Building blocks for life may have come from outer space
BY JEFF FOUST
Posted: January 30, 2001
In a paper published Tuesday in a special issue of the journal Proceedings of the National Academy of Science, researchers from NASA's Ames Research Center and the University of California Santa Cruz said conditions in the early solar system were ripe for the formation of critical organic compounds and even cell-like structures, although they stopped short of saying that life itself originated in outer space.
Scientists took a mixture of simple ices, including water, carbon dioxide, carbon monoxide, and methanol and cooled it to just ten degrees above absolute zero. That supercold ice mixture was then exposed to strong ultraviolet radiation to mimic conditions in the dense molecular clouds from which solar systems form.
While scientists expected that the ultraviolet radiation would create new, more complex chemicals within the ice, the amount and complexity of the new compounds surprised them. "Sure, we expected that ultraviolet radiation would make a few molecules that might have some biological interest, but nothing major," said Lou Allamandola, a NASA Ames scientist. "Instead, we found that this process transforms some of the simple chemicals that are very common in space into larger molecules which behave in far more complex ways, ways which many people think are critical for the origin of life, the point in our history when chemistry became biology."
Not only could such chemicals provide the raw materials for the formation of life, they may have helped provide the structure for the first cells, according to another member of the team. "Upon the addition of liquid water to the organics produced during ice irradiation, some of these new compounds, with no outside help, organize themselves into tiny vesicles with complicated structures," said Jason Dworkin, a SETI Institute researcher and lead author of the journal paper. Vesicles are hollow droplets that resemble cells in size, shape, and structure, but have inorganic origins.
Dworkin noted that the vesicles included other chemicals, including one that converted ultraviolet light into visible light. "Molecules that do these things are thought to be extremely important for the origin of life," he said. "Membrane structures are necessary to separate and protect the chemistry involved in the life process from that in the outside environment, and all known biology uses membranes to capture and generate cellular energy."
"Membranes are like a house," Dworkin said. "Maybe these molecules were just the raw lumber lying around that allowed origin-of-life chemicals to move in and set up housekeeping or construct their own houses."
Some members of the team are keeping an open mind to the issue of the origins of life. "We are just now beginning to realize that we are only seeing the tip of the iceberg in terms of extraterrestrial molecular complexity," said Allamandola. "I know I hold a minority view on this nowadays, but I suspect that even deep inside a comet, which is mainly water ice after all, reactions are much further along than we think and the chemistry quite complex."
The discovery also raises the prospects of the formation of life in other solar systems. Irradiation of ices "happens all the time in the dense molecular clouds of space," said Allamandola. "Very complex organic molecules that might be important for the origin of life could well be falling on the surfaces of newly formed planets everywhere in the univers... This discovery implies that life could be everywhere in the universe."