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
"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
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
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
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
"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
16 million years ago
a massive collision on Mars hurls the rock
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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