The Rock From Mars (33 page)

Andrew Steele moved across an ocean to work on the Martian meteorite, and found evidence that others had missed. (Kjell Ove Storvik/AMASE)

Kathie Thomas-Keprta is shown with a transmission electron microscope in Building 31. She and coworkers generated renewed headlines and rebuttals in early 2001, when they published new research on the mysterious magnetic crystals in the Mars rock, arguably the most resilient evidence put forward by the McKay group. (Courtesy Kathie Thomas-Keprta/NASA)

Simon Clemett, in the Building 31 laboratory. The former Zarelab researcher suffered sleepless nights over the vitriolic reaction to the McKay group’s findings. He then joined others working with McKay to push the state of the art in further investigations of several Martian meteorites. (Kathy Sawyer)

Martin Brasier of Oxford speaks during the landmark confrontation with J. William Schopf of UCLA (right) at the NASA astrobiology conference in California, April 9, 2002. In the debate and in a published paper, Brasier challenged Schopf’s 1993 descriptions of the oldest known fossil life on Earth. Like the debate over the Mars rock, this exchange highlighted major blanks in human understanding of the distinguishing characteristics of life. (Kathy Sawyer)

David McKay, in his microscope lab in April 2004, prepares a meteorite sample. More than one hundred metric tons of the world’s most advanced equipment had been brought to bear on the 4.5-billion-year-old Mars rock, and the work continued to reverberate through several fields of study. (Kathy Sawyer)

MEANWHILE, ON MARS...

The Mars Global Surveyor craft, orbiting the red planet in late 2001, captured this image of gullies on a meteor impact crater in the Newton Basin, in Sirenum Terra. The discovery of this and similar features on numerous Martian crater walls startled scientists and triggered lively speculation about the gullies’ origins, including the possibility that they may have been formed by the release of groundwater, or some kind of liquid, onto the Martian surface in geologically recent times. (NASA/JPL/MSSS)

The surface rover Opportunity, in 2004, sighted what looked like blueberries in a muffin, embedded on top of and within an outcropping of rock that was being eroded by windblown sand. The spherical grains contained a mineral that, on Earth, most often forms in water, and scientists concluded that this Martian rock formation had once been soaked with water in liquid form. (NASA/JPL/Cornell/USGS)

. . . AND IN PLACES LIKE MARS

Andrew Steele, foreground, and colleague Hans E. F. Amundsen are among those developing techniques for robotic Mars exploration through fieldwork in Mars-like places on Earth, such as the archipelago of Svalbard, Norway, where hot springs climb up through permafrost. Found here are carbonates similar to those in the controversial Mars rock. (Kjell Ove Storvik/AMASE)

Allan Treiman, an outspoken critic of the McKay group’s interpretations of the Mars rock evidence, at work at Svalbard. Antagonists from all sides of the dispute find common ground in the Mars exploration effort. (Kjell Ove Storvik/AMASE)

CHAPTER THIRTEEN

BINGO

L
ATE ONE DAY
in the last week of October 2000, Kathie Thomas-Keprta was on another expedition into the land of the Lilliputians, riding her electron beam into the deep interior of the Mars rock. She was heading further and further into frontier territory in her drive to solve the riddle that had captured her heart, brain, and soul.

In fact, Thomas-Keprta was about to experience one of those moments when the mind takes a leap that seems to change everything.

For David McKay, her breakthrough on this autumn night would stand out as one of the more satisfying moments in the marathon. With Kathie Thomas-Keprta’s fretful insomniac insight would come, among other things, a sense of renewal.

Those seductive magnetic crystals—particles so small a billion would fit on the head of a pin—had become the most powerful witnesses in the rock. Thomas-Keprta and others on the McKay team regarded them as the closest thing they had to a smoking gun. For years the team had been pushing at the limits of technology as they probed the nuances of the structure. But now, thanks in part to a blunt lecture from a distinguished colleague who was critical of her group’s work, Thomas-Keprta realized she was still not seeing the crystals “naked.” She had
not
deciphered their true nature. She had to go deeper.

While the controversy over the rock churned on, the group had published nothing new since the original 1996 paper. Thomas-Keprta and her lab mates had been working hard, and occasionally described their progress on the magnetic crystals in presentations at meetings. But they had not published.

Now, finally, they had completed and submitted a long, detailed paper for one journal and were finishing up a second, more concise paper for a different publication. They were almost ready to ship that second one out.

But as she went through her paces in the lab, Kathie Thomas-Keprta felt ballooning discomfort about the whole thing. The crystals had her stymied, frustrated. Something about them wasn’t adding up.

It was one thing to go public in the certain knowledge that your results would be attacked when you had results that you
believed
in. It was quite another to publish something that you yourself felt was on shaky ground. You had to be your own worst critic, she reminded herself. She imagined having to defend the work in front of thousands of people. She wouldn’t be able to sleep that night.

