The Rock From Mars (38 page)

Schopf had begun to enunciate emphatically again, his hands gesturing more widely. “I did not want to prejudice people. So I have been personally very careful about saying cyanobacterium-like, bacterium-like, but
by golly, folks have forGOT-ten . . . to . . . read . . . the . . . literature!
”

Brasier came to the podium as Schopf stepped back. Brasier said quietly, “What we do is more or less paraphrase exactly the sentences that were in the various [Schopf] papers. We were most careful to do that. And we say things like ‘compared with,’ not actually ‘placed within.’ So there’s a slight difference of opinion there.

“What I would like to ask Bill, uh, then, is,” Brasier said, and he reeled off a series of Latin names Schopf had given his organisms, “and these various other structures, when we imaged them, we found they had complex and perplexing structures about them which were not shown either in the figures [that Schopf published] or were not even referred to in the taxonomic descriptions. It would seem to me an essential part of taxonomic description to closely proscribe the nature of the structure that you’re looking at and to help us scientists understand how much selection of information is going on and how—” Brasier interrupted himself abruptly and stepped back as Schopf moved quickly to the podium.

“Well, I appreciate the chance to answer that question,” Schopf said, “because it is of some interest. It is of interest to me.” He gripped the podium with his left hand, while the right swept air. “As you know very well, in the first instance, anytime one, uh, publishes a paper, you have a lim—” He cut himself off to say, “especially in
Science,
where this was published; this should have been in the
Journal of Paleontology,
Andy Knoll was right, I should have done that, but I was following Elso Barghoorn, and I thought maybe that he’d made the right decision. Anyway, I made the wrong decision, should have put it in a place where I had more space [to include more information]. But you’re always constrained that way. The fact is, the rule is, that
you show in-for-ma-tion-containing
photographs and, in your taxonomic descriptions and all that. If, for example, Dr. Brasier had been correct—he’s demonstrably wrong because I showed it to you on the slide—but if he had been correct that those . . .” Sounds of protest came from the audience. Schopf retorted, “No, I did. And if these things were in fact branched it would have been wrong if I had not put that in the paper. But the fact is they’re not branched, they’re curled back under themselves. I wasn’t using Auto-Montage confocal microscopy. And thank goodness, because I could see the optical planes clearly and that’s what I published.

“And let me say one other thing. Imagine that you are put in the position where you have found a new genus, or a new species of fossil wood. That’s a good analogy because these fossils are preserved by petrifaction. Some folks get excited that the organic matter is, quote, wrapped around quartz [as Brasier had suggested in this case]. Well, of course it is. There’s quartz inside the cells, quartz outside the cells, that’s what petrifaction, permineralization, is all about.

“So imagine you have a petrified log. Now, it’s not at all uncommon for a part of such logs to be poorly preserved. They’ve been eaten by fungi, they’re decayed, and so forth. And you’re going to name this new, petrified log. What you do is study the cells in it. You’d look at each tissue type, you’d show the variability in those tissue types, and so forth, but you would not waste a whole lot of space showing where it had been degraded by fungi, where it had fallen apart. And that’s exactly what is done. It seems to me that those of us who’ve had a lot of experience looking at Precambrian microbial communities and looking at the taxonomy of modern microbial communities know very well that you have some living forms, you have some that are recently dead, you have some that are degraded, partially, you have some that are essentially bits and pieces of stuff,” and other material, he said, that contains no useful “information.”

A woman from Arizona State University asked, “In the big picture, if Dr. Schopf’s fossils are disproven, what implications does that have for the atmosphere of Earth and the evolution of Earth’s atmosphere through geologic time?”

Brasier replied that before this conference he had consulted a well-known expert on the topic, paleobiologist Hans Hoffman. “He looked at the material and he said that he would not have described many of these structures as biogenic, that he felt that those that were more suggestive might be ‘dubio-fossils.’ But what I was really interested in was how far back would we have to go to find an assemblage of comparable complexity, or I should say diversity. [The expert] said more or less what my thought was, that the foundation on which we feel we can all build, without controversy, is going to be the Gunflint chert,” dated at 1.9 billion years old.

