David Stonehouse Science & Health

A quest for the origin of life

Scientists aren't just looking for evidence of life on Mars, they're hoping for an answer to mankind's most nagging question: How did life begin on Earth?

By David Stonehouse

As NASA's intrepid rover Spirit wheels its way across the dusty Mars terrain providing captivating new glimpses of our planetary neighbour, scientists are hopeful it will turn up something much more elusive: proof of life.

The mission is churning up new excitement in an old quest for evidence that life on the barren and frozen planet is -- or was -- possible.

At its heart, though, the quest is deeper and much more far-reaching. Should life indeed be found there, scientists hope that will help explain how life began on Earth.

"The central question is understanding the origin of life," says Hojatollah Vali, a McGill University scientist who was part of a NASA research team that claimed in 1996 to have discovered evidence of life inside a Martian meteorite.

That conclusion has largely been dismissed, but the work sparked intense interest in the search for life on Mars which continues still today.

Mr. Vali remains hopeful.

"Mars is very similar to Earth," he says. "We hope to understand the very, very early stage of the evolution of life by getting some information from the Martian environment."

Science has been able to reach back into Earth's history only so far in the hunt for the beginnings of life here -- only 3.5 billion years or so, while the planet itself is thought to be about four billion years old.

For its first 500 million years, Earth was a volatile place with volcanic eruptions and strikes by comets and asteroids wiping out any evidence of early life.

"At the beginning, we had almost every day huge asteroids hitting the surface," Mr. Vali says. "If something formed, let's say a protein or whatever, it couldn't survive these kinds of activities."

So scientists have turned to Mars, which was not nearly as chaotic during the early days of our solar system, with hope that early life has been preserved on the red planet.

Testing of ALH84001, the Martian softball-sized meteorite at the centre of the controversial 1996 NASA study, found it was 4.5 billion years old -- older than any Earth rock science has uncovered.

NASA says its testing also found material suggesting bacteria -- a primitive life form -- had fossilized inside. However, other scientists from around the world have questioned those findings, and dismissed the idea that they suggest life on Mars.

But that has not dampened the effort to find it. The Spirit rover mission, as well as that of the NASA Opportunity rover due to land on Mars next Saturday, is not intended to unearth life. But scientists are hoping the rovers will find signs of water -- which would suggest life on the planet was, or is, at least possible.

"If we can clearly show there was water on Mars in the past, I think it makes a much stronger case for life," says Peter Brown, who holds the Canada Research Chair in Meteor Science at the University of Western Ontario.

Signs of water on the planet would help bolster the thinking that Mars was once a warmer, more hospitable place, and increases the likelihood that life once thrived on the planet.

Any life found on Mars could be studied with an eye to finding out where it originated. It could also give credence to one theory that life on Earth did not originate here, but arrived aboard a meteorite from Mars.

"Discovering life on Mars and analyzing it, we may find that it has a lot in common with life here on Earth and that may suggest that life arose on one planet or the other and was then transported," Mr. Brown says.

Hope for new discoveries about the existence of life on Mars has been bolstered by the presence of "extremophiles" --creatures, often microbes, that thrive in seemingly impossible conditions, such as acid baths, deep rock or extreme temperatures.

"We're finding life kilometres below the surface of the Earth. We're finding it deep in the ocean where there is no contact with energy from the sun," says Mr. Brown. "All these so-called extremophile life forms are all very suggestive of a much higher robustness, at least for simple life, than we have previously thought in the past. That makes ancient life on Mars more likely then we would have thought, say, a decade ago."

Hopes are high that this or future missions to Mars -- such as the one announced by U.S. President George W. Bush this past week -- will lead to spectacular discoveries.

Rick Chappell, a former NASA director, talks of finding fossils or even water-filled crevices under the surface of the planet filled with unfamiliar life forms.

"One could expect that the biology of those living things is an entirely different tree of evolution that we have here on Earth," says Mr. Chappell, now director of the Dyer Observatory at Vanderbilt University in Nashville. "That would be really spectacular, if we were able to find that."

But Michael E. Lipschutz, a chemistry professor at Purdue University in Indiana who has studied extra-terrestrial materials for more than 45 years, is highly skeptical.

He says Mars is too hostile to support life and nothing has yet been found on any Martian meteorites to show it is even possible. And he says the search for water now underway will prove nothing.

"That doesn't reveal anything about the likelihood or unlikelihood of life having been there. That just says water was present," Mr. Lipschutz says.

"If I had to make a bet, I'd bet there isn't life forms on Mars."