by Richard Peachey
In August 1996, a group of scientists published their claim that life may have existed on Mars at one time (David S. McKay et al. 1996 [Aug. 16]. "Search for Past Life on Mars: Possible Relic Biogenic Activity in Martian Meteorite ALH84001." Science 273:924-930).
Their claim was based on study of a potato-sized rock found in Antarctica (on Earth!), designated ALH84001 (discovered in the Allan Hills area in 1984).
This rock is alleged:
(1) to have been formed 4.5 billion years ago on Mars;
(2) to have been blasted into space by a meteorite impact about 1.5 million years ago;
(3) to have landed on Earth 13,000 years ago;
(4) to contain evidence that life existed on Mars.
WHAT'S THE EVIDENCE?
The proposed evidence of Martian life in the rock consists of:
(1) tube-like carbonate globules that superficially resemble the shape of bacteria;
(2) the presence of molecules called “polycyclic aromatic hydrocarbons” (PAHs), which are sometimes produced (on Earth) by the decay of microbes;
(3) the presence of the minerals magnetite and iron sulfide, which are produced (on Earth) by the metabolic activities of certain bacteria.
Each of the rock features claimed as evidence for life could have arisen with or without the presence of living organisms. (The authors admit this in their 1996 article!) Many, perhaps most, scientists remain skeptical of the claim that the rock provides evidence of past life on Mars.
Some of the problems:
(1) No trace of cell walls or any remnant of cell parts were found in the rock.
(2) The carbonate globules are much smaller than the smallest known Earth bacteria.
(3) Analysis of the sulfur and carbon isotope ratios in the rock has produced no evidence of biological activity.
(4) PAHs are common both among interplanetary dust particles and on Earth (e.g., in coal tar). So the PAHs in the rock could have come from elsewhere to Mars, or from terrestrial contaminants, not necessarily from Mars itself. In any case, PAHs are not proof of life.
(5) It is questionable whether a meteorite impact on Mars could have blasted a rock out of the pull of Mars’ gravity.
(6) The magnetite crystals in the rock appear unlike those known to be produced by Earth bacteria.
(7) It’s interesting that in August 1996, NASA desperately needed new funding — and the Mars rock announcement brought them new funding immediately!
NOTABLE QUOTES ON THE "MARS ROCK"
"HOUSTON—Just over 2 years ago [i.e., in 1996], NASA Administrator Dan Goldin rushed to the White House to brief the president and vice president on a discovery that was about to rock the world: signs of ancient life on Mars. 'We are not talking about "little green men," ' said Goldin, but even so, little gray worms from a meteorite that was once a chunk of Mars made the front page day after day. The microscopic features helped jump-start planetary exploration as well as the field of exobiology and left everyone from priests to pundits wrestling with the implications of learning that life on Earth is not unique.
"Since then, ALH84001, a martian meteorite scooped from the Antarctic ice cap, has become the most intensively studied 2 kilograms of rock in history. With $2.3 million in funds from NASA and the National Science Foundation, scientists have sectioned it, imaged it, identified its minerals, measured its isotopes, and analyzed its organic matter. All this effort was aimed at testing and, if possible, extending each of the original four lines of evidence for life: mineral shapes that look like fossilized bacteria, traces of organic matter, rosettes of minerals perhaps formed through bacterial action, and grains of a magnetic mineral resembling those produced by bacteria. But at a NASA workshop here [i.e., in Houston, Texas] early this month [November 1998], scientists concluded that all the effort has not strengthened the claims. Indeed, key parts of the original case have been scaled back. Most researchers agree that the case for life is shakier than ever." (Richard A. Kerr. 1998 [Nov. 20]. "Requiem for Life on Mars? Support for Microbes Fades." Science 282:1398.)
"Like most of us, William Schopf was flabbergasted when he heard in August 1996 that NASA scientists claimed to have found evidence for ancient life on Mars in an obscure meteorite.
"But it was not merely the magnitude of the claim that amazed Schopf, a palaeobiologist at the University of California at Los Angeles. When he was let in on the secret several weeks before the news broke, it was a case of déjà vu. More than a year earlier, a NASA team led by David McKay of the Johnson Space Center in Houston had flown Schopf over to look at some strange orange and black blobs in a chunk of rock chipped from the surface of Mars.
"'They thought that these might be shells of Martian protozoa,' Schopf recalls. 'But the size range was wrong, and some discs merged together. You never find that on true fossils.' Eventually, he convinced McKay that the blobs were not ancient microorganisms.
"So, when he received a draft paper from McKay's team, due to be published in Science, Schopf was surprised to see that the blobs had turned up again. 'But instead of being fossil protozoan shells, they were bacterially precipitated minerals,' he says. 'It always sort of troubled me. They really had decided, one way or the other, that there was life.'
"Schopf remains troubled, and he is not alone. Scientists now working on meteorites, prospective missions to Mars and the possibility of extraterrestrial life are funded at levels that two years ago would have been unimaginable. Had NASA's publicity machine not turned McKay's paper into a global media event, this largesse would never have been granted. Some researchers see it as a victory of hype over science. They see a tale of a government agency that took inconclusive evidence and used the media to help it win public funds. And some feel uncomfortable about the Faustian bargain they have made by accepting their share of the proceeds. . . .
"Since then, a succession of analyses has undermined the case for life in ALH84001. The scientific consensus now is that the meteorite provides no convincing evidence for life on Mars. But the possibility of extraterrestrial life still lingers in the public consciousness, and cash has flowed into NASA's astrobiology programme—its annual budget is set to grow from $9 million this year to between $15 and $20 million next year, and possibly as high as $100 million after that. According to Wes Huntress, NASA's associate administrator for space science: 'I've never done the accounting, but if you integrate over ten years, it increased funding probably by 50 per cent.' [Case Western Reserve University geologist Ralph] Harvey says: 'Whether or not it turns out to be bunk, it's done its job.'" (Charles Seife. 1998 [Aug. 8]. "Money for old rock." New Scientist 159:20f.)