Mankind has gazed at the night skies since the dawn of time and wondered, "Are we alone?"

Scientists have renewed hope that the answer is "yes," in the wake of NASA's recent announcement that carbonates found in a Martian meteorite sample appear to have an organic origin.

The sample, called ALH84001, was found in 1984 in the Allan Hills of Antarctica during an annual expedition by the National Science Foundation's Antarctic Meteorite Program.

The meteorite was studied by University of Arizona's Lunar and Planetary Laboratory in 1994.

At that time, three LPL researchers, David Kring, Dolores Hill and James Gleason, analyzed the bulk composition of the meteorite, searching for clues about Mars' volcanic activity and interior mantle.

Although the Planetary Sciences Department studied and retained samples of this meteorite, they were not looking for signs of life, Kring said.

"We were interested in geologic history, whereas this other group (NASA-Stanford) was looking at the origin of the carbonate," he said.

"I think the findings are interesting, but a lot of work will be needed to confirm them. Many questions remain, such as 'were those contaminants picked up in Antarctica?'"

The NASA team found several pieces of evidence that, when considered together, suggest that life may have existed on Mars 3.6 billion years ago, Kring said.

The sample is 4.5 billion years old, which makes it the oldest of 12 meteorites known to be from Mars.

While the meteorite itself is 4.5 billion years old, the carbonates that suggest life are only 3.6 billion years old. The difference is due to Mars' geologic history, Kring said.

Mars today is a seemingly desolate planet of swirling winds, volcanic peaks and dry canals. At first glance, it could be the view seen while driving from Tucson to Phoenix. However, it was a very different landscape 3.6 billion years ago, Kring said.

Computer modeling shows that water probably flowed on or under its surface several times throughout its history - including 3.6 billion years ago. The Martian surface also endured ages meteor bombardment, which cracked surface rocks and later sent them hurling toward Earth.

The sample ALH84001 began as one of these rocks, falling to Earth about 13,000 years ago. While still on Mars, subsurface water flowed up into crevices, solidifying into the carbonate globules researchers now believe may contain the remnants of life.

The carbonate section being studied is microscopic. The largest possible fossil is only 1/1000th the diameter of a human hair.

Some discoveries that sparked the excitement are:

• Worm-like features that could be fossils of very primitive microorganisms.
• Carbonate globules composed of magnetite and pyrrhotite, two minerals that on Earth are produced by bacteria.
• The globular structure itself is consistent with biological origins.
• Polycyclic aromatic hydrocarbons, or PAHs, which are often the remnants of decomposed organic matter. However, they aren't necessarily biogenic, cautioned Kring. PAHs are also found in coal and petroleum on Earth and can be common air pollutants, according to a NASA press release.

"The theory is very provocative, but not conclusive yet," said Robert Strom, professor of planetary sciences at the UA Lunar Planetary Laboratory. "This requires irrefutable evidence."

Holes still remain in the theory, he said.

First, the temperature of the meteorite at formation needs to be discovered. If the temperature was near 700 degrees Celsius, it was too hot for biological organisms. However, if the temperature was between zero and 80 degrees Celsius, life was possible.

Second, "the worm-like imprints may or may not be fossils," Strom said. "The samples will need to be cross-sectioned to reveal the internal structure. If this yields a clay-type structure, it's not life. If it yields an organic structure, then the evidence is pretty conclusive (for life)."

The NASA-Stanford teams did a cross section, but the results haven't been reported yet, Strom said.

"If these samples are remnants of past life on Mars, this is probably the most important discovery ever," Strom said.

The NASA-Stanford teams will continue to analyze the samples, modifying their instruments slightly to search for amino acids (the building blocks of life), said David Salsbury, a spokesman for the Stanford team. More conclusive evidence should be available in one to two years, he said.

The UA is actively involved with Mars research. Lunar and planetary science researchers are involved with the Pathfinder mission to Mars, set for launch in December. William Boynton, professor of planetary sciences, plans to study mineral temperatures on Mars in 1998, as part of the Mars Observer Mission.

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