Building Blocks of Life Formed on Early Mars?
A chunk of 4.5-billion-year-old Martian rock was found in 1984 in the Allan Hills region of Antarctica. The meteorite contains organic compounds—the building blocks of life.
New analysis of the rock, dubbed Allan Hills 84001, offers the first evidence that the organics were formed on Mars by volcanic activity and were not, as has long been thought, transported to the red planet by meteorites.
Photograph courtesy NASA
Brian Handwerk
for National Geographic News
December 13, 2007
The building blocks of life as we know it may have formed on Mars during a meeting of fire and ice, a new study reports.
The Martian meteorite called Allan Hills 84001, which was found on Earth in 1984, is known to include organic compounds—a class of molecules that contain carbon and hydrogen.
New analysis of the 4.5-billion-year-old rock suggests that these compounds were formed on Mars by volcanic activity early in the frigid planet's history.
But many experts continue to believe the long-held theory that the organics from Allan Hills 84001 were brought to Mars by meteorite impacts.
The find could have implications for the search for life on the red planet and many other frozen worlds scattered throughout the universe.
"Life as we know it requires water, and it requires these building blocks, organic molecules," said study co-author Hans E.F. Amundsen of Earth and Planetary Exploration Services in Oslo, Norway.
"We're finding evidence that some of the prerequisites that we think must be there are present" on Mars.
Icy Volcanoes
Water and simple carbon gases like methane and carbon dioxide are basic materials that can react under the right conditions to form organic compounds.
On frozen Mars those essential ingredients appear to have been cooked up by volcanoes, aided by an iron-rich mineral called magnetite.
"What's apparently happened is that you had a volcanic eruption, and things cooled very rapidly because you had a very cold climate," Amundsen said.
"Cooling carbon dioxide and water very rapidly together with iron oxide minerals [such as magnetite] has produced a reaction forming simple organic compounds."
Amundsen and co-author Andrew Steele, of the Carnegie Institution's Geophysical Laboratory, suggest that a similar reaction occurred on Earth in Svalbard, Norway, about a million years ago.
Svalbard's prehistoric Arctic climate was possibly analogous to the hostile conditions found on ancient Mars.
Comparisons of organic material in rocks from Svalbard with those in the Martian meteorite suggested that the same process for forming organics was at work in both locales.
"We know that in Svalbard, when the climate was even colder than today, these eruptions [caused] hot lava [to] erupt through a very thick ice sheet," Amundsen said.
"The lava cooled rapidly, trapping minerals from the Earth's mantle, and that's when you had the reactions that formed these organic compounds."
The analysis is described in the current issue of the journal Meteoritics and Planetary Science.
The study authors also suggest that organics could be forming on scores of other cold, rocky planets across the universe.
"If you have volcanic activity on such planets, and water and carbon dioxide present, you could have the same reaction going on anywhere," Amundsen said.
"Homegrown" or Not?
But not everyone is convinced by the new analysis.
Jeffrey Bada, an expert on life origins at Scripps Institution of Oceanography at the University of California, San Diego, suggests caution.
"My take is that these meteorites are so complicated that to make bold claims on what the organic material is, where it came from, and what its implications might be is just not very credible," he said.
Much of the meteorite's carbon, Bada reports, is from contamination when it smashed into Antarctica's Allan Hills.
"You do see a tiny amount of carbon that does appear [to be different] than you'd expect from a terrestrial material," he added.
But Bada reiterated the longstanding theory that such organics were not homegrown and were likely delivered to Mars by meteorites.
"How [one] can tell that these organic compounds are not due to meteorite infall is perplexing."
Based on his studies of the meteorite's contamination, study co-author Steele remains convinced the carbon has a Martian origin.
"It is very difficult to see how the carbon came from meteorite infall," he said. "The carbon itself and the magnetite it is associated with would have to penetrate the minerals within the meteorite. That is impossible." NASA's 2009 Mars Science Laboratory mission, of which Steele is a member, could help resolve the debate.
"One of the goals is to detect organic compounds on Mars," study co-author Amundsen said.
"Now that we know they are there, and what kind of setting they are in, it's a matter of guiding that robot when it gets up there to hopefully find the same stuff."