“Now, if that is true,” Brasier continued, “that will be an astonishing stirring of the paleontological nest—from 3.5 to 1.9 [billion years]. I honestly believe that is
not
going to be the case. There are various indications—biomarkers, always questionable, stromatolites, always a little suspect, possible sheaths, always a bit vague—that things might start to come out of the mists about 3 to 2.7 [billion years ago]. Now people will debate here when the atmosphere actually became oxygenic. And I don’t want to get involved in that. But there are others here . . . who feel that oxygenation took place relatively late, 2.3 [billion years ago] or afterwards. And that would be consistent with a later appearance of the cyanobacteria. . . .

“So whatever you do, it causes us to have tremendous pause, and thought, about that interval, between 3.5 and 2.5 in particular. I think we’ve got to look very carefully and intensely during the next two years to see if we can’t pull out what the real scenario is.”

Schopf, who had been standing nearby, listening with his head bowed, took the podium.

“I think that’s a very interesting question,” Schopf began slowly. “I think it’s also important, probably, to make a distinction between facts and models. And maybe between what we see and what we wish to see, what we’d like the answer to be.

“Dr. Brasier is a good deal bolder than am I,” he noted, triggering a round of laughter in the audience; Schopf paused, hiked his eyebrows, and grinned mischievously. “. . . I mean, I did show you, or at least mention the work of”—here he reeled off the names of prominent scientists in the field—“and that’s the tip of the iceberg. And all of these people, it seems to me, are really quite experienced, and it would seem to me it’s unlikely that they are wrong.

“But with regards to your specific question regarding, let’s say, the Apex fossils do not exist. I don’t think it makes much difference at
all.
The fact is—unless one wants to throw out about five hundred isotopic analyses, and unless one wants to say, even though they’re consistent with everything else, for some reason we don’t like them, and unless a person wants to throw out roughly forty Archaean stromatolitic occurrences with hundreds of stromatolites, including one at 3.49 [billion years ago] in the Dresser Formation . . . that goes over tens of square kilometers, unless you want to throw all that out, what the fossil record is telling us is that there was life on this planet.

“And we still have to fight the thing out, ferret out the evidence, to tell us whether it was oxygen-producing or not oxygen-producing. That’s still a very important question. And what sorts of organisms they were. . . . We need more data. I must say in closing here that it seems to me that there are two things: Having Dr. Brasier and his group become interested in this problem is a great boon to us all. We need folks asking questions about the early history of the Earth, and we’ll figure out what the answer is. That’s the way science operates. If the data are good, they will stand up.”

“And I’ll say one other thing. I mean this seriously and I mean it respectfully.” Here, Schopf cataloged, again, what he saw as the Brasier group’s concessions. “I personally am very thankful that Dr. Brasier and his colleagues did the work that they did, because you see they started out saying there was no detectable organic matter in the rock, and now have come back and said yes, there is. . . .

“All these things indicate biogenicity, so the evidence is far
stronger
thanks to their questioning. And since they set out to
debunk
this, it makes it even more strong. ’Cause if someone’s out to show you that you’re wrong, and they come around to your point of view, it means, gosh, you might have a chance of being right.”

The crowd was laughing again. Brasier had taken a position just behind Schopf and had been shaking his head emphatically during the last few comments. Brasier moved up to the podium.

“I’ll just say that we didn’t set out to debunk Bill Schopf’s hypothesis at all,” Brasier said, smiling. “It was a hypothesis which developed as we looked further, and the whole thing about science is that you keep looking and you gradually modify your approximation to the truth. We will never, probably, know the truth about all these things. All we can do is get approximations. . . .

“Finally I would say that I would applaud Bill for having produced a hypothesis which . . . is eminently testable and falsifiable. It was a bold hypothesis. We’ve attempted to falsify it. The last thing I would say is that Bill Schopf—and he doesn’t know this—was the man whose lecture I went to back in 1973 or 1974 that determined me that I wanted to be a Precambrian/Cambrian paleobiologist. So—compliments to you.” He nodded and bowed slightly in Schopf’s direction.

