris of Rensselaer Polytechnic Institute calls a ''watershed in the laboratory study of the origin of life.'' Writing recently in Chemical and Engineering News, he noted that they have extensive knowledge of how life's simple precursors might have arisen. The challenge, now, is to learn how these combined into more complex structures that could lead to living organisms.
This kind of knowledge is not likely to come easily or quickly. But, as they move forward toward that goal, scientists can gain confidence from knowing that pre-life chemical evolution is probably not unique to Earth. It appears to be characteristic of the solar system generally and, perhaps, even of the universe.