Stories in Stone (37 page)

Bacterial-stimulated crystallization most often occurs in nonflowing water, where it produces branching, shrublike growths.
The wee forests often form in ponds and can extend laterally for tens of yards with shrubs growing an inch high, although
they can also skyrocket to three inches in the right conditions.
Some forests even tilt in the direction of water currents.
To extend the forest analogy, inorganic calcite precipitates on and around the shrubs, eventually accumulating deeply enough
to bury the shrubs and to provide a substrate for the next layer of bacterially generated shrubs to develop.
Chafetz and Folk
hypothesized that each shrub layer, or bed, represents one year of deposition with maximum shrub growth in summer and maximum
“snowfall” of calcite in winter.

By cutting the stone perpendicular to the bedding, quarrymen exploited the dense, well-cemented shrub-and-snow texture.
In
ancient times, builders took advantage of travertine’s low compressibility by placing blocks with the beds horizontal.
For
modern travertine used as cladding and not for structural purposes, architects disregard geology and structural integrity
and attach the thin sheets to walls any way that looks good, with the result that bedding planes may run vertically and not
horizontally.

Architects don’t appear to share geologists’ affinity for travertine’s characteristic holey texture, though the voids are
a good place to see where calcite crystals have grown.
When I lead geology-oriented walking tours in downtown Seattle, I encourage
people to use a hand lens to explore the pockets and look for six-sided calcite crystals.
(I have also been known to sprinkle
balsamic vinegar on the crystals.
Geologists more typically use dilute hydrochloric acid to create a reaction with the calcite,
which bubbles off carbon dioxide, but I like balsamic vinegar; it’s always available and has multiple uses.)

Builders don’t like voids because they provide a good spot for pollution-related particulates to collect.
The dirt makes many
buildings with exterior travertine look blotchy, as if they had the bubonic plague.
To counter dust and soot accumulation,
builders often fill in the holes in travertine with grout, which also prevents damage from water pooling, freezing, and expansion.
⁸

Reacting to Chafetz and Folk’s radical shift in explaining how travertine formed, geologists from around the world tried to
verify the Texas geologists’ conclusion.
Within a few years, bacteria had been reported from travertine in Germany, Idaho,
Yellowstone National Park, and Morocco, as well as at other travertine deposits in Italy.
All occurred in warm, chemically
harsh waters.
However, Folk and Chafetz had one significant problem with defending the conclusions in their 1984 paper; they
didn’t see any solid bacterial bodies in Italy, only the voids left behind by decayed bacteria.
What was missing was good
fossil evidence.

Folk returned to Italy in June 1988 to look for more bacteria in travertine.
This time he traveled north of Rome to Viterbo
and the Bagnaccio and Bulicame hot springs, both of which have been well known for their therapeutic waters since Etruscan
times.
⁹
“Bob wanted to pursue what he called the ‘lesser rocks,’ those with complex histories that formed under enigmatic circumstances.
They also happened to be the prettiest,” says his former student Paula Noble, now a paleontologist at the University of Nevada,Reno.
¹⁰

At Viterbo, Noble and Folk collected mud and samples of recently formed travertine.
They also dropped coins and pipes in the
water to test how quickly travertine formed.
On the pipes, travertine precipitated faster in areas hit by sunlight, which
were richer in bacteria.
No travertine accumulated on the copper coins because bacteria don’t like copper.
“He was so excited
to see these examples of how bacteria affected travertine,” says Noble.

When he and Noble returned to Austin, Folk began to examine his samples with an aged electron microscope.
At 5,000
magnification, the most powerful the old scope could manage, he saw beautiful calcite and aragonite crystals.
Folk described
them as “resembling an ear of corn with a tattered shuck enclosing it” and “covered with a forest of spikes like a fakir’s
bed.” The scope also revealed calcified bacteria.
He now had the evidence that had eluded him for many years.
Better material
was yet to come.

In early 1989, the University of Texas acquired a new scanning electron microscope.
The SEM’s 100,000
magnification revealed tiny spheres and bumps studding the calcite.
Folk initially ignored them, as had other SEM researchers,
thinking they were sampling artifacts or lab contamination.
Not all of the samples, however, exhibited the microballs.
In
some samples the spheres clumped together.
He continued to look at the odd balls but also retreated to the library, where
he found descriptions of similar-looking objects that microbiologists called ultramicrobacteria, or dwarf bacteria.
The microbiologists
hypothesized that the dwarf bacteria had shrunk in response to toxic conditions, incompatible temperatures, altered pH, or
nutrient stress.
Upon a return to normal conditions they would revert to their normal size.

