The Rock From Mars (9 page)

With the two Viking missions of the 1970s came “a giant and abrupt escalation in Mars exploration.” Among other things, the Viking landers conducted the first probes in search of organics—signs of possible biology—in the Martian surface soil. Almost everybody concluded that the answer, at least for that time and in those two spots three thousand miles (five thousand kilometers) apart, was no. They’d found no organic molecules and unexpectedly sterile soil. If Earth had a mountain three times as high as Mount Everest, its peak rising 100,000 feet into the stratosphere, exposed to ozone and ultraviolet radiation, conditions there would be Mars-like.

Still, the two craft had landed in flat desert terrain, where they were more likely to survive the touchdown but arguably less likely to find organic material. And the sensitivity of the instruments was far less than what could be applied in current state-of-the-art Earth labs.

The news was agonizing for some, in part because the evidence was so tantalizing. A few scientists would insist that Viking said something closer to
maybe.
Indisputably, the experience provided an early lesson in the difficulties of distinguishing signs of alien life-forms from unpredictable chemical reactions on an alien world.

Still, accumulating evidence indicated that, billions of years earlier, the young Mars had been even more Earth-like, with flowing waters and a warmer climate. In the 1990s, NASA would adopt a single organizing principle for its Mars explorations: follow the water. This would be the overarching theme of the struggle to understand the planet.

And now, as the United States readied a new wave of Mars-bound robots, an important new clue presented itself courtesy of Duck Mittlefehldt.

In October 1993, Mittlefehldt revealed the discovery of a new Martian meteorite.

The rock Robbie Score had plucked from the ice almost nine years earlier was hailed as extraordinary even in the exclusive coterie of SNCs. The news spread rapidly by word of mouth in Building 31. Score, working in the meteorite archives, was thrilled when a coworker mentioned it—but not all that surprised. She had always known that the rock was weird.

Down on the first floor, David McKay’s ears perked up when he detected the hallway buzz about the new find. While still working on his lunar soils, he had also branched out into studies of meteorites and cosmic dust. In fact, he was for the first time getting money from a division of NASA devoted to studying the possibility of extraterrestrial life. McKay had won the grant for his proposal to analyze cosmic dust for carbon (a building block of life). He and a coworker, Kathie Thomas, came up with results that showed a much higher abundance of the stuff than anyone had expected.

McKay volunteered to join a little consortium Duck Mittlefehldt had formed to share his samples of the intriguing new Mars rock.

As more and more people got their hands on bits of that rock in the months that followed, they learned how special it really was.

This was the first rock ever studied that appeared to have formed
beneath
the Martian surface, probably on the floor of a magma chamber. Investigators therefore anticipated a rich vein of new information about the geological processes that had helped shape the red planet. And the rock’s unusually high concentration of carbon compounds, possibly from molten subsurface volcanic flows, provided what Mittlefehldt considered “probably the first convincing case for [a tangible storehouse] of primordial carbon inside Mars.” Not that the thought of Martian biology was on his mind at this point, but still—carbon was the congenial element that provided the essential framework for all known life. Requests for pieces of the rock poured in, dozens of scientists around the world began to scrutinize it, the march of revelation was under way, and the “batons” were flying like mad.

The next stunner was the rock’s age.

Geologists in Germany used a tried-and-tested geological clock—the processes of radioactive decay—to show that the Martian material in question had crystallized 4.5 billion years ago.

The rock had hardened out of a molten volcanic flow as it cooled down on an infant Mars still forming in the wan light of the newborn sun. Almost as old as the solar system, the rock was more than three times the age of the next-oldest known Mars meteorite. And the oldest native Earth rocks ever examined dated back no more than 3.8 billion years.

The rock from Mars, in short, was the oldest known from any planet. It was rivaled in age only by the meteorites that came from asteroids. Like a message in a bottle, the pilgrim stone carried an unprecedented record of eons of Martian geological history.

Here was the Ur-rock of planetary memory.

