The chance of detecting life outside our own solar system probably is
greater than discovering it on neighboring planets and moons like
Mars or Europa, a moon of Jupiter, according to a University of
Colorado at Boulder professor.
Molecular, cellular and developmental biology Professor Norman Pace,
a world-renowned biochemist and expert on life in extreme
environments, said the chances of finding primitive life in thermal
vents on Mars are not that promising. Perhaps the next likeliest
place in the solar system to find life — in the ice on Europa — is
significantly more of a long shot, he said.
“The basic theme here is that if you look at what is required for
life, it really is a narrow window,” said Pace. “Our solar system
outside Earth doesn’t seem too promising to sustain life, but we
don’t know what kind of extreme conditions conducive to life may be
found elsewhere in the universe.”
Pace gave a talk, “Molecular Perspectives of Extreme Life,” at the
2002 American Association for the Advancement of Science meeting in
Boston held Feb. 14 to Feb. 19.
Signs of life elsewhere in the galaxy or universe may be
“co-occurring, non-equilibrium gases like oxygen and methane, an
indication the gases are being replenished,” said Pace. This mngi
readily could be explained by the influence of life.
And should intelligent life out there be looking back, Earth could
possibly be seen as a home for life by other life forms in distant
galaxies working with very advanced telescopes and spectrometers like
scientists on Earth are developing to locate such gaseous conditions,
he said. Pace also is a member of CU-Boulder’s Center for
Astrobiology.
In contrast, the search for life on Mars and Europa requires a
rigorous chemical analysis, a process Pace has observed first-hand
both in deep geothermal vents in the sea and in geothermal vents in
Yellowstone National Park. That process involves the oxidation and
reduction of geothermal compounds using hydrogen and carbon dioxide
to form methane, or using hydrogen sulfide and oxygen to produce
sulfuric acid.
“We commonly see these processes with sediments under seawater,” he
said. The top 1 centimeter of some marine sediments may contain one
billion microbes per cubic centimeter. However, 1,000 meters down
into the sediments scientists only find about 100,000 microbes per
square centimeter, “and those generally are starved.”
“But if life is really going to succeed and flourish for an extended
period, I think it has to take over and modify a planet on the
surface, like it has on Earth,” Pace said. Primitive life forms in
the depths of planets or moons are not likely to contribute to
changing the surface.
The key to abundant and diverse life on the surface of Earth and
likely other planets is photosynthesis, which captures light energy
and converts it into energetic electrons that act like tiny batteries
to accomplish biochemical tasks required for life. “Life has changed
the surface of Earth dramatically,” he said.
In a piece for the Proceedings of the National Academy of Sciences
last year, Pace wrote: “Considering the intrinsic fragility and
complex organic systems coupled with the powerful force of natural
selection, I venture that the physical limits of life are likely to
be about the same anywhere in the universe.”
The definition of life should include self-replication — the
mechanism of evolution through natural selection — and probably
carbon-based molecules since carbon is one of the most abundant of
the higher elements in the universe, he said.
Given that primitive life on Earth has been found in boiling thermal
vents in the oceans to microbes in ice, the temperature span for life
anywhere in the universe is likely to range from roughly -58 degrees
Fahrenheit to 302 F, Pace said.
“We don’t know enough about Mars yet,” he said. “Perhaps the soils
under Olympus Mons — a mountain nearly 90,000 feet high — have some
type of circulation method for underground water, which would enhance
the chances of life.”
Last October, Pace was named winner of a prestigious $500,000
MacArthur Fellowship — often called a “genius grant” — from the
John D. and Catherine T. MacArthur Foundation of Chicago “for
revolutionizing our conception of the range and diversity of
microbial life.”