Folk questioned the biologists’ hypothesis particularly after seeing an SEM photo from Bulicame in April 1990.
The eureka
photo is mostly gray with a white plane, the top part of the crystal, running from the upper left corner to the bottom right
corner.
Below the plane is a light gray surface dotted with many spheres and one white, sausage-shaped body.
On the left side
of the plane rests an ovoid body, which looks large enough to encompass most of the other spheres.
The ovoid is about twice
as tall as the most unusual shape in the photo—a thin, saguaro-cactus-like body that rises from the center of the plane and
which Folk described as a chain of eight nannobacteria.
The entire shot shows an area 3.5 microns wide by 2.5 microns high,
less than half the size of a red blood cell.

To Folk, these odd little balls and chains closely resembled bacteria shapes, and didn’t look like any minerals he had seen
in his decades of peering through microscopes.
Unlike minerals, which tend to grow together as one mineral and not remain
as single entities, they also clustered in swarms like bacteria in a “feeding frenzy.” The more Folk peered at these unusual
objects, the more he became convinced he was seeing life and neither artifacts nor minerals.
He published his results in 1993
in another landmark paper,
SEM Imaging of Bacteria and Nannobacteria in
Carbonate Sediments and Rocks
.
¹¹
This was the well-illustrated paper that Romanek and crew poured over in trying to understand Martian meteorite ALH84001.

Once he found nannobacteria in his travertine, Folk began to find them everywhere.
They were in cold freshwater spring deposits,
deep underground in caves, in shallow saltwater, and in two-billion-year-old dolomite.
Nannobacteria-generated calcite clogged
a pipe from a hot water heater and scummed a birdbath.
Nannobacteria balls covered corroded iron, copper, aluminum, and lead.
Noncarbonate rocks, such as opal, chalcedony, and chert, also showed a nannobacterial origin.
Unknown to Folk, others had
begun to see nannobacteria, too.

Folk was working in his lab on August 7, 1996, when a colleague rushed in and said “Have you heard the NASA TV conference?
They found nannobacteria in the Martian meteorite.” What Folk’s colleague didn’t tell him was that in describing their nannobacteria,
the NASA team had used a slide showing the nannobacteria Folk had described from travertine at Bulicame.
“Yes, I was excited,
but when their results first came out in the press as photos, my colleague Leo Lynch and I both thought the same thing.
Gee,
their pics look like excess gold coating artifacts,” said Folk.
“Later when they used a thirty-second gold coat, we were convinced
that they did indeed have nannobugs.” When Folk was able to look at ALH84001 under a SEM he found it permeated with nannobacteria.

Not everyone agrees that the Martian meteorite teems with supermicroscopic life.
One scientist I corresponded with e-mailed
me: “The existence of nannobacteria in extraterrestrial rocks (or any other life form, for that matter) is completely UNPROVEN,
in my opinion (an opinion that I think you’ll find to be almost universally shared).” The skeptics’ main concern is that classic
line “size matters.”

Nannobacteria are too small to contain all of the nucleic acids and ribosomes necessary for life.
This was the conclusion
reached by a distinguished panel of scientists in a National Academy of Sciences workshop in October 1998.
Inspired by NASA’s
report of Martian life, the panel sought to establish the smallest size of a free-living organism.
The consensus was that
between two hundred and three hundred nanometers “constitutes a reasonable lower size limit for life as we know it.” Folk’s
smallest nannobacteria are only fifty nanometers wide.

Despite the establishment of this Maginot Line on the minimum size of life, researchers continue to report that they have
found and cultured, or reproduced, nannobacteria-like bodies.
The hottest field at present is in medicine, where researchers
have reported nanoparticles in human, rabbit, and bovine blood.
As occurs in travertine, the nanoparticles appear to generate
calcite that contributes to health problems as diverse as kidney stones, malignant tumors,Alzheimer’s disease, and heart disease.

“At this point we cannot be sure if the nanoparticles are living or not.
Part of the problem is that we haven’t perfected
how to investigate them,” said Virginia Miller, a professor of physiology at the Mayo Clinic.
¹²
In 2004 she was lead author on a paper that examined the role of nanoparticles and atherosclerosis, and in 2006 she co-organized
a conference on pathological calcification, which brought together experts in biology, geology, and medicine.

Although Miller still wavers on whether nanoparticles are living organisms or not, she, like everyone else I talked with,
credited Folk with stimulating her research.
“I think we are at the forefront of something exciting.
I will accept whatever
we find but either way Dr.
Folk’s work has really given us a new way to think about the disease process, at least in regard
to kidney stones and arterial calcification.”

Miller’s comments get to the heart of Robert Folk’s research with travertine, bacteria, and nannobacteria.
Ultimately, it
isn’t critical whether the nanometer-sized particles he sees are living or not.
What is important is the scientific process.
He saw something, travertine in Bernini’s columns at St.
Peters, that intrigued him.
He studied it and published his results,
which raised awareness in others and more questions in him.
He went back out in the field, collected more samples, and took
advantage of technological advances to ferret out additional answers.
He also was persistent, spending hours and hours learning
to use the new technology.
Again he reported what he had found, and he continued to try to better understand and learn about
what he had discovered.