Excited investigators soon showed that the rock had started its road trip some 16 million years earlier as an unguided ballistic missile—blasted off Mars by an incoming asteroid or comet. They did this by measuring the effects of the high-energy cosmic rays that had bombarded it as it traveled. They estimated how long the rock had been imprisoned in the Antarctic ice sheet (13,000 years) by measuring the radioactive decay of products of that long pounding in space.

Some researchers studied impact craters on Mars with the goal of figuring out where the rock had been situated at the time of the jolt that liberated it. The theory was that, given the rock’s age, its home neighborhood was in the heavily cratered highlands of the southern hemisphere, the most ancient terrain on Mars. An impact scar in the Sinus Sabaeus region had the right age and characteristics.

The record that most fascinated Duck Mittlefehldt and others had to do with a major impact that had traumatized the rock, possibly within a billion years after it had first cooled and hardened. At that time, the rock had been severely shocked and had cracked, presumably when an asteroid or comet plowed into the surface nearby. The resulting fissures and crushed places allowed the ephemeral chemistries of the changing Martian environment to infiltrate and leave their signs.

The rock seemed to offer clues, in other words, from a time not much less than 4 billion years ago when the worst barrages of violent collisions that had wracked the early, rubble-filled solar system had abated and the climate on Mars was relatively warm, with liquid water flowing or standing. The conditions on Mars in that season might not have been so terribly different from those on the toddling Earth of the same period, where primitive life might already have formed.

Accordingly, in late 1993, those who liked to delve into the histories of worlds delighted that here, in this single lump, they had found a key that could help them decipher Mars’s most deeply buried secrets. And in time it would become arguably the most intently studied of all known meteorites. What they didn’t suspect was how much the rock would reveal about Earthlings. While they were looking into the rock, it would be looking back into them.

Mittlefehldt and others focused on the rock’s unusual and puzzling abundance of carbon compounds, especially its carbonates. They made chemical maps showing that the compounds were quite complicated and varied in composition and, as far as Mittlefehldt could tell, distributed all through the rock. But many looked distorted, ruined. The ones with a certain rounded shape, some big enough to be visible to the naked eye, seemed to have been deposited in high concentrations along fractures in the rock. He visited the rock in its permanent quarters in the meteorite lab (to look at “raw” pieces not yet prepared for analysis) and noted that whenever he saw a face that was one side of a fracture, it was loaded with those rounded carbonate globs.

The rock detectives knew that carbonates, such as limestone (chalk), formed in water and were most commonly a by-product of sea-dwelling
organisms
(though they could also be formed in purely chemical, nonbiological processes). Carbonates were found in beds of fossils laid down in the slow accumulation of shells from defunct sea life. Oceans? Animals? What were these carbonates doing inside a very old
volcanic
rock that, moreover, came from Mars?

Mittlefehldt knew just who to ask.

Like several others in Building 31, Mittlefehldt had developed an admiration for a young man named Chris Romanek. Even though he was barely out of school, Romanek, thirty-five, had gained a reputation as an impressively sophisticated specialist in carbonates.

Late one evening in November 1993, Duck Mittlefehldt appeared in Romanek’s doorway. “Hey, Chris, you want to see some really neat pictures of a meteorite I’m working on?”

“Sure,” Romanek answered, looking up from his work. He walked across the hall with Mittlefehldt to the other lab. There, on the little CRT screen on Mittlefehldt’s electron microprobe, Romanek stared at the images of tiny circular globs—a firmament of orangey rosettes arrayed along the rock’s fissured surfaces, flecks big enough to be visible to the naked eye but only about the diameter of a coarse human hair.

“That’s fascinating.” Romanek said. “What is that?”

“Carbonates.”

“Whoa, carbonates?!”

Mittlefehldt explained that this was a sample from a Martian meteorite. Romanek asked which one, unaware that any of them had such a rich lode of his favorite stuff. Mittlefehldt told him it was a new one that he, the Duck, had just unveiled. (The intriguing carbonate globules would be variously referred to by researchers as “rosettes,” “orangettes,” “orange spheroids,” “rounded zoned blebs,” “disk-shaped concretions,” and “spheroidal aggregates,” among other things.)

