Considerable evidence exists that a Martian meteorite found on Earth contains fossilized remains of microbial life, a member of the research team investigating the meteorite told a Cornell audience Monday afternoon.
But that evidence does not prove that life existed on Mars in the distant past, said Richard N. Zare, a Stanford University chemist. And if it did exist, that still does not answer the question of where life began -- on Earth, or Mars or elsewhere.
After displaying and explaining the research team's
evidence, Zare told his audience: "Taken
together, they suggest primitive life existed on early Mars." However, there is still
considerable debate within the scientific
community, as each of the individual pieces of
evidence have come under criticism, he said.
Zare's talk, the Harry S. Kieval Lecture in Physics, was titled "Laboratory Measurements of Extraterrestrial Visitors" and was delivered to a standing-room-only crowd in Schwartz Auditorium of Rockefeller Hall.
Chairman of the National Science Board and a member of the National Academy of Sciences, Zare was a member of the NASA-Stanford research group that reported last year that Martian meteorite ALH84001 contains fossilized evidence of microbial life. Zare's chemistry laboratory provided the technique, called laser mass spectrometry, for analyzing the meteorite and identifying its components.
The fact that pieces of Mars come to Earth regularly was proposed by Cornell's Joseph Burns, professor of theoretical and applied mechanics and of astronomy, last March -- before Zare's team published its results in the Aug. 16 journal Science. Zare learned of Burns' work reading The New York Times, and he put a copy of the story on the screen as he delivered his lecture.
One piece of evidence for life on Mars on which many scientists agree, is that Mars is a likely candidate to have harbored life-forming conditions. That is, "long ago, Mars was warm and wet," Zare said. The planet's Olympus mons, the largest volcano in the solar system, shows that to be true.
But more important, the gas and nitrogen trapped inside the meteorite closely match that of the Martian atmosphere, as recorded by NASA's Viking landers in the 1970s. Coupled with an abundance of rare-Earth elements and a high degree of oxidation, Zare said, "You really have telltale signatures, and they all match up."
Among the most compelling evidence: an abundance of carbonate spheres, similar in size and texture to materials produced by bacteria on Earth. The meteorite is volcanic, or igneous, rock, which would have no carbonate in it. "How did it get there?" Zare asked, indicating that biological material may have been responsible.
Another key piece of evidence: the presence of PAHs, or polycyclic aromatic hydrocarbons, associated with life. "This is what you get when you fossilize living matter," Zare said, adding, "Finding PAHs by themselves is not finding life. But it's permissive of life. Some have said these are not PAHs, but I know they are PAHs that we're looking at."
Zare concluded by telling the audience to continue to be skeptical. "As a scientist, you have to maintain skepticism or you become a believer. As a believer, you stop being a scientist."
The research has had other benefits, Zare said. "It shows us that the American people really are interested in science. Prior to this, if you talked about extraterrestrial life, you were considered a nut. Now, it's respectable to talk about it."