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Winter 1997

Research Magazine > ARCHIVE > Winter 97 > Article

Alone in the Universe?
By Judy Bolyard Purdy

A chance encounter in a NASA hallway led geochemist Chris Romanek to examine what may be the find of the century.

Romanek, a researcher at UGA's Savannah River Ecology Laboratory, was working at the Johnson Space Center in 1993 when NASA scientist David Mittlefehldt asked him to take a look at some "interesting orange patches" on a potato-sized rock. Earlier that year, Mittlefehldt had classified the rock as a meteorite from Mars.

The orange patches turned out to be carbonates, and on Earth, most carbonates, such as limestone and marble, form in the presence of water. The meteorite's carbonates are the first of a handful of compelling clues that life may have existed on the red planet 3.6 billion years ago.

"I knew the [orange] features that Mittlefehldt showed me contained clues about low-temperature [carbonate] processes on the surface of Mars," said Romanek, who specializes in carbonate chemistry. "Liquid water doesn't occur in many places in the solar system. The meteorite has characteristics that indicate aqueous processes aided in the precipitation of these carbonate minerals.

Shortly after their chance meeting, Romanek published a report in the journal Nature, stating that the carbonate "globules" were formed on Mars from warm, carbonated waters. Although no hints of life could be gleaned from the work, he said he knew at the time these waters also were capable of sustaining biological reactions.

"This was an exciting finding, especially given an age date for the globules of 3.6 billion years, which is the time [many scientists] think liquid water flowed on the surface of Mars," Romanek said.

The 4.5 billion-year-old meteorite, which is one of only 12 known Martian meteorites, was blasted off Mars' surface by a massive collision about 16 million years ago. It traveled through space until 13,000 years ago, when it was captured by Earth's gravity and landed in the South Pole region. There it lay until December 1984 when geologist Roberta Score plucked it off the ice during an NSF-funded meteorite collecting trip to the Antarctic. A dozen years later, the meteorite, named ALH84001, was catapulted into world headlines when a nine-member research team that included Romanek published its findings of possible life on Mars.

After determining the carbonates had formed at temperatures capable of sustaining life, Romanek next used acid to remove the top layer of globules - which are about 200 microns in size, or about the width of a human hair - so he could view them with a scanning electron microscope (SEM). It was then that he observed strange, tubular features entombed in the carbonate globules.

"It was quite astounding because features like this haven't been found in other meteorites," he said. "They looked very similar to fossilized bacteria found in limestones formed on Earth. So I took my SEM pictures of the meteorite to [colleague and mentor] Everett Gibson and asked if he could distinguish them from fossilized bacteria entrapped in terrestrial limestones."

Gibson, a meteorite expert at NASA, realized Romanek's pictures merited the attention of David McKay, an authority on electron microscopy at the space center. McKay had access to a highly sophisticated SEM that can magnify objects 150,000 times. When McKay viewed the samples, he too saw the distinct structures with outlines that resemble bacteria.

The fossil-like structures are very small - one-tenth the size of the oldest fossils found on Earth. "These entities are many, many times smaller than the size of the carbonate globules," Romanek said. "In fact, if you make a globule as large as the Atlanta-Fulton County Stadium, these little entities would be about the size of a hot-dog."

Many scientists believe that long ago Mars may have had the climatic conditions to support primitive life. The fossil-like structures have the greatest potential to substantiate the presence of life on Mars. Ironically, they also are the most controversial evidence. Are they real fossils or just some quirky inorganic formation? No one knows - yet.

The research team says its findings, which also include the first evidence of potential "biominerals" and organic compounds on Mars, offer intriguing evidence that microscopic life might have existed in the meteorite's cracks and crevices 3.6 billion years ago, long before it was hurled into space.

The team, which began as a trio of Romanek, Gibson and McKay, enlisted the help of six other scientists, including Kathie Thomas-Keprta, a transmission electron microscopist on loan to NASA from Lockheed Martin. Thomas-Keprta examined certain mineral deposits, which are so tiny a billion of them could easily fit on the head of a pin (or, using the hot-dog analogy, would be about the size of pickle slices). She determined that the chemistry and structure of these minerals resembled biomineral deposits commonly produced by bacteria on Earth.

Thomas-Keprta invited her colleagues Richard Zare and Simon Clemett at Stanford University to use a sophisticated laser mass spectrometer to analyze the rock for organic molecules.

The high-tech equipment can peel back layers of carbonate one molecule at a time. When they did, the Stanford researchers discovered PAHs (polycyclic aromatic hydrocarbons), the first organic compound ever detected on Mars. The PAHs were strongly concentrated in the carbonate globules, another indication of life.

PAHs commonly are produced when organisms die and decay, but they also are present in engine exhaust, cigarette smoke and barbecued foods. Some scientists speculate the meteorite's PAHs were caused by earthly contamination. But the low concentration of PAHs on the rock's surface compared with their higher concentration inside the carbonates suggests they are not the product of contamination.

"Rather, the Stanford researchers showed that these PAHs are indigenous to the meteorite," Romanek said. "The presence of all these various chemical and mineral deposits being in one place is uncanny. This close association raises the possibility that the globules were formed by biological processes."

The team, which also included a scientist from McGill University, published its startling findings of potential life on the red planet, last August in the journal Science.

"If you look at all these [findings] individually, they can be explained inorganically," Romanek said, "but if you take them all together, they are consistent with biologic activity."

There is still lots of data to collect from the 4-pound rock, more than one research team can handle. And it's a good thing because the team's findings have revived an interest in meteorites, and now more and more scientists are clamoring to get their hands on a piece of the rock.

The researchers also want to explore concerns raised by other scientists who "want us to find cell walls or demonstrate the tubular structures have an inside and outside," Romanek said.

That's a tall order because the fossil-like structures are so small. Nevertheless, the researchers are trying to develop a procedure that will enable them to slice open the structures and peer inside.

No doubt they also will be spending a lot of time reading and evaluating other scientific studies that support or refute the interpretations they set forth in Science. Two papers already have been published this year that question the team's interpretation about contamination issues and formation temperatures. One contends that the PAHs are a result of earthly contamination, and the other suggests that the biomineral magnetite was formed at a temperature too high - almost 1500 degrees Fahrenheit - to sustain life.

"We've looked at their data and we do not waiver in our interpretations," Romanek said. "These recent studies have alternate interpretations, just as our original paper does. Only time will tell whether we are right or not, and this will not happen overnight."

Even with the recent skepticism, the research already has changed our view of the cosmos. Perhaps the processes that gave rise to life on Earth also occurred on other planets. The age-old question of life on Mars continues to intrigue us all.

"This story thrills some and chills some, but it fascinates everyone," Romanek said. "You'll have to see our evidence and make up your own mind about whether life existed on Mars."

For more information, access http://cass.jsc.nasa.gov/pub/lpi/meteorites/life.html.

Time Line for Martian Meteorite

4.5 billion years ago
our solar system forms
the meteorite forms as a rock on Mars

3.5 billion years ago
carbonate globules form on Martian rock
bacteria fossils form in Australia and South Africa

16 million years ago
a massive collision on Mars hurls the rock into space
on Earth, mammals such as primates, elephants and rodents are evolving rapidly

13,000 years ago
the meteorite, captured by Earth's gravitational field, lands in Antarctica
humans are learning to plant crops

the meteorite is collected in the Allan Hills area of Antarctica

rock is classified as Martian in origin
Romanek, et al., begin analyzing rock's features

Romanek, et al., publish their findings that life may have existed on Mars in the journal Science


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