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By Sean Henahan, Access Excellence

Seattle, WA (2/17/97) Is, or was, there life on Mars? This basic question stirred lively debate at the annual meeting of the American Academy for the Advancement of Science.

Graphic: False-color backscatter electron (BSE) image of fractured surface of a chip from ALH84001 meteorite showing distribution of the carbonate globules.

At the center of the controversy is a Martian meteorite, known as Alan Hills 84001, which was found in Antarctica about 13 years ago. It formed on Mars 4.5 billion years ago and appears to have come in contact with liquid water between 3.6 billion and 4 billion years ago. From the water sprouted mineral deposits that bear a strong resemblance to fossilized bacteria.

Researchers believe that about 16 million years ago, a comet or asteroid struck the Martian surface and blasted pieces of the rock into space, where they drifted for millions of years. The meteorite, found in Antarctica in 1984, fell to Earth about 13,000 years ago.

However, some naysayers were quick to question the claims of Martian life, offering various potential alternative explanations to the findings, from contamination of the sample to natural, but non-biological possibilities.

Cornell researchers believe that not only was there life on Mars long ago, there is a good possibility that lifeforms may still exist today on the red planet. The researchers argue that there may be life below the surface of Mars for the same reason it exists on Earth, noting that both planets are made of similar stuff and provide similar conditions.

Microbes deep inside the Earth's crust get oxygen from rocks and use it to oxidize hydrocarbons that come streaming up from below, receiving energy by this process. It now seems probable that life evolved by such processes from the inside out, rather than commencing at the surface, said Thomas Gold, Cornell professor emeritus of astronomy. The same scenario is likely to be true for Mars and several other planetary bodies, said Gold, a member of the National Academy of Sciences

"Microbial subsurface life has existed on Earth for billions of years and still does," Gold said. "It is very likely that we will find a deep, hot biosphere on Mars, as we have found on Earth, and probably on many other planetary bodies in our solar system."

He noted that the Earth contains internal chemical energy sources in which microbes thrive, using hydrogen, methane and other liquids and gases that percolate up through cracks from the planet's interior, together with oxygen and other components of the local rocks. He suggested that such microbial life probably would be found in many areas below the surface of the Earth and will exist also on many other bodies, such as the moon, Mars, many asteroids between Mars and Jupiter, Titan (satellite of Saturn) and Triton (satellite of Neptune) and other satellites of the giant planets, and Pluto, the farthest known planet, where similar fluids have come up from below.

He suggested that the known meteorites found on the Earth and identified as having come here from Mars should be examined for evidence of such microbial life. He also suggested that the search for such evidence of life would become a central issue in planetary research.

Dr. Gold considers the evidence for Martian life to be particularly strong because the meteorite ALH84001 contains solids that are known on the Earth to be residues of such microbial activity. The key to his theory is that petroleum has come up from great depth, not from biological sediments generated at or near the surface. The clearest evidence for that: helium.

The chemically inert gas, helium, is found to be strongly associated with petroleum all over the Earth, Gold said. This is true not only for great petroleum deposits, but also in detail in gases that are measured in thousands of locations at shallow depths. Yet no chemical process exists in which biological sediments would have concentrated this gas.

Helium is generated diffusely by the decay of uranium and thorium in the rocks. Gold is first to suggest that fluids, such as petroleum, that have washed through great distances in the rocks flush out the small quantities of helium that have accumulated along their way, increasing the helium concentration in such fluids.

"This is the only possible mechanism. Why else would helium be found together with petroleum?" Gold asks. "The association of helium with biological matter has not been accounted for in any other way."

If so, this requires that petroleum has come up from great depths, like 100 miles or more, rather than from just the upper four miles or so where there are biological sediments.

"In that case all the biological components that petroleum contains must have been additions it obtained later at the shallower levels from which we extract it," Gold said. What accounts for this biology? Microbial life, he said.

It was for this reason, Gold said, that he had to suppose that there was a huge amount of microbial life at all these shallower levels. "At the levels to which we drill, petroleum is a wonderful food for microbes," Gold said. "They thrive on that. With this combination we can understand why there is helium in petroleum and at the same time why there are biological molecules in it also."

And if it is true that hydrocarbons are cooked deep inside the Earth and then are mechanically washed up by geologic forces, where microbes then feed on them, then it's just a small step to wonder whether similar processes would not exist on other similar bodies in the solar system, he said.

"The Earth, then, has no particular prerogative to develop microbial life. Its subsurface is not unique. We know there are petrochemicals under the surfaces of many other bodies in the solar system, and in fact most other solid bodies have shown evidence of hydrocarbons."

USGS Scientist Michael Carr, an astrogeologist with the U.S.Geological Survey in Menlo Park, Calif. offered further support for the idea of life on Mars.

"There is mounting evidence that Mars is a water-rich planet that may have experienced warmer climates, and therefore, life, in the past. Furthermore early terrestrial life may have evolved in hydrothermal environments resembling those in Yellowstone Park and along mid-ocean ridges and such environments were likely common on early Mars."

Carr said that both Earth and Mars experienced an early era of heavy meteorite bombardment that ended 3.8 billion years ago. Evidence for life is found in 3.8 billion year old terrestrial rocks, indicating that the Earth recovered remarkably quickly from this era of large and presumably sterilizing impacts. "We do not know what happened on Mars, but conditions on the two planets at that time could have been quite similar."

Upcoming unmanned missions to Mars will certainly provide important new data, he stressed. The Mars Global Surveyor will map various properties of the surface from orbit, and Mars Pathfinder will land a small rover at the mouth of a large flood channel. Other missions will follow in the 1998 and 2001.

Carr said a major goal of those missions is to return samples to Earth later in the decade from "places that we judge will have the best chance of revealing whether there was life on Mars in the past."

Some scientists were far too quick to condemn the martian meteorite findings, according to Dr. Christopher Romanek, of the University of Georgia's Savannah River Ecology Laboratory in Aiken, S.C.

"It's time to pry the lid off the coffin, as our interpretations are still very much alive and doing well," said. "We had nine people working on the project for three years, and just since our press conference, researchers have had to formulate and design tests, perform experiments and interpret and publish the results in an amazingly short time frame.

"While these works are admirable on these grounds alone, they do not provide the information required to resolve the current contamination and formation temperature issues we face. And yet some of the press cling to reports that ring the `death knell' for potential Martian life. Nothing could be further from the truth."

Two years earlier before the idea of Martian life ever crossed his mind, Romanek (and others) determined the Martian origin for mineral deposits or carbonate "globules" in the meteorite and determined the globules formed at a temperature capable of sustaining life. This information is crucial because extremely high formation temperatures rule out the possibility of life.

"In my opinion, it is clear the globules formed at low temperatures -- perhaps not as low as 0 to 80 degrees centigrade (as originally estimated), but surely not at the plus-or-minus 650 degrees centigrade, as suggested in one theory," said Romanek.

Romanek said that other papers, which focus on individual aspects of the NASA team's Science paper, fail to take into account all features in the carbonate globules collectively.

Romanek does not discount the possibility that future studies could provide a convincing alternative explanation for the formations found inside the meterorite, but for now, he believes the original conclusions of the study still offer the best explanations.

"We are completely open to new ideas and tests that will resolve the issues at hand, but these ideas need to be fully explored before informing the public," said Romanek. "I think we can resolve the issues of formation temperature and contamination soon, and we should do so with all expediency. If it turns out that either issue precludes a biologic origin for the features we found, we can move on to the many other exciting opportunities that our research has provided concerning processes on the surface of Mars."

Related information on the Internet

AE: Interview with Stanly Miller

AE: Life on Martian Meteorite?

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