- Life forms so alien that scientists may
simply not have recognised evidence of their existence could inhabit the
Earth, according to a leading scientist.
- Dr. Tom Gold, emeritus professor of astronomy
at Cornell University in America, believes that organisms based on silicon
- completely unrelated to all the carbon-based life man has encountered
so far - may live at great depths.
- In a forthcoming book he will suggest
that scientists should take the possibility more seriously. Gold, who is
a member of the Royal Society, previously predicted that vast amounts of
more conventional bacteria live miles down within the Earth's crust. Scientists
initially dismissed the idea, but many now agree with him.
- "So long as nobody suspects there
could be silicon-based life, we may just not be clever enough to identify
it," he said last week.
- Rocks bearing signs of silicon-based
organisms may already be sitting in laboratories, he believes, with their
- Every known living organism, from bacteria
to mankind, is based on the chemistry of carbon, which forms the complex
molecules such as DNA that are central to our existence. Scientists believe
that if extraterrestrial life is found, the chances are that it, too, will
- Silicon has many chemical similarities
to carbon, prompting scholars and science fiction writers to dream up new
life forms. Huge "space slugs" that can swallow space ships appear
in the film The Empire Strikes Back; in an episode of Star Trek a rock-like
alien attacked Captain Kirk's crew; and killer parasites based on silicon
surfaced in The X-Files when scientists explored the interior of a volcano.
- Gold's life forms, if they exist, would
most likely be micro-organisms capable of withstanding enormous pressures
and temperatures, living in tiny pores inside rock deep within the Earth's
crust. They could draw energy from dissolved gases and surrounding minerals.
- Gold's ideas, which centre on an alternative
explanation for oil and mineral deposits, will be published in his book,
The Deep Hot Biosphere, in January.
- "It is speculative but logical that
there could be a large bio-chemical system very deep down which works better
at high temperatures and pressures," he said.
- Others are sceptical. Dr Harold Klein,
who headed the Viking lander project team that searched for signs of life
on Mars in the 1970s, pointed out that silicon was far inferior to carbon
at forming the complex polymers crucial for life.
- "I personally doubt the idea of
silicon-based life. If we do find organisms far down inside the Earth,
I'd bet they'd be carbon-based," he said.
- Nevertheless, he urges future missions
to Mars to carry an instrument to test for non-carbon-based organisms -
just in case. It is possible that the chemistry of silicon is altered sufficiently
by the great temperatures and pressures deep in the Earth to make it more
suited to forming complex molecules, according to David Noever, a research
scientist at Nasa's new Astrobiology Institute.
- He said some scientists at the American
space agency were treating the idea of silicon-based organisms seriously,
particularly with a view to searching for extraterrestrial life.
- "It's almost naive to assume all
life must be carbon-based; I could possibly make good cases for life based
on both silicon and phosphorus," he said.
- Silicon is used by some carbon-based
single-cell organisms called diatoms to form protective shells, according
to Dr David Williams, a diatom researcher at the Natural History Museum
in London. But diatoms are still fundamentally carbon-based.
- However, bizarre organisms have been
found in recent years deep in the Earth's crust. Steve Jones, professor
of genetics at University College London, said: "There's an unknown
universe down there that has already produced organisms with metabolisms
so strange that, by comparison, man and mushrooms are almost identical,
so God knows what else they'll find."
- Microbes have been found living on the
ocean floor at depths and temperatures where life was previously thought
- Without knowing what silicon-based life
forms might be like, said Dr Harry Elderfield, an earth scientist at Cambridge
University, it is almost impossible to predict how scientists could even
test for them.
- Yet Gold has been described by Stephen
Jay Gould, president of the American Association for the Advancement of
Science, as one of the most iconoclastic scientists - but one who is often