Mars meteorite ALH84001 holds shapes and chemical evidence that the researchers say points to bacterial life. (AFP Photo/Nasa)

By Kathy Sawyer
Washington Post Staff Writer
Friday, March 19, 1999; Page A3

Two and a half years ago, researchers from NASA and Stanford University shook the world with the announcement of possible signs of ancient microbial life in a rock from Mars. It was a drama worthy of "The X-Files," complete with high-level secrecy, leaks, a mobbed NASA news conference and global ruminations about what it all meant.

Since the 1996 announcement, fragments of the rock have been sliced, probed and measured by dozens of scientists in many fields, spurred by more than $2 million in new government funding, in an intense effort to test the extraordinary claim.

Today, most scientists who have studied the samples, or studied the studies, have concluded that the various lines of evidence in the rock are either disproved, shaken or inconclusive.

Even the researchers who made the original claim acknowledge that they have failed to convince many of their colleagues. "At this point, we are clearly in a minority in still believing this evidence indicates life in the meteorite," David McKay of NASA's Johnson Space Center in Houston, leader of the original discovery team, said this week.

Bloodied by critics but unbowed, his team maintains that there are enough unexplained signs in the rock to keep their hypothesis alive, and they intend to keep hunting for an unmistakable biological signature from Mars – such as cellular structure – that will satisfy the critics. Yesterday, at a science meeting in Houston, McKay and Kathie Thomas-Keprta, another member of the original team, presented preliminary evidence of possible fossilized bacteria in a second Martian meteorite as well as additional work on the first rock. And they are braced for another wave of criticism from fellow researchers.

The issues raised by the first rock, which some thought would be resolved quickly, have been unexpectedly complicated. The wrangling over the evidence, at numerous meetings and soirees and in published papers, brings to mind the image of prickly angels dancing, elbows out, on the head of a pin. The flooring in this case is deep inside that fist-sized rock, within golden globules that are much smaller than pinheads, where the researchers have found remarkably rich troves of mystery and nuance, layers of complexity and conflicting meaning. The scientific process in this case has often been laced with bitter personal rivalries, revved up by the high stakes and public attention.

One thing everyone seems to agree on is that, at the very least, the esoteric Mars rock debate has called valuable attention to humanity's stunning ignorance when it comes to identifying life, on Earth or elsewhere. "My personal opinion is that it's probably over for this particular rock," said John Bradley of Georgia Tech, a geochemist and executive director of MVA Inc. of Norcross, Ga. "But one of the neat things we've learned from it is how little we know about life on Earth."

The provocative clues in the original Mars rock, known as ALH84001, along with recent findings about the prevalence of planets and the ease with which life may arise under extreme conditions, have inspired new avenues of inquiry and the development of new techniques aimed at deciphering the semaphores of life wherever they may be found.

Chemist Richard Zare of Stanford, a member of the original team, said this week that despite a "rush to judgment" among researchers, "the hypothesis remains neither proved nor disproved. Its major impact has been to elevate the scientific discourse on this topic and to provide a very compelling reason why we want to explore the planets."

The research has been funded by NASA and the National Science Foundation. Although some critics have charged NASA with hyping the story to pump up funding, NASA officials said the agency takes no official position on the validity of the theory. "Our mission has been to fund the research so the science community could find the truth," said Michael Meyer, NASA's chief astrobiologist. "Science is not a 'majority rules' kind of a thing" but turns on the strength of the arguments.

The evidence that created all the stir was contained in and around the golden pancakes of carbonate minerals along the rock's interior cracks, possibly deposited by fizzy Martian groundwater billions of years before the rock was blasted off the planet's surface some 16 million years ago in an asteroid impact.

The original evidence presented in August 1996 included: wormlike shapes that resemble fossil bacteria swimming in formation; incompatible minerals commingled in a way that is sometimes associated with organic activity; carbon compounds that sometimes suggest decayed organic matter; and small crystals of an iron oxide known as magnetite that, on Earth, is a byproduct of bacteria.

The McKay team declared in the initial announcement that no single one of these observations alone was conclusive evidence of past life, but the confluence of all of them together constituted "evidence of primitive life on early Mars."

To the extent that McKay's original hypothesis depended on all four lines of evidence working together, "the hypothesis has not succeeded," writes meteorite specialist Allan Treiman, of the Lunar and Planetary Institute in Houston, in the April issue of Sky & Telescope. But in a broader sense, he concludes, "the jury is still out."

Many microbiologists rejected the attention-getting "worms" from the start as too small: much smaller than the smallest known bacteria on Earth, and too small to contain the minimum machinery of life (as we know it). Since then, researchers have discovered an unexpectedly tiny form of bacteria on Earth. However, McKay said, he has given ground by accepting arguments from Bradley and others that the tiniest of the worms are actually ridges formed by minerals unaided by living organisms and could have been altered by routine lab procedures.

McKay now argues that the larger lifelike shapes may be body fragments, rather than whole microbes. But if they represent creatures at all, critics counter, they could be earthlings, in light of recent findings by other NASA researchers that microbes sometimes colonize meteorites in Antarctic ice and can fossilize rapidly after they die.

The golden globules are also packed with PAHs (polycyclic aromatic hydrocarbons), a common type of organic molecule that may or may not be associated with dead organisms. Some of the most intense arguments have been about whether the PAHs originated on Mars or represent contamination from Antarctic ice. No one disputes that the rock is heavily contaminated with organic matter picked up on Earth, but Simon Clemett, one of the original McKay researchers, has found that no other Antarctic rocks are similarly contaminated with the greasy PAHs.

Much of the debate has centered around whether the carbonate pancakes formed at temperatures either too hot or too cold for life. Research groups have variously concluded that they formed in icy cold, or in conditions hotter than molten lead, but Treiman and others say the majority now favor a middle range possibly but not necessarily suitable for life.

"Most of these disagreements are not about facts, but their interpretation," said Treiman, "In its way, ALH84001 is a Rorschach test for researchers – we see what we are trained to see."

The strongest evidence remaining, by most accounts, is in magnetite crystals rimming the globules. Until recently, they were known to be produced only by unusual bacteria for the purpose of sensing Earth's magnetic field and orienting themselves as to "up" and "down" for more efficient foraging. Since 1996, scientists have learned a lot more about magnetites and their diversity. While some of the magnetite grains in the rock now can be explained by inorganic processes, Thomas-Keprta has found that about 25 percent of those in ALH84001 are of a type that, so far, has been found to be made only by living organisms.

Yesterday at the meeting at the Lunar and Planetary Institute, she and McKay, along with Joseph Kirschvink, a paleomagnetism specialist at the California Institute of Technology, presented further analysis to support the magnetite case. McKay and Thomas-Keprta also discussed features they have discovered in the Nakhla meteorite that exploded over Egypt in June 1911. The tiny fossil-like structures are larger than those in the first meteorite and close to the size range of known Earth bacteria. Some have whiplike protuberances that resemble those in bacteria. And they are dispersed like bacterial colonies would be, rather than spread uniformly like chemical precipitates. Yet to be resolved, McKay acknowledged, is whether they are indeed fossil life forms and, if so, whether they are native to Mars or Earth.