HOLD FOR RELEASE: THURSDAY, FEB. 13, 1997, 8:30 A.M. PST
Contact: Larry Bernard
Office: (607) 255-3651
Internet: [email protected]
Compuserve: Larry Bernard 72650,565
http://www.news.cornell.edu
SEATTLE -- Subsurface life on Mars probably did exist and may still exist
for the same reason it exists on Earth -- both these planets and many other
planetary bodies in the solar system are made of similar stuff and provide
similar conditions, a Cornell University astronomer said today (Feb. 13).
Microbes deep inside the Earth's crust get oxygen from rocks and use it to
oxidize hydrocarbons that come streaming up from below, receiving energy by
this process. It now seems probable that life evolved by such processes
from the inside out, rather than commencing at the surface, said Thomas
Gold, Cornell professor emeritus of astronomy. The same scenario is likely
to be true for Mars and several other planetary bodies, he said.
Gold, a member of the National Academy of Sciences, described this theory
at the annual meeting of the American Association for the Advancement of
Science (AAAS) on Thursday, Feb. 13, at a session on "New Worlds and Old
Worlds" in a talk called "Was There and Is There Life on Mars?"
His answer: Yes, there was and probably still is. "Microbial subsurface
life has existed on Earth for billions of years and still does," Gold said.
"It is very likely that we will find a deep, hot biosphere on Mars, as we
have found on Earth, and probably on many other planetary bodies in our
solar system."
Gold first proposed his theory in a 1992 paper, "The Deep, Hot Biosphere,"
in the Proceedings of the National Academy of Sciences (July 1992). In it
he wrote that the Earth contains internal chemical energy sources in which
microbes thrive, using hydrogen, methane and other liquids and gases that
percolate up through cracks from the planet's interior, together with
oxygen and other components of the local rocks. He suggested that such
microbial life probably would be found in many areas below the surface of
the Earth and will exist also on many other bodies, such as the moon, Mars,
many asteroids between Mars and Jupiter, Titan (satellite of Saturn) and
Triton (satellite of Neptune) and other satellites of the giant planets,
and Pluto, the farthest known planet, where similar fluids have come up
from below.
Further, he suggested in the 1992 paper that the known meteorites found on
the Earth and identified as having come here from Mars should be examined
for evidence of such microbial life. He also suggested that the search for
such evidence of life would become a central issue in planetary research.
Last year one of these meteorites was found to contain what many scientists
believe is evidence for such life. Gold considers this evidence to be
particularly strong because the meteorite, Meteorite ALH84001, contains
solids that are known on the Earth to be residues of such microbial
activity.
The key to his theory, he said, is that petroleum has come up from great
depth, not from biological sediments generated at or near the surface. The
clearest evidence for that: helium.
The chemically inert gas, helium, is found to be strongly associated with
petroleum all over the Earth, Gold said. This is true not only for great
petroleum deposits, but also in detail in gases that are measured in
thousands of locations at shallow depths. Yet no chemical process exists
in which biological sediments would have concentrated this gas.
Helium is generated diffusely by the decay of uranium and thorium in the
rocks. Gold is first to suggest that fluids, such as petroleum, that have
washed through great distances in the rocks flush out the small quantities
of helium that have accumulated along their way, increasing the helium
concentration in such fluids.
"This is the only possible mechanism. Why else would helium be found
together with petroleum?" Gold asks. "The association of helium with
biological matter has not been accounted for in any other way."
If so, this requires that petroleum has come up from great depths, like 100
miles or more, rather than from just the upper four miles or so where there
are biological sediments.
"In that case all the biological components that petroleum contains must
have been additions it obtained later at the shallower levels from which we
extract it," Gold said. What accounts for this biology? Microbial life,
he said.
It was for this reason, Gold said, that he had to suppose that there was a
huge amount of microbial life at all these shallower levels. "At the
levels to which we drill, petroleum is a wonderful food for microbes," Gold
said. "They thrive on that. With this combination we can understand why
there is helium in petroleum and at the same time why there are biological
molecules in it also."
And if it is true that hydrocarbons are cooked deep inside the Earth and
then are mechanically washed up by geologic forces, where microbes then
feed on them, then it's just a small step to wonder whether similar
processes would not exist on other similar bodies in the solar system, he
said.
"The Earth, then, has no particular prerogative to develop microbial life.
Its subsurface is not unique. We know there are petrochemicals under the
surfaces of many other bodies in the solar system, and in fact most other
solid bodies have shown evidence of hydrocarbons."
The Martian meteorite ALH84001, which is thought to contain evidence of
life, as announced in a paper in the journal Science (Aug. 16, 1996) by
David McKay of NASA and others, has other similarities to Earthly
subsurface life, Gold said.
"For example, unoxidized sulfur compounds and concentrations of small
grains of the iron mineral magnetite, both not common in rocks, are found
frequently around oil wells on Earth -- solid refuse left behind by
microbial activity," Gold said. The meteorite ALH84001 has iron sulfide
and magnetite, "very suggestive of the processes we see here," he said.
He added that the present or past surface condition on Mars is irrelevant
to this problem. A huge impact was required to eject material from Mars,
including the meteorites that have been found in Antarctica. Most of this
ejected material would have come from deep inside the planet, from the
crater this impact would have generated. A small distance down into such a
crater, a mile or two, one would find liquid water and hydrocarbons, Gold
said.
His 1992 suggestion on how to find evidence of life by spacecraft missions
to Mars still holds, he said. There are areas on Mars where huge
landslides have exposed material that once was at a depth of two miles or
more, certainly into the depth range of liquid water. Why not select such
locations for a robotic vehicle landing with a sample return capability?
Gold asked. Now as a result of the meteorite investigation, NASA is
planning to send probes on Mars missions to look for further evidence of
life.
Said Gold: "As long as you think that life is possible only on planetary
surfaces, the Earth is uniquely suitable. But when you talk about life
deep below, the Earth is not unique at all. The deep, chemically supplied
life may be common, not only in the solid bodies of the solar system, but
throughout the universe."
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EDITORS: Tom Gold will participate in a AAAS news conference at 1 p.m. PST
on Friday, Feb. 14, Room 201 Seattle Convention Center. Gold can be
reached at the AAAS meeting Feb. 12-14 at the Seattle Hilton, (206)
624-0500. After Feb. 15, he can be reached at (607) 257-6696. Larry
Bernard of the Cornell News Service can be reached in the AAAS newsroom or
at the Sheraton Seattle, (206) 621-9000, Feb. 13-18, or at (607) 255-3651
after Feb. 18.
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