A Rocky Pathway To Life's Origins

Research scientist studies common rocks for chemical clues to Earth's first organisms

December 29, 2006|By Dennis O'Brien | Dennis O'Brien,Sun Reporter

For decades, scientists have looked for clues to the origin of life in out-of-the-way places: in ancient rock formations, in the heart of meteorites, in deep-ocean hydrothermal vents and even in the soil on Mars.

But Robert Hazen thinks the secret to learning how life emerged from the primordial soup may be much closer - in the common rocks that litter his office at the Carnegie Institution in Washington.

Hazen, a research scientist at Carnegie's Geophysical Laboratory, says the important thing is how common such rocks are - and how common they were when the first tiny organisms appeared on Earth.

"The nice thing about minerals is they were everywhere. Tidal pools, volcanic slopes, undersea vents," Hazen said. "Any place you go had rocks and minerals."

Hazen and others looking for the secrets of life are motivated by the most elemental forces of curiosity: If all life evolved from a common ancestor, shouldn't we try to find it and understand it?

Besides, they say, think of the implications of finding a chemical pathway to life's origins - given the possibility of habitable planets scattered across the universe.

"It's one of the greatest questions humans have asked themselves throughout history," Hazen said. "And if we find there is a chemical pathway to life, we'll know we're not alone in the universe."

To pry the information he needs from its hiding places, Hazen has modified an instrument called a microarray. It normally analyzes samples of DNA, but he uses it to measure how well molecules of certain chemicals - the ones scientists call the building blocks of life - stick to his rocks and minerals.

It's just one of the devices that have helped scientists learn about life's origins since the chase began in 1953. That's when Harold C. Urey and Stanley L. Miller of the University of Chicago filled enclosed flasks with gases that they thought would mimic Earth's early atmosphere. When they struck the gasses with artificial lightning, the experiment produced amino acids that are precursors to life.

Later research showed that the colleagues were probably wrong about the makeup of the early atmosphere - but scientists nonetheless credit them with sparking today's intense interest in uncovering life's origins.

"People may have been thinking about it, but they were the ones who went into a laboratory and actually did the experiment," said James Ferris, a professor of chemistry and chemical biology at Rensselaer Polytechnic Institute and director of the New York Center for Studies on the Origins of Life.

Scientists probing life's origins have always faced major hurdles. Not the least is a shortage of clues going back to life's starting point - an estimated 4 billion years ago.

Here's why: To become living cells, smaller molecules first had to join and form larger, more-complex organic molecules. For that to happen, they had to have a central point - a cradle of sorts - where they could all gather.

"We're trying to see if just the right molecules will stick to the surface of the minerals" that were available at the time, said Hazen of his approach, outlined in the December issue of American Mineralogist and a recent presentation at a National Academy of Sciences conference in California.

Elsewhere, fossils discovered in Western Australia show the existence of cyanobacteria - organisms similar to those in today's oceans - some 3.5 billion years ago.

But the fossils give up few hints about how those early life forms developed. "We have no geological record, no way of looking at all of this by picking up a rock," said Jeffrey Bada, an expert on life's origins at the Scripps Institute of Oceanography.

Another issue is where to start looking: The sheer variety of life on Earth creates a daunting number of possibilities.

Some scientists believe the mix of minerals and compounds around undersea hydrothermal vents is a good starting point.

Others are intrigued by researchers from Oregon State University, who discovered an undersea ridge off the Galapagos Islands in 1977 where one-celled organisms thrive on rock surfaces at depths of more than a mile. Never exposed to sunlight, they draw energy from other microbes.

Meanwhile, the discovery of amino acids on a meteorite that hit near Melbourne, Australia, in 1969 has led to speculation that life's building blocks came from asteroids or interstellar debris falling to Earth.

Some experts look to Mars for clues about life on Earth. Mars was wet in its early history, with temperatures that could have supported primitive life-forms. It also has a surface that, unlike Earth, has been frozen in time, said the Scripps Institute's Bada.

Researchers at Carnegie and Scripps are designing instruments to probe Martian soil as part of future NASA missions. "There's all sorts of proposals out there, because we don't know what the answer is," Ferris said.

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