Like virtually every aspect of the rock’s deconstruction, the story of the iron-based magnetic crystals—the magnetites—had proved to be unexpectedly complicated. Thomas-Keprta and her coworkers learned, as Bill Schopf and others had, that in order to hunt successfully for the most primitive, ancient forms of life, they needed at least a passing understanding of multiple fields of study—and help from specialists in those fields.

The work of the McKay group and others on this labyrinthine topic would interweave theories of evolution (natural selection), emerging evidence about planetary magnetic fields, the complexities of crystallography, and the nuances of transmission electron microscope techniques, to name just a few.

So they had set about educating themselves on the microbiology and, particularly, on the esoterica of magnet-making bacteria and their environments on Earth. The magnetic crystals in the Mars rock were so mesmerizing precisely because they bore such a striking resemblance to the magnetic structures manufactured by Earth bacteria.

Prominent on their list of go-to specialists was Dennis Bazylinski, a geomicrobiologist at Iowa State University, who had spent years studying the organism known as MV-1, discovered in 1975. It was just one of the several strains of Earth bacteria that somehow grew these iron-based crystal structures inside themselves, giving them an evolutionary advantage over their uncompassed cousins in the survival game. Magnet-making bacteria were devilishly difficult to grow in the laboratory for study, but Bazylinski had developed ways to culture this particular strain.

Thomas-Keprta reviewed the available data. The Earth bacteria, by using these internal magnets to orient themselves relative to Earth’s strong magnetic field, could navigate more efficiently up or down in the water column, to the zone of food and energy where they could best thrive.

The magnetic crystals these organisms grew had special properties, different from those made without benefit of biology. Ordinary nonbiological magnetic crystals tended to be a hodgepodge—formed by precipitating out of water or condensing from vapor. They came in a range of different sizes and, as often as not, interlaced with one another. They tended to be rounded—that is, of a shape that would fit inside a sphere, with corners touching the sphere’s walls—or, as the experts would put it, cubo-octahedral.

By contrast, this unique group of microbes (called magnetotactic) worked from a genetic blueprint. Many of their magnetic crystals tended to be elongated and free of some of the chaotic defects found in the nonbiological ones. In addition, they consisted of highly pure magnetite without the inclusion of impurities common in nonbiologically formed magnetite crystals. The microbes used membrane compartments to wall off a space where they could control the concentrations and interactions of chemicals. They tended to align their magnetic crystal chains head-to-tail, causing the entire chain to behave as a single large magnet rather than a collection of individual small magnets. Microbes, it seemed, tended to grow their magnetic crystals within a crucial size range—just big enough to have a permanent magnetic moment, or directional tendency, but small enough for a number of them to fit into and orient the cell. The result of all this organization was efficiency, more magnetic bang for the buck.

But could counterparts on Mars have evolved in the same way? Had they?

When the McKay group first posed the question in 1996, one of the objections was the lack of any known magnetic field in Martian history. Throughout the space age, researchers had tried without success to detect one like Earth’s, with strong north and south magnetic poles.

So: to what end would a microbe develop a biomagnet on a planet with no magnetic field? The answer arrived fortuitously in 1998, courtesy of the robotic spacecraft Mars Global Surveyor as it studied the red planet from orbit. Sensitive instruments aboard the Surveyor surprised planetary geologists with measurements indicating that Mars had indeed once sported a strong, Earthlike magnetic field—but it had disappeared at least 3.7 billion years ago.

The young Mars had a magnetic field, it seemed, at the same time that it still had vast quantities of liquid water and a carbon dioxide–rich atmosphere—a suitable environment for the rise of microbes. A magnetic field would have protected the Martian surface from the lethal “wind” of charged particles from the sun, in the same way that Earth’s magnetic bubble has continued to shield it—and us.

The magnetic field might have persisted well after the geological cataclysm some 3.6 to 3.9 billion years ago—most likely an asteroid impact—that shocked and cracked the Martian rock formation whose fragment had landed on Earth, pieces of which Thomas-Keprta now studied. That was the impact that, in theory, allowed mineral-rich water to flush through the rock’s fissures and evaporate, leaving behind the carbonate globules—with the enigmatic magnetic crystals strewn in and around them. Now researchers on all sides agreed that the magnetic crystals in the rock, at the very least, contained an important record of the vanished magnetic field of early Mars.

The timing was right: the magnetic field on Mars had apparently been present during the period when, in the McKay team’s hypothesis, Martian microbes might have evolved with little compasses to take advantage of it.

It was a point of ongoing strain, vis-à-vis the critics, that Thomas-Keprta was focusing only on a unique subpopulation of magnetic crystals. All sides of the controversy had agreed that there were varied “populations” of these grains in the Mars rock and that as many as roughly three-quarters had been formed in geological, not biological, processes. Several people objected that Thomas-Keprta focused selectively on just the fraction that fit the biological model.

Wary that this subgroup might be some form of terrestrial contamination, both the McKay group and independent researchers carried out extensive examination and testing designed to assess that possibility. In the view of many scientists, they had fair evidence that this little magnetic clique was Martian.

