Subsurface life on Mars.
I share an article on Thomas Gold opinion
13/2/1997
Life on Mars
existed for billions of years -- and may continue still -- Cornell astronomer
says
By Larry Bernard
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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