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Astrobiology: A down-to-earth view

This artist's conception shows an ice-penetrating cryobot and a submersible hydrobot that could be used to explore a hidden body of Antarctic water known as Lake Vostok as well as what appears to be an ice-covered ocean on Europa, a moon of Jupiter.
This artist's conception shows an ice-penetrating cryobot and a submersible hydrobot that could be used to explore a hidden body of Antarctic water known as Lake Vostok as well as what appears to be an ice-covered ocean on Europa, a moon of Jupiter.

The word “astrobiology” may summon up images of boldly going in search of Vulcans or even more exotic aliens. You might think it has to do primarily with Mars, or Europa, or planets around other suns. But the fact is, Topic A in the rapidly growing field of astrobiology is good old Planet Earth.

The emphasis on Earth comes through loud and clear in the agenda for NASA’s Astrobiology Science Conference, scheduled April 3-5 at Ames Research Center in California. More than half of the 51 presentations on the schedule focus on life on Earth — how it arose in the distant past, how it endures in extreme environments, how it can be affected by climate and chemistry.

“We define astrobiology in the broadest way as the study of life in the universe,” said David Morrison, who heads Ames’ astrobiology and space research directorate. And since Earth is the only place in the universe where we know life exists, “we have to start with what we know,” he said.

“One of the fascinating aspects of astrobiology is that it’s asking the same questions that mankind has been asking for thousands of years,” said Lynn Rothschild, a NASA evolutionary biologist who chairs the conference’s local organizing committee. “We tend to be a very self-centered species.”

In the classroom
Earthly matters also figure prominently at the University of Washington’s astrobiology program in Seattle, where graduate students in such fields as oceanography, atmospheric science, astronomy, geology, chemistry and mathematics pore through scientific papers and classroom seminars about life’s place in the universe. It’s considered the nation’s first doctoral program in astrobiology, supported by a five-year, $2 million grant from the National Science Foundation’s Integrative Graduate Education and Research Traineeship Program. Eight students were selected for this first year of the program.

The topic for a recent class was the Snowball Earth theory, which proposes that our planet went through a global deep-freeze hundreds of millions of years ago. In some ways, the “ice-covered Earth was similar to an ice-free Mars,” suggested University of Chicago geophysicist Raymond Pierrehumbert, the guest speaker for the day.

The discussion ranged from the roles that clouds, volcanoes and carbon dioxide levels play in determining a planet’s climate ... to different models for photosynthesis ... to plate tectonics ... to the latest findings from Mars Global Surveyor ... to the potential traces of ancient life left behind in fossil formations known as stromatolites.

That kind of scientific cross-pollination may sound dizzying, but it’s just what the students were looking for.

“I like the way different disciplines interrelate with each other,” said Craig Brown, a first-year graduate student in atmospheric sciences.

The instructors like it, too.

“Four years ago, you couldn’t get an oceanographer to listen to you for five minutes about planets,” recalled Conway Leovy, an atmospheric sciences professor who is a co-investigator in the astrobiology program. Since then, scientists have become increasingly interested in the potential parallels between the hydrothermal vents at the bottom of Earth’s oceans and the conditions that may exist beneath the surface ice on Europa, one of Jupiter’s moons.

To be or not to be?
Biologists have been surprised to find life enduring at the volcanic vents, within polar ice and in rock miles beneath Earth’s crust. At the same time, revelations about water beyond Earth and planets beyond our solar system have led astronomers to wonder whether life might have gained similar footholds in otherworldly environments.

Scientists say the quest is worth taking on, even if it turns out that life is unique to Earth. If astrobiologists find no signs of life in extraterrestrial environments that are similar to Earth’s, “it’s equally important for us to know ... why not?” Rothschild said.

Whether or not there’s life out there, it’s essential to take a closer look at life down here, Morrison said. He voiced particular interest in Earth’s extreme environments and the largely undiscovered world of microscopic organisms.

“If you dug up a bucket of dirt in your back yard, you’d find more microbes in there than there are stars in the galaxy, and 99 percent of them are unknown,” he said.

That’s why some of the presentations at the astrobiology conference focus on microscopic organisms found within Arctic sea ice, or within the hot springs of Yellowstone National Park, or within boiling-hot sulfide chimneys on the bottom of the Pacific. Such organisms seem to be the most likely suspects in the search for life beyond Earth.

In fact, two University of Washington researchers argue that microbes might well be the only kind of life that scientists could ever expect to find out there. In the book “Rare Earth,” paleontologist Peter Ward and astronomer Donald Brownlee say Earth benefited from a hard-to-match combination of fortunate factors — ranging from its position in the solar system and the Milky Way galaxy to global climate changes and the timing of asteroid and comet impacts.

“This may be as good as it gets in terms of diversity,” Ward said.

Ward and a colleague, astronomer Guillermo Gonzalez, are now looking into whether supernovae or other cosmic factors may have played a role in winnowing down Earth’s species.

“We still have a bunch of mass extinctions that have no (apparent) cause, but certainly we know that something caused them,” Ward said.

Some evolutionary theorists argue that the development of complex life was driven by close shaves that required organisms to adapt or die — a cosmic manifestation of the saying, “That which does not kill us makes us stronger.” If that’s the case, then the path toward higher species traced a narrow line between the torpor of unconsciousness and the terror of extinction.

Even researchers involved in the search for radio signals from extraterrestrial civilizations acknowledge that intelligent life must be far rarer than mute microbes. Otherwise, the galaxy would be busier than the alien-filled cantina in the movie “Star Wars.” But they contend that even if complex life is exceedingly rare, the vast number of stellar systems in our galaxy evens out the odds.

Ward admits he’s had some healthy debates with SETI researchers and calls them “first-class” scientists — who happen to hold a different point of view.

“We really have to agree to disagree on some of these unknowable questions,” he said.