The Rock From Mars (37 page)

Jerry Lipps, the emcee, thanked Schopf “for a rousing good introduction of the two hypotheses we are dealing with this afternoon.” He welcomed Martin Brasier, who with seven colleagues was “questioning the evidence for earth’s oldest fossils.”

Brasier took to the stage looking something like Sir Laurence Olivier as King Lear, a patriarch with a mane of white hair on a large head and a tuft of white on his chin. His delivery was as understated as Schopf’s had been dynamic, but Brasier had the advantage of also sounding like Olivier. While Schopf had referred to him as “Dr. Brasier,” Brasier called Schopf “Bill.”

“Well, thank you, Bill,” Brasier began softly, as he positioned his material on the projection machine and jabbed his rhetorical rapier in Schopf’s direction. “A truly hydrothermal performance. . . . More heat than light, perhaps.” Laughter rippled through the audience.

“What we want to do in this group, which is based in Oxford, is to question very deeply all those mantras, those understandings we’ve had about the nature of the early fossil record. And it’s as much a shock to us as it might be to Bill about the conclusions that we’ve had to come to. It was no easy decision, but each time we inquired deeper, we found more that was unsettling about the existing paradigm. Of course there is always a lot of fighting when a paradigm has to shift. . . .

“We have until now all assumed that the reports of microfossils and stromatolites from rocks about 3.5 billion years old represent the beginning of the fossil record,” Brasier said. This assumption also dated the beginning of the process—the metabolic activities of Schopf’s microorganisms—that gave rise to Earth’s oxygen atmosphere.

As Schopf had acknowledged in his book, this was a “puzzling scenario” that some scientists privately wished he had been wrong about. It meant that the basics of the world’s ecosystem had evolved with dazzling rapidity.

“And of course,” Brasier continued, “we have noticed over the last few years that, in some people’s view, there’s a major mismatch between the appearance of such complex fossils and the emergence of an oxygenic atmosphere” perhaps millions of years later, although the timing was uncertain. “And we’ve heard other reasons too . . . as to why cyanobacteria might not be expected so early. So we have to be very careful with those kinds of arguments.”

Brasier had gone to Schopf’s material “with great excitement,” he said, “because I did my doctoral research in evaporitic lagoons around the Caribbean, and had worked on microbes and microfossils all my life. In fact, the reason I wanted to get images of these microfossils was to include them in the next edition of my textbook on microfossils, and I thought it would be great to have a look and get some good images using new techniques. And really we think that the change in view has come about by all the new techniques that we can now apply to these particular rocks: geochemical techniques, image analysis techniques and so on.”

He showed a sample of the rock “fabric” that contained Schopf’s microfossil-like features. “I was aghast, I must admit, to see just how complex and brecciated [rubbly, coarse, sharp-cornered] it was,” he said. He described recent findings on the complex geography of the rock formation from which Schopf had taken the samples, where one kind of material transected another, and some layers had quite different histories of heating from others.

“We were intrigued to discover a range of minerals in this which turned out to be very suggestive of a hydrothermal setting,” Brasier said. “. . . The more we did, the more consistent it seemed to be with a hydrothermal setting and the less consistent with any sort of stratiform wave-washed beach or river.”

Now he raised a question about stromatolites—those geological formations that had fascinated Schopf from his early days, in China and elsewhere, with their artistic layering constructed by a zoo of microbial communities dominated by cyanobacteria.

“What is a stromatolite?” Brasier asked. “One of the things we are doing at Oxford at the moment is to explore the real meaning of the word
stromatolite.
Here is a sample we’ve been working on.” He showed a slide of varying colors in curving layers. “It was originally in the collection of Sir George Taylor, curator of Kew Gardens, and is a beautifully digitate structure, branching, and so on.”

Then he sprang his punch line.

“But we know this is actually made out of
paint.
It turns out to have been made probably in a car works. You can make out different colors here. There’s pink and green and pale blue. Many of you will perhaps recognize cars of the late 1950s, early 1960s, in that color scheme.”

Noting that his team had been conducting a series of experiments at Oxford on how the stromatolite structure develops, his voice rose with indignation as he added, “You can’t just use stromatolite as a biogenic indicator.”

As Brasier spoke, Schopf stood nearby, onstage, with his hands clasped behind his back, leaning so far forward to listen that he seemed on the verge of tipping over.