A
U.S. News & World Report
writer took the microphone to call the whole conversation a delight for reporters, saying “It’s nice to see people with their heels well dug in.” He asked Brasier if he had conceded there was “a plausible biotic scenario to explain these structures?”

Brasier answered no, drawing a distinction between the organics and the fossil-like structures. “Not to explain the structures. I don’t think anybody who has spent more than a few hours looking at the range of materials that we have, and you can see this when we rotate these structures in three dimensions, would feel that you could have any confidence in these as actual morphological microfossils. I don’t dispute for a moment that a biogenic interpretation for the organic matter is open. . . .”

Turning to Schopf, the journalist asked, “You’re now an agnostic on whether these things produced oxygen?”

Schopf answered, “Agnostic as used in a theological sense. . . . Let me say that the data that are available at the present time are consistent either with oxygen-producing photosynthesis” or with other kinds of microorganisms.

As the crowd started to thin, a
Washington Post
reporter asked Schopf to compare his current position with that of David McKay in 1996, when Schopf was more or less “on the other side of the debate in terms of the evidence and its strength.”

“Heavens to Betsy!” Schopf answered. “Heavens to Betsy, no! I made the statement at the news conference—it’s very kind of you to remember I was even there—when the Martian objects and data were first revealed. I said at the time, I quoted Carl Sagan, and said, look, this is an extraordinary claim. . . . After all, we have no evidence of life on Mars, we have no evidence of fossils on Mars, we have no evidence of organic matter
—kerogen—
on Mars, we have no evidence of the isotopic composition of Martian material. This was a one-of-a-kind deal.

“Now I ask you to contrast that with what I’m talking about [in the terrestrial evidence]. I have just listed off the names of fifteen or sixteen people who have contributed to a biogenic interpretation between 3.3 [billion years ago] and 3.5 [billion years ago]. We have fifteen hundred carbon isotopic analyses on the Precambrian of this planet. We have seven hundred petrified microbial communities just like the one we’re discussing. We have thousands of stromatolites. We know what sort of organisms ought to be there, and these are not otherworldly. They’re the right size, the right shape, the right form, and the whole business. So this isn’t extraordinary at all. It simply is an extension of knowledge at one time. Now it fits into that knowledge and fits in with what we knew before.”

The face-off had lived up to expectations. Two intellectual virtuosos, quick, articulate, and worthy adversaries, had gone for each other’s eyes. There was the tectonic sense of pillars swaying, edifices teetering, inky pigments dissolving in the pages of textbooks. The two men had touched on fundamental gears and levers of the scientific process, and on great burning questions of the day. They had left devastation and disarray in their wake, and this was much appreciated by their audience.

A few weeks later the journal
Nature
would report in its June issue, “Most judges gave a clear points victory to Brasier,” while Schopf “had won few converts to his cause.” A report in
Science
was kinder to Schopf.

The questions about the nature of Earth’s oldest fossil life, it seemed, would remain in flux for the foreseeable future, in a kind of paradoxical unity with the even more vexed question of whether biology had flowered on the young Mars.

Andrew Steele greatly enjoyed Schopf’s acknowledgment that his specimens were not oxygen-producing cyanobacteria. Others agreed, noting that if, as Schopf conceded, the source of the fossils was a hydrothermal vent deep beneath an ancient sea, there would not have been enough light for the organisms to use photosynthesis.

For many scientists, the notion of oxygen-producing bacteria at such an early time had been the crucial element of Schopf’s claims, and the most difficult to explain. Without that, they would lose interest in the issue of whether those features were fossils or not.

Just as many scientists had lost interest in McKay’s claims.

Andrew Steele would come to decide that all three men—Schopf, Brasier, and McKay—had pushed their interpretation of the evidence beyond the point where they could be definitively persuasive. But he believed, like many others, that pushing the envelope pricked and stung and stimulated the broader population of interested scientists to new learning. In Steele’s view, however, David McKay and Martin Brasier had pressed their case for the “right reasons,” and Bill Schopf apparently less so.