Follow the Nitrogen to Extraterrestrial Life

http://www.usc.edu/uscnews/stories/12380.html

Follow the Nitrogen to Extraterrestrial Life

The narrow search for water can miss important clues, say USC
geobiologists.

By Carl Marziali
University of Southern California
May 4, 2006

The great search for extraterrestrial life has focused on water at the
expense of a crucial element, say USC geobiologists.

Writing in the Perspectives section of the May 5 issue of Science, four
USC researchers propose searching for organic nitrogen as a direct
indicator of the presence of life. Nitrogen is essential to the
chemistry of living organisms.

Even if NASA were to find water on Mars, its presence only would
indicate the possibility of life, said Kenneth Nealson, Wrigley
Professor of earth sciences in USC College.

"It's hard to imagine life without water, but it's easy to imagine
water
without life," Nealson said.

The discovery of nitrogen on the Red Planet would be a different story.

"If you found nitrogen in abundance on Mars, you would get extremely
excited because it shouldn't be there," Nealson said.

The reason has to do with the difference between nitrogen and carbon,
the other indispensable organic element.

Unlike carbon, nitrogen is not a major component of rocks and minerals.
This means that any substantial organic nitrogen deposits found in the
soil of Mars, or of another planet, likely would have resulted from
biological activity.

Dimming the hopes of life-on-Mars believers is the makeup of the
planet's atmosphere. The abundant nitrogen in Earth's atmosphere is
constantly replenished through biological activity. Without the ongoing
contribution of living systems, the atmosphere slowly would lose its
nitrogen.

The extremely low nitrogen content in the Martian atmosphere suggests
that biological nitrogen production is close to zero.

However, the authors write, it is possible that life existed on Mars at
some hypothetical time when nitrogen filled the atmosphere.

Co-author Douglas Capone, Wrigley Professor of environmental biology in
USC College, said NASA should establish a nitrogen detection program
alongside its water-seeking effort. He noted that next-generation
spacecraft will have advanced sampling capabilities.

"What we're suggesting here is basically drilling down into geological
strata, which they're going to be doing for water anyway," Capone said.

"The real smoking gun would be organic nitrogen."

Said Nealson: "If your goal is to search for life, it would be wise to
include nitrogen."

In their acknowledgments, the authors thanked the students of the
Spring
2004 Geobiology & Astrobiology course at USC, with whom Nealson and
Capone began their discussion on how to search for life outside earth.

"That's really what stimulated this [paper]," Nealson said.

The authors also thanked NASA, the U.S. Department of Energy and the
National Science Foundation for their financial support.

Along with Nealson and Capone, USC graduate student Beverly Flood and
former USC research professor Radu Popa (now a professor of biology at
Portland State University) contributed to the Perspectives paper.