Brasier addressed the distribution of the microfossils within the material itself. He showed slides of the famous Gunflint Formation on the border between Minnesota and Ontario (the subject of the young Schopf’s Oberlin honors thesis), with its “microbial mucilaginous dark layers here, and then you can see the various filamentous structures forming a distinct layer and then intertwining one around the other. Usually the structure’s of about the same length and not showing complex organization.”

Next, for contrast, Brasier showed a slide of one structure from the microfossil-containing fragment of Schopf’s history-making Australian Apex chert. “This is a thing that is ‘arrowed’ as a microfossil [in the published paper], and these are the sorts of structures that float around it. It’s quite varying in length, it’s a rather ugly-looking little structure, and it contains various little chaotic, information-rich organic blobs and wisps throughout the matrix, and that is absolutely typical of the appearance of the Apex chert organic matter.”

Then he showed images from the new Auto-Montage technique he had used to study the samples, revealing the new details in the alleged microfossils. A single threadlike structure in the Schopf paper viewed in this way became something else.

“We were surprised,” he said, “to find that a great number of the structures, many more than just three or four, were more complex than were present in the descriptions, and in the illustrations” in Schopf’s published papers. “In this particular one, it balloons out here . . . into a large bulbous mass which then turns this right angle. And this structure is continuous.” Brasier took issue with the argument Schopf had just made—about the folding over, like an AIDS ribbon: “There’s no illusion here, in which one is montaging one piece on top of another.”

Brasier put up a topographic map that showed, in effect, the
altitude
of the features. Where Schopf had seen cyanobacteria, or something cyanobacteria-like, he said, “we found it was much more complex and branched than is ‘normal’ for cyanobacteria of that age”—i.e., the type alluded to by Schopf.

Brasier and Schopf were diametrically opposed in their arguments about the shapes of the fossil structures. Were they actually branched like a
Y,
as Brasier insisted, or just folded like the AIDS ribbon, as Schopf argued? For his part, Brasier was incredulous that Schopf, in his papers, had “never described folding,” much less branching, in the fossil-like shapes. Schopf “ignored the folding,” Brasier had concluded. But had Schopf missed it or simply failed to describe it?

Almost three months later, a former graduate student of Schopf’s would voice her own reservations about Schopf’s representations in his original papers. Bonnie Packer, who had first spotted signs of biology in Schopf’s Apex chert samples, would tell the journal
Nature
that Schopf had indeed been highly selective with the evidence as he’d presented it from 1987 into the early 1990s. Schopf, she would say, had withheld from publication images of the supposed cyanobacteria that showed branching, and her attempts to challenge Schopf had met with stubborn resistance. “There wasn’t a bloody thing I could do,” she told the journal. To back up her account, she provided pages from her lab notes and described photos with Schopf’s handwriting on them. Schopf would respond at first that Packer had never revealed the branched shapes to him, but he would later amend that to say that his memory on the topic was sketchy.

Brasier, as he looked out at the rapt crowd, discussed the process by which crystals form and showed what that process could do to organic matter to make it look like microfossils. “You get a spherical structure, with a kind of spherical symmetry to it, and as you move away you get a kind of radial symmetry or a bilateral symmetry, and then as the material gets scarce the matter self-organizes into information-rich filaments exactly in the way that complexity theory would predict, and these take up the appearance of microfossils.” His group had found a lot of this, he said.

“When we looked at the whole spectrum—and of course we have imaged thousands of structures, and I have spent thousands of hours looking at this material,” Brasier went on, “we went through the material imaging absolutely everything and not just hunting for things that looked like fossils”—an approach he pointedly contrasted with that of Schopf—“and we found structures which . . . clearly had branching that had never been discussed [by Schopf or anyone else in published papers], such as . . . the so-called AIDS ribbon–type structures. . . . And we found others which were so chaotic in their organization, so information rich”—he pointed to the images on the screen and revealed what his group had nicknamed the confused shapes—“like this one we call the ‘little ballerina,’ this one is the ‘Loch Ness monster,’ this one is the ‘wrong trousers’—these are so complex, or so large . . . that you really have to scratch your head and ask, maybe there’s some terrible mistake?”

He discussed the graphite and the particular way the quartz structure formed, which might explain other suggestive features—segmented shapes—without biology. “I don’t think any of us would be confident in staking our reputations [on these features] as microfossils.”