“Well, Duck, you’ve got to get a piece of that for me.” Romanek felt confident he would be able to pry into this mystery and find out how the carbonates had gotten in there.

Research on the strange rock might have simmered along indefinitely were it not for young Romanek. But he had grabbed the baton, and he would carry it in a direction that no one expected.

Slender, athletic (a runner), newly equipped with a Ph.D. from Texas A&M, Romanek was a “low-temperature geochemist.” (The term wasn’t a hip reference to his personality or his metabolism; it delineated the particular focus of his studies.) When he’d been in high school in the foothills of South Carolina, an alert teacher had recognized the young man’s affinity for science and helped him set his course. Eventually, Romanek had focused on what happens in the oceans of water that, so far, were not known to exist anywhere in the universe except Earth.

In graduate school, Romanek concentrated on clams that live in the middle of the Pacific. He studied the carbonate shells in an effort to understand how these particular bivalves grew their shells and what kind of information was locked inside them. He planned to use that work to study bivalve shells of fossils from extinct organisms, to see if he could understand the biology of some creature that no longer existed.

At a certain point, Romanek realized that he really didn’t know much about the “tool” he was using, courtesy of the clam. So he went to Texas A&M to work on his Ph.D., and, instead of having a clam grow a shell for him, he grew his own crop of the common
calcium
carbonates that form on Earth—the cements that hold certain rocks and sandstones together, the components of seashells. He watched carbonates precipitate directly out of a lab solution so that he could understand what was happening to their atoms (the isotopic ratios) as the substance moved from the liquid to the solid phase. That helped him understand which types of information you could extract from a carbonate in the natural environment, whether it had been formed by living things or in a nonbiological natural process such as in a hot spring deposit.

What captivated his mind in all this was the realization that when you looked at the natural world around you, objects had stories to tell about how they had formed and about the influences that had altered them. The shells formed something like tree rings. An organism was born. It grew a shell through its life, and it died. Where others saw a plain old shell, Romanek saw a tape recorder, and it was recording everything that shell experienced in its life.

He found it remarkable that when you collected a living organism, a living bivalve just out of the ocean, you could take the shell and analyze it and figure out, well, this organism is five years old and has lived in this area for a certain fraction of that time. You could also take a shell from a deposit that was 300 million years old and learn something about its daily life 300 million years ago. The idea blew his mind.

When he arrived at the NASA space center in Houston, in 1991, on a postdoctoral fellowship, Romanek had never met a meteorite. His main assignment was to devise a new way to sample rocks and minerals in order to study them with pinpoint precision.

His goal was to shoot a very tight laser beam—perhaps a few thousandths of the diameter of a fine hair—onto a rock surface and measure the properties of its atoms (its isotopic ratios) in order to learn at what temperatures they formed, and in what kinds of processes. An isotope of an element—say, carbon—represents a variation in its atomic recipe that matters only under certain circumstances. The heavier isotope of a Toyota, for example, would be the same model of car but with a permanent extra load—the equivalent of extra neutrons—in the trunk. The car, like the isotope, would have all the same functional properties but with more mass.

At first Romanek blasted away at earth rocks, since they were plentiful and he didn’t want to waste good meteorites as he was still working out the glitches. His original intent had been to use the new technique to look at very old Earth rocks, to study their carbonate minerals for signs of biological activity.

But by the time Duck Mittlefehldt showed him the carbonates in the Mars rock, Romanek had not only gotten the new technique working pretty well; he had developed an appreciation—even enthusiasm—for space rocks.

Romanek’s mentor at NASA was the geochemist Everett Gibson. One of the old Apollo hands, he was now a senior scientist in the isotope lab. When Gibson and Romanek had first talked a couple of years earlier, Romanek had said, “You know, I’d like to come down. I know that you got this laser, I know you’ve got this wonderful isotope ratio instrument, and I’d like to come down and try to interface these things.” Gibson had said, “Yeah, Chris, well, maybe you can work on some Martian meteorites.”