One reason was that the oxygen of Earth should have changed the iron into a different form from what the researchers found. “If you take some of these magnetites and lay them out on a table,” McKay would say, “they would probably oxidize [into another form] possibly in a matter of minutes but certainly in a matter of a few months. So there’s no way these little magnetites could have been floating around . . . in Antarctica, or washing around in the meltwater, which also has air dissolved in it. . . . These little guys would not remain as tiny magnetites for very long.”

So Thomas-Keprta had pressed on, confident that this particular one-quarter of the magnetic material she was seeing embedded in the carbonate globules, whatever it signified, had been formed on Mars. She was back to the primary point of contention. Were these Martian magnetites made in biological processes?

Opposition viewpoints, as painful as they could be, had continually driven Thomas-Keprta and the others back to do an even more careful, detailed study of the magnetites. They continually felt compelled to try to push their techniques past the state of the art.

“We take our cues from David,” Thomas-Keprta told a visitor to the team’s disheveled War Room, next to McKay’s office. “He is our leader. He’s totally honest, totally trustworthy. We follow David’s cues on this. He tells us if it’s right, if it’s truthful, if it’s honest, you go for it. That’s what you do.”

When she wanted to avoid distraction in order to work on a paper, Thomas-Keprta retreated to her favorite sanctuary, a Starbucks just up the road. She had been doing that a lot lately.

The paper the team had recently submitted was a long and technically detailed description of its work so far on the chemical composition and geometry of the magnetic crystals, based on a study of some six hundred crystals the researchers had separated out of the rock. With Thomas-Keprta as lead author, the paper would be published in the December 2000 issue of
Geochimica et Cosmochimica Acta.
It would generate no more than modest notice in the press but would be warmly welcomed by interested scientists—if only because it finally put the team’s arguments on a factual footing, with firm data all laid out. It gave skeptics some targets to shoot at. And while it would not persuade the staunch opposition, the evidence it presented would be enough to intrigue some of the fence-sitters.

With the first magnetite paper on its way to publication, Thomas-Keprta and her coworkers in the lab were working toward the second, focusing with unprecedented intensity on the geometry of the crystals—possibly the key to resolving the enigma. What was the true shape? Technology that might answer the question had become available only a few years earlier. And the alien microscopic landscape remained devilishly difficult to interpret from a vantage in the macroworld using the fledgling techniques at hand.

Thomas-Keprta knew this. But she had never fully appreciated the nature and extent of the challenge until she received a pointed warning from a colleague on the other side of the argument, veteran meteorite specialist Peter Buseck, a mineralogist from Arizona State University.

Buseck was firmly in the skeptics’ camp on the question of whether the magnetic crystals had been created by Martian microbes. Buseck was also the very same strolling scientist who had inspired Dick Zare to get involved with meteorites that sparkling night several years earlier as they’d walked across the Stanford campus. And that had led eventually to Zare’s and Clemett’s involvement with Mickey, Minnie, and Goofy.

This time, Buseck cautioned Thomas-Keprta that the limitations of the technology might fool her into making a mistake about the crystal shape. After their conversation, she realized that she needed to do considerably more high-resolution imaging of the crystals, and pay a lot more attention to their orientation in three dimensions.

So Thomas-Keprta went on a new hunt—a hunt for “the perfect crystal,” the one that could best help her make a strong case about the three-dimensional crystal structure. She began a survey of the magnetic crystals as they sat inside the rock samples—still embedded in the carbonate moons. Attempting to look at them as they sat in their carbonaceous matrix, rather than dissolving them out of the carbonates for separate mounting, would make the detailed observations much more difficult and time-consuming. But she felt it was better to look at them this way because the nature of their surroundings—their context—made a difference in the arguments about whether they had formed biologically or nonbiologically.

She and her coworkers spent three months taking hundreds of thin samples from the rock in their hunt for this ideal crystal. Finally, the rock yielded up a beautiful specimen that fit the bill. It was in just the right orientation. It could be tilted through ninety degrees, so the observer could look down the top of the crystal and down the side. And yet it was still completely embedded in its carbonate surround.

Thomas-Keprta nicknamed the wonder particle Bingo.

With the power of her cathedral-tower microscope, its beam of electrons taking the place of light, an observer could actually manage to see the infinitesimal object—a bit of iron oxide, something like a speck of rust, about a millionth of an inch in diameter. But the mighty transmission electron microscope could show only two dimensions, revealing the object essentially as a dim silhouette. It was, Thomas-Keprta thought, like standing in bright sunlight looking into shadow. The task, again, was to translate the two-dimensional information into a three-dimensional shape—to distinguish a flat face from a tapered edge, for example, when the two looked the same in profile. She and her coworkers would aim the high-powered electron beam at Bingo and tilt the sample painstakingly by hand through a sequence of dozens of angles in a carefully chosen and executed pattern.