Brasier moved on to his last point: the light-carbon isotopes that seemed to imply living organisms. Noting that his group had pondered whether some kind of nonbiological synthesis could have produced the signature, he said, “We don’t believe the tools are yet at hand for distinguishing the one from the other.” Brasier considered the current state of scientific knowledge so scanty that it seemed naive to think anyone could safely rely on isotopic signature as a sign of life. Carbonaceous matter and light-carbon isotopes were also abundant in comets and meteorites, after all, but in those cases they were certainly not believed to be signs of biology.

Brasier summed up: “So, the position we take, which is different from Bill’s, is what I call the Oxford audit on astrobiology, and it’s tentative.” Brasier’s default position was that no structures should be deemed to be biological in origin—whether from Earth, Mars, or elsewhere—until possibilities for their nonbiological origin had been exhausted.

Developing ways to rule out the nonbiological option “is an agenda for future work,” he said. “It really says that we must explore all the [nonbiological] look-alikes in these various kinds of marker, before we can confirm the biogenicity of structures. Otherwise, the material you bring back from Mars, or the material we collect from early Earth, will be subject to long and futile debate.”

After recapping his group’s conclusions, he added, “We think our hypothesis fits better with a hydrothermal cradle for life . . . which Bill has now acknowledged, and it also opens the possibility that the geological record will contain much more of the evolutionary history of life than previously thought.

“So, astrobiologists,
go to it.
Thank you very much.”

Lipps, the emcee, opened the floor for questions. Scientists and journalists were lined up at microphones placed in the aisles.

One asked whether certain parts of the sample material might represent precursors to life, if not life itself. Another raised a question about the stromatolites. There were exchanges about how much had been published on the topic of whether some of these features could be created without biology—and about how certain anybody could be either way.

Schopf, still standing away from the podium, off to Brasier’s side, moved closer and leaned forward to hear better.

Brasier repeated his call for better criteria to discriminate between biological and nonbiological processes. He raised his voice: “When we’re thinking about the early earth, we have to be thinking about how life originated.” Scientists had been accumulating evidence that the change had occurred along a chemical continuum. “We must therefore be thinking of a
spectrum
between abiogenic generation of organic matter and biogenic generation,” he said. “It seems to me absurd to close the door on some of those processes before the discussion is begun.”

Andrew Steele stepped to the microphone. His comments launched a fresh punch-counterpunch between Schopf and Brasier.

“Couple of points,” Steele began. “On the carbon isotope signature work, we [in the Brasier group] are trying to say that it could be a biogenic or nonbiogenic origin. It could be a hydrothermal vent community. One thing that’s important for me as a microbiologist is I’m not hearing the word
cyanobacteria
at 3.5 billion years anymore. That’s extremely important, and that’s the point I wanted to make more than anything. . . . No cyanobacteria.”

In other words, he was noting that in the weeks since the Brasier paper had appeared, Schopf had backed off his original claim as to the identity of the world’s oldest known fossil life-form.

Schopf stepped up to the podium. “If I understood what you said, you are not hearing the word
cyanobacteria,
is that correct?”

“That’s correct.”

“Okay, let me explain,” Schopf began, “because a whole lot of you are not professional paleontologists, paleobiologists, who have to deal with this problem. Put yourself back ten years ago and imagine that you have found a feathered dinosaur. Well, there
are
such things. Okay? It has the anatomy of a dinosaur, but it has feathers on it. But this is the first one that’s been found. There are quite a bunch that now have been found. But ten years ago this would have been a great find. What would you do? You would say, well, it might be a reptile, might be a dinosaur, or it might be a bird.” He used the term
incertae sedis
(of doubtful position), the Latin term applied when more data is needed in order to place a find in its rightful place in the taxonomic scheme of living things. “What that means is I don’t know for sure whether it is a bird or a dinosaur. Well, that’s exactly what I did. I compared these organisms with modern cyanobacteria and fossil bacteria. . . . I looked at some two thousand living species and strains of bacteria and cyanobacteria so I could make a good distinction. I came up with the conclusion that the things—I call some of them ‘cyanobacterium-like,’ and other ones I called ‘bacterium-like.’ . . . My best judgment is, what I could say without misleading anybody, is that these are prokaryotes [organisms in which the genetic material is not enclosed in a cell nucleus]; I believe they are members of the bacterial domain, . . . but I can’t tell you for sure whether they are cyanobacteria, or bacteria, or some now-extinct group. And I did that even though one of my distinguished colleagues urged me to name them, like, proterazoic cyanobacteria. I resisted that. I did that because I thought it would be fairer to the scientific community.”